The GNU Fortran Compiler

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Introduction

This manual documents the use of gfortran, the GNU Fortran compiler. You can find in this manual how to invoke gfortran, as well as its features and incompatibilities.

Table of Contents

Short Table of Contents


1 Introduction

The GNU Fortran compiler front end was designed initially as a free replacement for, or alternative to, the Unix f95 command; gfortran is the command you will use to invoke the compiler.


1.1 About GNU Fortran

The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards completely, parts of the Fortran 2003, 2008 and 2018 standards, and several vendor extensions. The development goal is to provide the following features:

  • Read a user’s program, stored in a file and containing instructions written in Fortran 77, Fortran 90, Fortran 95, Fortran 2003, Fortran 2008 or Fortran 2018. This file contains source code.
  • Translate the user’s program into instructions a computer can carry out more quickly than it takes to translate the instructions in the first place. The result after compilation of a program is machine code, code designed to be efficiently translated and processed by a machine such as your computer. Humans usually are not as good writing machine code as they are at writing Fortran (or C++, Ada, or Java), because it is easy to make tiny mistakes writing machine code.
  • Provide the user with information about the reasons why the compiler is unable to create a binary from the source code. Usually this will be the case if the source code is flawed. The Fortran 90 standard requires that the compiler can point out mistakes to the user. An incorrect usage of the language causes an error message.

    The compiler will also attempt to diagnose cases where the user’s program contains a correct usage of the language, but instructs the computer to do something questionable. This kind of diagnostics message is called a warning message.

  • Provide optional information about the translation passes from the source code to machine code. This can help a user of the compiler to find the cause of certain bugs which may not be obvious in the source code, but may be more easily found at a lower level compiler output. It also helps developers to find bugs in the compiler itself.
  • Provide information in the generated machine code that can make it easier to find bugs in the program (using a debugging tool, called a debugger, such as the GNU Debugger gdb).
  • Locate and gather machine code already generated to perform actions requested by statements in the user’s program. This machine code is organized into modules and is located and linked to the user program.

The GNU Fortran compiler consists of several components:

  • A version of the gcc command (which also might be installed as the system’s cc command) that also understands and accepts Fortran source code. The gcc command is the driver program for all the languages in the GNU Compiler Collection (GCC); With gcc, you can compile the source code of any language for which a front end is available in GCC.
  • The gfortran command itself, which also might be installed as the system’s f95 command. gfortran is just another driver program, but specifically for the Fortran compiler only. The difference with gcc is that gfortran will automatically link the correct libraries to your program.
  • A collection of run-time libraries. These libraries contain the machine code needed to support capabilities of the Fortran language that are not directly provided by the machine code generated by the gfortran compilation phase, such as intrinsic functions and subroutines, and routines for interaction with files and the operating system.
  • The Fortran compiler itself, (f951). This is the GNU Fortran parser and code generator, linked to and interfaced with the GCC backend library. f951 “translates” the source code to assembler code. You would typically not use this program directly; instead, the gcc or gfortran driver programs will call it for you.

1.2 GNU Fortran and GCC

GNU Fortran is a part of GCC, the GNU Compiler Collection. GCC consists of a collection of front ends for various languages, which translate the source code into a language-independent form called GENERIC. This is then processed by a common middle end which provides optimization, and then passed to one of a collection of back ends which generate code for different computer architectures and operating systems.

Functionally, this is implemented with a driver program (gcc) which provides the command-line interface for the compiler. It calls the relevant compiler front-end program (e.g., f951 for Fortran) for each file in the source code, and then calls the assembler and linker as appropriate to produce the compiled output. In a copy of GCC which has been compiled with Fortran language support enabled, gcc will recognize files with .f, .for, .ftn, .f90, .f95, .f03 and .f08 extensions as Fortran source code, and compile it accordingly. A gfortran driver program is also provided, which is identical to gcc except that it automatically links the Fortran runtime libraries into the compiled program.

Source files with .f, .for, .fpp, .ftn, .F, .FOR, .FPP, and .FTN extensions are treated as fixed form. Source files with .f90, .f95, .f03, .f08, .F90, .F95, .F03 and .F08 extensions are treated as free form. The capitalized versions of either form are run through preprocessing. Source files with the lower case .fpp extension are also run through preprocessing.

This manual specifically documents the Fortran front end, which handles the programming language’s syntax and semantics. The aspects of GCC which relate to the optimization passes and the back-end code generation are documented in the GCC manual; see Introduction in Using the GNU Compiler Collection (GCC). The two manuals together provide a complete reference for the GNU Fortran compiler.


1.3 Preprocessing and conditional compilation

Many Fortran compilers including GNU Fortran allow passing the source code through a C preprocessor (CPP; sometimes also called the Fortran preprocessor, FPP) to allow for conditional compilation. In the case of GNU Fortran, this is the GNU C Preprocessor in the traditional mode. On systems with case-preserving file names, the preprocessor is automatically invoked if the filename extension is .F, .FOR, .FTN, .fpp, .FPP, .F90, .F95, .F03 or .F08. To manually invoke the preprocessor on any file, use -cpp, to disable preprocessing on files where the preprocessor is run automatically, use -nocpp.

If a preprocessed file includes another file with the Fortran INCLUDE statement, the included file is not preprocessed. To preprocess included files, use the equivalent preprocessor statement #include.

If GNU Fortran invokes the preprocessor, __GFORTRAN__ is defined. The macros __GNUC__, __GNUC_MINOR__ and __GNUC_PATCHLEVEL__ can be used to determine the version of the compiler. See Overview in The C Preprocessor for details.

GNU Fortran supports a number of INTEGER and REAL kind types in additional to the kind types required by the Fortran standard. The availability of any given kind type is architecture dependent. The following pre-defined preprocessor macros can be used to conditionally include code for these additional kind types: __GFC_INT_1__, __GFC_INT_2__, __GFC_INT_8__, __GFC_INT_16__, __GFC_REAL_10__, and __GFC_REAL_16__.

While CPP is the de-facto standard for preprocessing Fortran code, Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines Conditional Compilation, which is not widely used and not directly supported by the GNU Fortran compiler. You can use the program coco to preprocess such files (http://www.daniellnagle.com/coco.html).


1.4 GNU Fortran and G77

The GNU Fortran compiler is the successor to g77, the Fortran 77 front end included in GCC prior to version 4. It is an entirely new program that has been designed to provide Fortran 95 support and extensibility for future Fortran language standards, as well as providing backwards compatibility for Fortran 77 and nearly all of the GNU language extensions supported by g77.


1.5 Project Status

As soon as gfortran can parse all of the statements correctly, it will be in the “larva” state. When we generate code, the “puppa” state. When gfortran is done, we’ll see if it will be a beautiful butterfly, or just a big bug....

–Andy Vaught, April 2000

The start of the GNU Fortran 95 project was announced on the GCC homepage in March 18, 2000 (even though Andy had already been working on it for a while, of course).

The GNU Fortran compiler is able to compile nearly all standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs, including a number of standard and non-standard extensions, and can be used on real-world programs. In particular, the supported extensions include OpenMP, Cray-style pointers, some old vendor extensions, and several Fortran 2003 and Fortran 2008 features, including TR 15581. However, it is still under development and has a few remaining rough edges. There also is initial support for OpenACC.

At present, the GNU Fortran compiler passes the NIST Fortran 77 Test Suite, and produces acceptable results on the LAPACK Test Suite. It also provides respectable performance on the Polyhedron Fortran compiler benchmarks and the Livermore Fortran Kernels test. It has been used to compile a number of large real-world programs, including the HARMONIE and HIRLAM weather forecasting code and the Tonto quantum chemistry package; see https://gcc.gnu.org/wiki/GfortranApps for an extended list.

Among other things, the GNU Fortran compiler is intended as a replacement for G77. At this point, nearly all programs that could be compiled with G77 can be compiled with GNU Fortran, although there are a few minor known regressions.

The primary work remaining to be done on GNU Fortran falls into three categories: bug fixing (primarily regarding the treatment of invalid code and providing useful error messages), improving the compiler optimizations and the performance of compiled code, and extending the compiler to support future standards—in particular, Fortran 2003, Fortran 2008 and Fortran 2018.


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1.6 Standards

The GNU Fortran compiler implements ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all standard-compliant Fortran 90 and Fortran 77 programs. It also supports the ISO/IEC TR-15581 enhancements to allocatable arrays.

GNU Fortran also have a partial support for ISO/IEC 1539-1:2004 (Fortran 2003), ISO/IEC 1539-1:2010 (Fortran 2008), the Technical Specification Further Interoperability of Fortran with C (ISO/IEC TS 29113:2012). Full support of those standards and future Fortran standards is planned. The current status of the support is can be found in the Fortran 2003 status, Fortran 2008 status and Status of Fortran 2018 support sections of the documentation.

Additionally, the GNU Fortran compilers supports the OpenMP specification (version 4.5 and partial support of the features of the 5.0 version, http://openmp.org/openmp-specifications/). There also is support for the OpenACC specification (targeting version 2.6, http://www.openacc.org/). See https://gcc.gnu.org/wiki/OpenACC for more information.


1.6.1 Varying Length Character Strings

The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000) varying length character strings. While GNU Fortran currently does not support such strings directly, there exist two Fortran implementations for them, which work with GNU Fortran. They can be found at http://www.fortran.com/iso_varying_string.f95 and at ftp://ftp.nag.co.uk/sc22wg5/ISO_VARYING_STRING/.

Deferred-length character strings of Fortran 2003 supports part of the features of ISO_VARYING_STRING and should be considered as replacement. (Namely, allocatable or pointers of the type character(len=:).)


2 GNU Fortran Command Options

The gfortran command supports all the options supported by the gcc command. Only options specific to GNU Fortran are documented here.

See GCC Command Options in Using the GNU Compiler Collection (GCC), for information on the non-Fortran-specific aspects of the gcc command (and, therefore, the gfortran command).

All GCC and GNU Fortran options are accepted both by gfortran and by gcc (as well as any other drivers built at the same time, such as g++), since adding GNU Fortran to the GCC distribution enables acceptance of GNU Fortran options by all of the relevant drivers.

In some cases, options have positive and negative forms; the negative form of -ffoo would be -fno-foo. This manual documents only one of these two forms, whichever one is not the default.


2.1 Option summary

Here is a summary of all the options specific to GNU Fortran, grouped by type. Explanations are in the following sections.

Fortran Language Options

See Options controlling Fortran dialect.

-fall-intrinsics -fallow-argument-mismatch -fallow-invalid-boz 
-fbackslash -fcray-pointer -fd-lines-as-code -fd-lines-as-comments 
-fdec -fdec-char-conversions -fdec-structure -fdec-intrinsic-ints 
-fdec-static -fdec-math -fdec-include -fdec-format-defaults 
-fdec-blank-format-item -fdefault-double-8 -fdefault-integer-8 
-fdefault-real-8 -fdefault-real-10 -fdefault-real-16 -fdollar-ok 
-ffixed-line-length-n -ffixed-line-length-none -fpad-source 
-ffree-form -ffree-line-length-n -ffree-line-length-none 
-fimplicit-none -finteger-4-integer-8 -fmax-identifier-length 
-fmodule-private -ffixed-form -fno-range-check -fopenacc -fopenmp 
-freal-4-real-10 -freal-4-real-16 -freal-4-real-8 -freal-8-real-10 
-freal-8-real-16 -freal-8-real-4 -std=std -ftest-forall-temp

Preprocessing Options

See Enable and customize preprocessing.

-A-question[=answer]
-Aquestion=answer -C -CC -Dmacro[=defn]
-H -P 
-Umacro -cpp -dD -dI -dM -dN -dU -fworking-directory
-imultilib dir 
-iprefix file -iquote -isysroot dir -isystem dir -nocpp 
-nostdinc 
-undef

Error and Warning Options

See Options to request or suppress errors and warnings.

-Waliasing -Wall -Wampersand -Warray-bounds 
-Wc-binding-type -Wcharacter-truncation -Wconversion 
-Wdo-subscript -Wfunction-elimination -Wimplicit-interface 
-Wimplicit-procedure -Wintrinsic-shadow -Wuse-without-only 
-Wintrinsics-std -Wline-truncation -Wno-align-commons 
-Wno-overwrite-recursive -Wno-tabs -Wreal-q-constant -Wsurprising 
-Wunderflow -Wunused-parameter -Wrealloc-lhs -Wrealloc-lhs-all 
-Wfrontend-loop-interchange -Wtarget-lifetime -fmax-errors=n 
-fsyntax-only -pedantic 
-pedantic-errors 

Debugging Options

See Options for debugging your program or GNU Fortran.

-fbacktrace -fdump-fortran-optimized -fdump-fortran-original 
-fdebug-aux-vars -fdump-fortran-global -fdump-parse-tree -ffpe-trap=list 
-ffpe-summary=list

Directory Options

See Options for directory search.

-Idir  -Jdir -fintrinsic-modules-path dir
Link Options

See Options for influencing the linking step.

-static-libgfortran
Runtime Options

See Options for influencing runtime behavior.

-fconvert=conversion -fmax-subrecord-length=length 
-frecord-marker=length -fsign-zero

Interoperability Options

See Options for interoperability.

-fc-prototypes -fc-prototypes-external
Code Generation Options

See Options for code generation conventions.

-faggressive-function-elimination -fblas-matmul-limit=n 
-fbounds-check -ftail-call-workaround -ftail-call-workaround=n 
-fcheck-array-temporaries 
-fcheck=<all|array-temps|bits|bounds|do|mem|pointer|recursion> 
-fcoarray=<none|single|lib> -fexternal-blas -ff2c 
-ffrontend-loop-interchange -ffrontend-optimize 
-finit-character=n -finit-integer=n -finit-local-zero 
-finit-derived -finit-logical=<true|false> 
-finit-real=<zero|inf|-inf|nan|snan>
-finline-matmul-limit=n 
-finline-arg-packing -fmax-array-constructor=n 
-fmax-stack-var-size=n -fno-align-commons -fno-automatic 
-fno-protect-parens -fno-underscoring -fsecond-underscore 
-fpack-derived -frealloc-lhs -frecursive -frepack-arrays 
-fshort-enums -fstack-arrays


2.2 Options controlling Fortran dialect

The following options control the details of the Fortran dialect accepted by the compiler:

-ffree-form
-ffixed-form

Specify the layout used by the source file. The free form layout was introduced in Fortran 90. Fixed form was traditionally used in older Fortran programs. When neither option is specified, the source form is determined by the file extension.

-fall-intrinsics

This option causes all intrinsic procedures (including the GNU-specific extensions) to be accepted. This can be useful with -std=f95 to force standard-compliance but get access to the full range of intrinsics available with gfortran. As a consequence, -Wintrinsics-std will be ignored and no user-defined procedure with the same name as any intrinsic will be called except when it is explicitly declared EXTERNAL.

-fallow-argument-mismatch

Some code contains calls to external procedures with mismatches between the calls and the procedure definition, or with mismatches between different calls. Such code is non-conforming, and will usually be flagged with an error. This options degrades the error to a warning, which can only be disabled by disabling all warnings via -w. Only a single occurrence per argument is flagged by this warning. -fallow-argument-mismatch is implied by -std=legacy.

Using this option is strongly discouraged. It is possible to provide standard-conforming code which allows different types of arguments by using an explicit interface and TYPE(*).

-fallow-invalid-boz

A BOZ literal constant can occur in a limited number of contexts in standard conforming Fortran. This option degrades an error condition to a warning, and allows a BOZ literal constant to appear where the Fortran standard would otherwise prohibit its use.

-fd-lines-as-code
-fd-lines-as-comments

Enable special treatment for lines beginning with d or D in fixed form sources. If the -fd-lines-as-code option is given they are treated as if the first column contained a blank. If the -fd-lines-as-comments option is given, they are treated as comment lines.

-fdec

DEC compatibility mode. Enables extensions and other features that mimic the default behavior of older compilers (such as DEC). These features are non-standard and should be avoided at all costs. For details on GNU Fortran’s implementation of these extensions see the full documentation.

Other flags enabled by this switch are: -fdollar-ok -fcray-pointer -fdec-char-conversions -fdec-structure -fdec-intrinsic-ints -fdec-static -fdec-math -fdec-include -fdec-blank-format-item -fdec-format-defaults

If -fd-lines-as-code/-fd-lines-as-comments are unset, then -fdec also sets -fd-lines-as-comments.

-fdec-char-conversions

Enable the use of character literals in assignments and DATA statements for non-character variables.

-fdec-structure

Enable DEC STRUCTURE and RECORD as well as UNION, MAP, and dot (’.’) as a member separator (in addition to ’%’). This is provided for compatibility only; Fortran 90 derived types should be used instead where possible.

-fdec-intrinsic-ints

Enable B/I/J/K kind variants of existing integer functions (e.g. BIAND, IIAND, JIAND, etc...). For a complete list of intrinsics see the full documentation.

-fdec-math

Enable legacy math intrinsics such as COTAN and degree-valued trigonometric functions (e.g. TAND, ATAND, etc...) for compatability with older code.

-fdec-static

Enable DEC-style STATIC and AUTOMATIC attributes to explicitly specify the storage of variables and other objects.

-fdec-include

Enable parsing of INCLUDE as a statement in addition to parsing it as INCLUDE line. When parsed as INCLUDE statement, INCLUDE does not have to be on a single line and can use line continuations.

-fdec-format-defaults

Enable format specifiers F, G and I to be used without width specifiers, default widths will be used instead.

-fdec-blank-format-item

Enable a blank format item at the end of a format specification i.e. nothing following the final comma.

-fdollar-ok

Allow ‘$’ as a valid non-first character in a symbol name. Symbols that start with ‘$’ are rejected since it is unclear which rules to apply to implicit typing as different vendors implement different rules. Using ‘$’ in IMPLICIT statements is also rejected.

-fbackslash

Change the interpretation of backslashes in string literals from a single backslash character to “C-style” escape characters. The following combinations are expanded \a, \b, \f, \n, \r, \t, \v, \\, and \0 to the ASCII characters alert, backspace, form feed, newline, carriage return, horizontal tab, vertical tab, backslash, and NUL, respectively. Additionally, \xnn, \unnnn and \Unnnnnnnn (where each n is a hexadecimal digit) are translated into the Unicode characters corresponding to the specified code points. All other combinations of a character preceded by \ are unexpanded.

-fmodule-private

Set the default accessibility of module entities to PRIVATE. Use-associated entities will not be accessible unless they are explicitly declared as PUBLIC.

-ffixed-line-length-n

Set column after which characters are ignored in typical fixed-form lines in the source file, and, unless -fno-pad-source, through which spaces are assumed (as if padded to that length) after the ends of short fixed-form lines.

Popular values for n include 72 (the standard and the default), 80 (card image), and 132 (corresponding to “extended-source” options in some popular compilers). n may also be ‘none’, meaning that the entire line is meaningful and that continued character constants never have implicit spaces appended to them to fill out the line. -ffixed-line-length-0 means the same thing as -ffixed-line-length-none.

-fno-pad-source

By default fixed-form lines have spaces assumed (as if padded to that length) after the ends of short fixed-form lines. This is not done either if -ffixed-line-length-0, -ffixed-line-length-none or if -fno-pad-source option is used. With any of those options continued character constants never have implicit spaces appended to them to fill out the line.

-ffree-line-length-n

Set column after which characters are ignored in typical free-form lines in the source file. The default value is 132. n may be ‘none’, meaning that the entire line is meaningful. -ffree-line-length-0 means the same thing as -ffree-line-length-none.

-fmax-identifier-length=n

Specify the maximum allowed identifier length. Typical values are 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008).

-fimplicit-none

Specify that no implicit typing is allowed, unless overridden by explicit IMPLICIT statements. This is the equivalent of adding implicit none to the start of every procedure.

-fcray-pointer

Enable the Cray pointer extension, which provides C-like pointer functionality.

-fopenacc

Enable the OpenACC extensions. This includes OpenACC !$acc directives in free form and c$acc, *$acc and !$acc directives in fixed form, !$ conditional compilation sentinels in free form and c$, *$ and !$ sentinels in fixed form, and when linking arranges for the OpenACC runtime library to be linked in.

-fopenmp

Enable the OpenMP extensions. This includes OpenMP !$omp directives in free form and c$omp, *$omp and !$omp directives in fixed form, !$ conditional compilation sentinels in free form and c$, *$ and !$ sentinels in fixed form, and when linking arranges for the OpenMP runtime library to be linked in. The option -fopenmp implies -frecursive.

-fno-range-check

Disable range checking on results of simplification of constant expressions during compilation. For example, GNU Fortran will give an error at compile time when simplifying a = 1. / 0. With this option, no error will be given and a will be assigned the value +Infinity. If an expression evaluates to a value outside of the relevant range of [-HUGE():HUGE()], then the expression will be replaced by -Inf or +Inf as appropriate. Similarly, DATA i/Z'FFFFFFFF'/ will result in an integer overflow on most systems, but with -fno-range-check the value will “wrap around” and i will be initialized to -1 instead.

-fdefault-integer-8

Set the default integer and logical types to an 8 byte wide type. This option also affects the kind of integer constants like 42. Unlike -finteger-4-integer-8, it does not promote variables with explicit kind declaration.

-fdefault-real-8

Set the default real type to an 8 byte wide type. This option also affects the kind of non-double real constants like 1.0. This option promotes the default width of DOUBLE PRECISION and double real constants like 1.d0 to 16 bytes if possible. If -fdefault-double-8 is given along with fdefault-real-8, DOUBLE PRECISION and double real constants are not promoted. Unlike -freal-4-real-8, fdefault-real-8 does not promote variables with explicit kind declarations.

-fdefault-real-10

Set the default real type to an 10 byte wide type. This option also affects the kind of non-double real constants like 1.0. This option promotes the default width of DOUBLE PRECISION and double real constants like 1.d0 to 16 bytes if possible. If -fdefault-double-8 is given along with fdefault-real-10, DOUBLE PRECISION and double real constants are not promoted. Unlike -freal-4-real-10, fdefault-real-10 does not promote variables with explicit kind declarations.

-fdefault-real-16

Set the default real type to an 16 byte wide type. This option also affects the kind of non-double real constants like 1.0. This option promotes the default width of DOUBLE PRECISION and double real constants like 1.d0 to 16 bytes if possible. If -fdefault-double-8 is given along with fdefault-real-16, DOUBLE PRECISION and double real constants are not promoted. Unlike -freal-4-real-16, fdefault-real-16 does not promote variables with explicit kind declarations.

-fdefault-double-8

Set the DOUBLE PRECISION type and double real constants like 1.d0 to an 8 byte wide type. Do nothing if this is already the default. This option prevents -fdefault-real-8, -fdefault-real-10, and -fdefault-real-16, from promoting DOUBLE PRECISION and double real constants like 1.d0 to 16 bytes.

-finteger-4-integer-8

Promote all INTEGER(KIND=4) entities to an INTEGER(KIND=8) entities. If KIND=8 is unavailable, then an error will be issued. This option should be used with care and may not be suitable for your codes. Areas of possible concern include calls to external procedures, alignment in EQUIVALENCE and/or COMMON, generic interfaces, BOZ literal constant conversion, and I/O. Inspection of the intermediate representation of the translated Fortran code, produced by -fdump-tree-original, is suggested.

-freal-4-real-8
-freal-4-real-10
-freal-4-real-16
-freal-8-real-4
-freal-8-real-10
-freal-8-real-16

Promote all REAL(KIND=M) entities to REAL(KIND=N) entities. If REAL(KIND=N) is unavailable, then an error will be issued. The -freal-4- flags also affect the default real kind and the -freal-8- flags also the double-precision real kind. All other real-kind types are unaffected by this option. The promotion is also applied to real literal constants of default and double-precision kind and a specified kind number of 4 or 8, respectively. However, -fdefault-real-8, -fdefault-real-10, -fdefault-real-10, and -fdefault-double-8 take precedence for the default and double-precision real kinds, both for real literal constants and for declarations without a kind number. Note that for REAL(KIND=KIND(1.0)) the literal may get promoted and then the result may get promoted again. These options should be used with care and may not be suitable for your codes. Areas of possible concern include calls to external procedures, alignment in EQUIVALENCE and/or COMMON, generic interfaces, BOZ literal constant conversion, and I/O and calls to intrinsic procedures when passing a value to the kind= dummy argument. Inspection of the intermediate representation of the translated Fortran code, produced by -fdump-fortran-original or -fdump-tree-original, is suggested.

-std=std

Specify the standard to which the program is expected to conform, which may be one of ‘f95’, ‘f2003’, ‘f2008’, ‘f2018’, ‘gnu’, or ‘legacy’. The default value for std is ‘gnu’, which specifies a superset of the latest Fortran standard that includes all of the extensions supported by GNU Fortran, although warnings will be given for obsolete extensions not recommended for use in new code. The ‘legacy’ value is equivalent but without the warnings for obsolete extensions, and may be useful for old non-standard programs. The ‘f95’, ‘f2003’, ‘f2008’, and ‘f2018’ values specify strict conformance to the Fortran 95, Fortran 2003, Fortran 2008 and Fortran 2018 standards, respectively; errors are given for all extensions beyond the relevant language standard, and warnings are given for the Fortran 77 features that are permitted but obsolescent in later standards. The deprecated option ‘-std=f2008ts’ acts as an alias for ‘-std=f2018’. It is only present for backwards compatibility with earlier gfortran versions and should not be used any more.

-ftest-forall-temp

Enhance test coverage by forcing most forall assignments to use temporary.


2.3 Enable and customize preprocessing

Preprocessor related options. See section Preprocessing and conditional compilation for more detailed information on preprocessing in gfortran.

-cpp
-nocpp

Enable preprocessing. The preprocessor is automatically invoked if the file extension is .fpp, .FPP, .F, .FOR, .FTN, .F90, .F95, .F03 or .F08. Use this option to manually enable preprocessing of any kind of Fortran file.

To disable preprocessing of files with any of the above listed extensions, use the negative form: -nocpp.

The preprocessor is run in traditional mode. Any restrictions of the file-format, especially the limits on line length, apply for preprocessed output as well, so it might be advisable to use the -ffree-line-length-none or -ffixed-line-length-none options.

-dM

Instead of the normal output, generate a list of '#define' directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a way of finding out what is predefined in your version of the preprocessor. Assuming you have no file foo.f90, the command

  touch foo.f90; gfortran -cpp -E -dM foo.f90

will show all the predefined macros.

-dD

Like -dM except in two respects: it does not include the predefined macros, and it outputs both the #define directives and the result of preprocessing. Both kinds of output go to the standard output file.

-dN

Like -dD, but emit only the macro names, not their expansions.

-dU

Like dD except that only macros that are expanded, or whose definedness is tested in preprocessor directives, are output; the output is delayed until the use or test of the macro; and '#undef' directives are also output for macros tested but undefined at the time.

-dI

Output '#include' directives in addition to the result of preprocessing.

-fworking-directory

Enable generation of linemarkers in the preprocessor output that will let the compiler know the current working directory at the time of preprocessing. When this option is enabled, the preprocessor will emit, after the initial linemarker, a second linemarker with the current working directory followed by two slashes. GCC will use this directory, when it is present in the preprocessed input, as the directory emitted as the current working directory in some debugging information formats. This option is implicitly enabled if debugging information is enabled, but this can be inhibited with the negated form -fno-working-directory. If the -P flag is present in the command line, this option has no effect, since no #line directives are emitted whatsoever.

-idirafter dir

Search dir for include files, but do it after all directories specified with -I and the standard system directories have been exhausted. dir is treated as a system include directory. If dir begins with =, then the = will be replaced by the sysroot prefix; see --sysroot and -isysroot.

-imultilib dir

Use dir as a subdirectory of the directory containing target-specific C++ headers.

-iprefix prefix

Specify prefix as the prefix for subsequent -iwithprefix options. If the prefix represents a directory, you should include the final '/'.

-isysroot dir

This option is like the --sysroot option, but applies only to header files. See the --sysroot option for more information.

-iquote dir

Search dir only for header files requested with #include "file"; they are not searched for #include <file>, before all directories specified by -I and before the standard system directories. If dir begins with =, then the = will be replaced by the sysroot prefix; see --sysroot and -isysroot.

-isystem dir

Search dir for header files, after all directories specified by -I but before the standard system directories. Mark it as a system directory, so that it gets the same special treatment as is applied to the standard system directories. If dir begins with =, then the = will be replaced by the sysroot prefix; see --sysroot and -isysroot.

-nostdinc

Do not search the standard system directories for header files. Only the directories you have specified with -I options (and the directory of the current file, if appropriate) are searched.

-undef

Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined.

-Apredicate=answer

Make an assertion with the predicate predicate and answer answer. This form is preferred to the older form -A predicate(answer), which is still supported, because it does not use shell special characters.

-A-predicate=answer

Cancel an assertion with the predicate predicate and answer answer.

-C

Do not discard comments. All comments are passed through to the output file, except for comments in processed directives, which are deleted along with the directive.

You should be prepared for side effects when using -C; it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a '#'.

Warning: this currently handles C-Style comments only. The preprocessor does not yet recognize Fortran-style comments.

-CC

Do not discard comments, including during macro expansion. This is like -C, except that comments contained within macros are also passed through to the output file where the macro is expanded.

In addition to the side-effects of the -C option, the -CC option causes all C++-style comments inside a macro to be converted to C-style comments. This is to prevent later use of that macro from inadvertently commenting out the remainder of the source line. The -CC option is generally used to support lint comments.

Warning: this currently handles C- and C++-Style comments only. The preprocessor does not yet recognize Fortran-style comments.

-Dname

Predefine name as a macro, with definition 1.

-Dname=definition

The contents of definition are tokenized and processed as if they appeared during translation phase three in a '#define' directive. In particular, the definition will be truncated by embedded newline characters.

If you are invoking the preprocessor from a shell or shell-like program you may need to use the shell’s quoting syntax to protect characters such as spaces that have a meaning in the shell syntax.

If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most shells, so you will need to quote the option. With sh and csh, -D'name(args...)=definition' works.

-D and -U options are processed in the order they are given on the command line. All -imacros file and -include file options are processed after all -D and -U options.

-H

Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the '#include' stack it is.

-P

Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program which might be confused by the linemarkers.

-Uname

Cancel any previous definition of name, either built in or provided with a -D option.


2.4 Options to request or suppress errors and warnings

Errors are diagnostic messages that report that the GNU Fortran compiler cannot compile the relevant piece of source code. The compiler will continue to process the program in an attempt to report further errors to aid in debugging, but will not produce any compiled output.

Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there is likely to be a bug in the program. Unless -Werror is specified, they do not prevent compilation of the program.

You can request many specific warnings with options beginning -W, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning -Wno- to turn off warnings; for example, -Wno-implicit. This manual lists only one of the two forms, whichever is not the default.

These options control the amount and kinds of errors and warnings produced by GNU Fortran:

-fmax-errors=n

Limits the maximum number of error messages to n, at which point GNU Fortran bails out rather than attempting to continue processing the source code. If n is 0, there is no limit on the number of error messages produced.

-fsyntax-only

Check the code for syntax errors, but do not actually compile it. This will generate module files for each module present in the code, but no other output file.

-Wpedantic
-pedantic

Issue warnings for uses of extensions to Fortran. -pedantic also applies to C-language constructs where they occur in GNU Fortran source files, such as use of ‘\e’ in a character constant within a directive like #include.

Valid Fortran programs should compile properly with or without this option. However, without this option, certain GNU extensions and traditional Fortran features are supported as well. With this option, many of them are rejected.

Some users try to use -pedantic to check programs for conformance. They soon find that it does not do quite what they want—it finds some nonstandard practices, but not all. However, improvements to GNU Fortran in this area are welcome.

This should be used in conjunction with -std=f95, -std=f2003, -std=f2008 or -std=f2018.

-pedantic-errors

Like -pedantic, except that errors are produced rather than warnings.

-Wall

Enables commonly used warning options pertaining to usage that we recommend avoiding and that we believe are easy to avoid. This currently includes -Waliasing, -Wampersand, -Wconversion, -Wsurprising, -Wc-binding-type, -Wintrinsics-std, -Wtabs, -Wintrinsic-shadow, -Wline-truncation, -Wtarget-lifetime, -Winteger-division, -Wreal-q-constant, -Wunused and -Wundefined-do-loop.

-Waliasing

Warn about possible aliasing of dummy arguments. Specifically, it warns if the same actual argument is associated with a dummy argument with INTENT(IN) and a dummy argument with INTENT(OUT) in a call with an explicit interface.

The following example will trigger the warning.

  interface
    subroutine bar(a,b)
      integer, intent(in) :: a
      integer, intent(out) :: b
    end subroutine
  end interface
  integer :: a

  call bar(a,a)
-Wampersand

Warn about missing ampersand in continued character constants. The warning is given with -Wampersand, -pedantic, -std=f95, -std=f2003, -std=f2008 and -std=f2018. Note: With no ampersand given in a continued character constant, GNU Fortran assumes continuation at the first non-comment, non-whitespace character after the ampersand that initiated the continuation.

-Warray-temporaries

Warn about array temporaries generated by the compiler. The information generated by this warning is sometimes useful in optimization, in order to avoid such temporaries.

-Wc-binding-type

Warn if the a variable might not be C interoperable. In particular, warn if the variable has been declared using an intrinsic type with default kind instead of using a kind parameter defined for C interoperability in the intrinsic ISO_C_Binding module. This option is implied by -Wall.

-Wcharacter-truncation

Warn when a character assignment will truncate the assigned string.

-Wline-truncation

Warn when a source code line will be truncated. This option is implied by -Wall. For free-form source code, the default is -Werror=line-truncation such that truncations are reported as error.

-Wconversion

Warn about implicit conversions that are likely to change the value of the expression after conversion. Implied by -Wall.

-Wconversion-extra

Warn about implicit conversions between different types and kinds. This option does not imply -Wconversion.

-Wextra

Enables some warning options for usages of language features which may be problematic. This currently includes -Wcompare-reals, -Wunused-parameter and -Wdo-subscript.

-Wfrontend-loop-interchange

Warn when using -ffrontend-loop-interchange for performing loop interchanges.

-Wimplicit-interface

Warn if a procedure is called without an explicit interface. Note this only checks that an explicit interface is present. It does not check that the declared interfaces are consistent across program units.

-Wimplicit-procedure

Warn if a procedure is called that has neither an explicit interface nor has been declared as EXTERNAL.

-Winteger-division

Warn if a constant integer division truncates its result. As an example, 3/5 evaluates to 0.

-Wintrinsics-std

Warn if gfortran finds a procedure named like an intrinsic not available in the currently selected standard (with -std) and treats it as EXTERNAL procedure because of this. -fall-intrinsics can be used to never trigger this behavior and always link to the intrinsic regardless of the selected standard.

-Wno-overwrite-recursive

Do not warn when -fno-automatic is used with -frecursive. Recursion will be broken if the relevant local variables do not have the attribute AUTOMATIC explicitly declared. This option can be used to suppress the warning when it is known that recursion is not broken. Useful for build environments that use -Werror.

-Wreal-q-constant

Produce a warning if a real-literal-constant contains a q exponent-letter.

-Wsurprising

Produce a warning when “suspicious” code constructs are encountered. While technically legal these usually indicate that an error has been made.

This currently produces a warning under the following circumstances:

  • An INTEGER SELECT construct has a CASE that can never be matched as its lower value is greater than its upper value.
  • A LOGICAL SELECT construct has three CASE statements.
  • A TRANSFER specifies a source that is shorter than the destination.
  • The type of a function result is declared more than once with the same type. If -pedantic or standard-conforming mode is enabled, this is an error.
  • A CHARACTER variable is declared with negative length.
-Wtabs

By default, tabs are accepted as whitespace, but tabs are not members of the Fortran Character Set. For continuation lines, a tab followed by a digit between 1 and 9 is supported. -Wtabs will cause a warning to be issued if a tab is encountered. Note, -Wtabs is active for -pedantic, -std=f95, -std=f2003, -std=f2008, -std=f2018 and -Wall.

-Wundefined-do-loop

Warn if a DO loop with step either 1 or -1 yields an underflow or an overflow during iteration of an induction variable of the loop. This option is implied by -Wall.

-Wunderflow

Produce a warning when numerical constant expressions are encountered, which yield an UNDERFLOW during compilation. Enabled by default.

-Wintrinsic-shadow

Warn if a user-defined procedure or module procedure has the same name as an intrinsic; in this case, an explicit interface or EXTERNAL or INTRINSIC declaration might be needed to get calls later resolved to the desired intrinsic/procedure. This option is implied by -Wall.

-Wuse-without-only

Warn if a USE statement has no ONLY qualifier and thus implicitly imports all public entities of the used module.

-Wunused-dummy-argument

Warn about unused dummy arguments. This option is implied by -Wall.

-Wunused-parameter

Contrary to gcc’s meaning of -Wunused-parameter, gfortran’s implementation of this option does not warn about unused dummy arguments (see -Wunused-dummy-argument), but about unused PARAMETER values. -Wunused-parameter is implied by -Wextra if also -Wunused or -Wall is used.

-Walign-commons

By default, gfortran warns about any occasion of variables being padded for proper alignment inside a COMMON block. This warning can be turned off via -Wno-align-commons. See also -falign-commons.

-Wfunction-elimination

Warn if any calls to impure functions are eliminated by the optimizations enabled by the -ffrontend-optimize option. This option is implied by -Wextra.

-Wrealloc-lhs

Warn when the compiler might insert code to for allocation or reallocation of an allocatable array variable of intrinsic type in intrinsic assignments. In hot loops, the Fortran 2003 reallocation feature may reduce the performance. If the array is already allocated with the correct shape, consider using a whole-array array-spec (e.g. (:,:,:)) for the variable on the left-hand side to prevent the reallocation check. Note that in some cases the warning is shown, even if the compiler will optimize reallocation checks away. For instance, when the right-hand side contains the same variable multiplied by a scalar. See also -frealloc-lhs.

-Wrealloc-lhs-all

Warn when the compiler inserts code to for allocation or reallocation of an allocatable variable; this includes scalars and derived types.

-Wcompare-reals

Warn when comparing real or complex types for equality or inequality. This option is implied by -Wextra.

-Wtarget-lifetime

Warn if the pointer in a pointer assignment might be longer than the its target. This option is implied by -Wall.

-Wzerotrip

Warn if a DO loop is known to execute zero times at compile time. This option is implied by -Wall.

-Wdo-subscript

Warn if an array subscript inside a DO loop could lead to an out-of-bounds access even if the compiler cannot prove that the statement is actually executed, in cases like

  real a(3)
  do i=1,4
    if (condition(i)) then
      a(i) = 1.2
    end if
  end do

This option is implied by -Wextra.

-Werror

Turns all warnings into errors.

See Options to Request or Suppress Errors and Warnings in Using the GNU Compiler Collection (GCC), for information on more options offered by the GBE shared by gfortran, gcc and other GNU compilers.

Some of these have no effect when compiling programs written in Fortran.


2.5 Options for debugging your program or GNU Fortran

GNU Fortran has various special options that are used for debugging either your program or the GNU Fortran compiler.

-fdump-fortran-original

Output the internal parse tree after translating the source program into internal representation. This option is mostly useful for debugging the GNU Fortran compiler itself. The output generated by this option might change between releases. This option may also generate internal compiler errors for features which have only recently been added.

-fdump-fortran-optimized

Output the parse tree after front-end optimization. Mostly useful for debugging the GNU Fortran compiler itself. The output generated by this option might change between releases. This option may also generate internal compiler errors for features which have only recently been added.

-fdump-parse-tree

Output the internal parse tree after translating the source program into internal representation. Mostly useful for debugging the GNU Fortran compiler itself. The output generated by this option might change between releases. This option may also generate internal compiler errors for features which have only recently been added. This option is deprecated; use -fdump-fortran-original instead.

-fdebug-aux-vars

Renames internal variables created by the gfortran front end and makes them accessible to a debugger. The name of the internal variables then start with upper-case letters followed by an underscore. This option is useful for debugging the compiler’s code generation together with -fdump-tree-original and enabling debugging of the executable program by using -g or -ggdb3.

-fdump-fortran-global

Output a list of the global identifiers after translating into middle-end representation. Mostly useful for debugging the GNU Fortran compiler itself. The output generated by this option might change between releases. This option may also generate internal compiler errors for features which have only recently been added.

-ffpe-trap=list

Specify a list of floating point exception traps to enable. On most systems, if a floating point exception occurs and the trap for that exception is enabled, a SIGFPE signal will be sent and the program being aborted, producing a core file useful for debugging. list is a (possibly empty) comma-separated list of the following exceptions: ‘invalid’ (invalid floating point operation, such as SQRT(-1.0)), ‘zero’ (division by zero), ‘overflow’ (overflow in a floating point operation), ‘underflow’ (underflow in a floating point operation), ‘inexact’ (loss of precision during operation), and ‘denormal’ (operation performed on a denormal value). The first five exceptions correspond to the five IEEE 754 exceptions, whereas the last one (‘denormal’) is not part of the IEEE 754 standard but is available on some common architectures such as x86.

The first three exceptions (‘invalid’, ‘zero’, and ‘overflow’) often indicate serious errors, and unless the program has provisions for dealing with these exceptions, enabling traps for these three exceptions is probably a good idea.

If the option is used more than once in the command line, the lists will be joined: ’ffpe-trap=list1 ffpe-trap=list2’ is equivalent to ffpe-trap=list1,list2.

Note that once enabled an exception cannot be disabled (no negative form).

Many, if not most, floating point operations incur loss of precision due to rounding, and hence the ffpe-trap=inexact is likely to be uninteresting in practice.

By default no exception traps are enabled.

-ffpe-summary=list

Specify a list of floating-point exceptions, whose flag status is printed to ERROR_UNIT when invoking STOP and ERROR STOP. list can be either ‘none’, ‘all’ or a comma-separated list of the following exceptions: ‘invalid’, ‘zero’, ‘overflow’, ‘underflow’, ‘inexact’ and ‘denormal’. (See -ffpe-trap for a description of the exceptions.)

If the option is used more than once in the command line, only the last one will be used.

By default, a summary for all exceptions but ‘inexact’ is shown.

-fno-backtrace

When a serious runtime error is encountered or a deadly signal is emitted (segmentation fault, illegal instruction, bus error, floating-point exception, and the other POSIX signals that have the action ‘core’), the Fortran runtime library tries to output a backtrace of the error. -fno-backtrace disables the backtrace generation. This option only has influence for compilation of the Fortran main program.

See Options for Debugging Your Program or GCC in Using the GNU Compiler Collection (GCC), for more information on debugging options.


2.6 Options for directory search

These options affect how GNU Fortran searches for files specified by the INCLUDE directive and where it searches for previously compiled modules.

It also affects the search paths used by cpp when used to preprocess Fortran source.

-Idir

These affect interpretation of the INCLUDE directive (as well as of the #include directive of the cpp preprocessor).

Also note that the general behavior of -I and INCLUDE is pretty much the same as of -I with #include in the cpp preprocessor, with regard to looking for header.gcc files and other such things.

This path is also used to search for .mod files when previously compiled modules are required by a USE statement.

See Options for Directory Search in Using the GNU Compiler Collection (GCC), for information on the -I option.

-Jdir

This option specifies where to put .mod files for compiled modules. It is also added to the list of directories to searched by an USE statement.

The default is the current directory.

-fintrinsic-modules-path dir

This option specifies the location of pre-compiled intrinsic modules, if they are not in the default location expected by the compiler.


2.8 Influencing runtime behavior

These options affect the runtime behavior of programs compiled with GNU Fortran.

-fconvert=conversion

Specify the representation of data for unformatted files. Valid values for conversion are: ‘native’, the default; ‘swap’, swap between big- and little-endian; ‘big-endian’, use big-endian representation for unformatted files; ‘little-endian’, use little-endian representation for unformatted files.

This option has an effect only when used in the main program. The CONVERT specifier and the GFORTRAN_CONVERT_UNIT environment variable override the default specified by -fconvert.

-frecord-marker=length

Specify the length of record markers for unformatted files. Valid values for length are 4 and 8. Default is 4. This is different from previous versions of gfortran, which specified a default record marker length of 8 on most systems. If you want to read or write files compatible with earlier versions of gfortran, use -frecord-marker=8.

-fmax-subrecord-length=length

Specify the maximum length for a subrecord. The maximum permitted value for length is 2147483639, which is also the default. Only really useful for use by the gfortran testsuite.

-fsign-zero

When enabled, floating point numbers of value zero with the sign bit set are written as negative number in formatted output and treated as negative in the SIGN intrinsic. -fno-sign-zero does not print the negative sign of zero values (or values rounded to zero for I/O) and regards zero as positive number in the SIGN intrinsic for compatibility with Fortran 77. The default is -fsign-zero.


2.9 Options for code generation conventions

These machine-independent options control the interface conventions used in code generation.

Most of them have both positive and negative forms; the negative form of -ffoo would be -fno-foo. In the table below, only one of the forms is listed—the one which is not the default. You can figure out the other form by either removing no- or adding it.

-fno-automatic

Treat each program unit (except those marked as RECURSIVE) as if the SAVE statement were specified for every local variable and array referenced in it. Does not affect common blocks. (Some Fortran compilers provide this option under the name -static or -save.) The default, which is -fautomatic, uses the stack for local variables smaller than the value given by -fmax-stack-var-size. Use the option -frecursive to use no static memory.

Local variables or arrays having an explicit SAVE attribute are silently ignored unless the -pedantic option is added.

-ff2c

Generate code designed to be compatible with code generated by g77 and f2c.

The calling conventions used by g77 (originally implemented in f2c) require functions that return type default REAL to actually return the C type double, and functions that return type COMPLEX to return the values via an extra argument in the calling sequence that points to where to store the return value. Under the default GNU calling conventions, such functions simply return their results as they would in GNU C—default REAL functions return the C type float, and COMPLEX functions return the GNU C type complex. Additionally, this option implies the -fsecond-underscore option, unless -fno-second-underscore is explicitly requested.

This does not affect the generation of code that interfaces with the libgfortran library.

Caution: It is not a good idea to mix Fortran code compiled with -ff2c with code compiled with the default -fno-f2c calling conventions as, calling COMPLEX or default REAL functions between program parts which were compiled with different calling conventions will break at execution time.

Caution: This will break code which passes intrinsic functions of type default REAL or COMPLEX as actual arguments, as the library implementations use the -fno-f2c calling conventions.

-fno-underscoring

Do not transform names of entities specified in the Fortran source file by appending underscores to them.

With -funderscoring in effect, GNU Fortran appends one underscore to external names with no underscores. This is done to ensure compatibility with code produced by many UNIX Fortran compilers.

Caution: The default behavior of GNU Fortran is incompatible with f2c and g77, please use the -ff2c option if you want object files compiled with GNU Fortran to be compatible with object code created with these tools.

Use of -fno-underscoring is not recommended unless you are experimenting with issues such as integration of GNU Fortran into existing system environments (vis-à-vis existing libraries, tools, and so on).

For example, with -funderscoring, and assuming that j() and max_count() are external functions while my_var and lvar are local variables, a statement like

I = J() + MAX_COUNT (MY_VAR, LVAR)

is implemented as something akin to:

i = j_() + max_count__(&my_var__, &lvar);

With -fno-underscoring, the same statement is implemented as:

i = j() + max_count(&my_var, &lvar);

Use of -fno-underscoring allows direct specification of user-defined names while debugging and when interfacing GNU Fortran code with other languages.

Note that just because the names match does not mean that the interface implemented by GNU Fortran for an external name matches the interface implemented by some other language for that same name. That is, getting code produced by GNU Fortran to link to code produced by some other compiler using this or any other method can be only a small part of the overall solution—getting the code generated by both compilers to agree on issues other than naming can require significant effort, and, unlike naming disagreements, linkers normally cannot detect disagreements in these other areas.

Also, note that with -fno-underscoring, the lack of appended underscores introduces the very real possibility that a user-defined external name will conflict with a name in a system library, which could make finding unresolved-reference bugs quite difficult in some cases—they might occur at program run time, and show up only as buggy behavior at run time.

In future versions of GNU Fortran we hope to improve naming and linking issues so that debugging always involves using the names as they appear in the source, even if the names as seen by the linker are mangled to prevent accidental linking between procedures with incompatible interfaces.

-fsecond-underscore

By default, GNU Fortran appends an underscore to external names. If this option is used GNU Fortran appends two underscores to names with underscores and one underscore to external names with no underscores. GNU Fortran also appends two underscores to internal names with underscores to avoid naming collisions with external names.

This option has no effect if -fno-underscoring is in effect. It is implied by the -ff2c option.

Otherwise, with this option, an external name such as MAX_COUNT is implemented as a reference to the link-time external symbol max_count__, instead of max_count_. This is required for compatibility with g77 and f2c, and is implied by use of the -ff2c option.

-fcoarray=<keyword>
none

Disable coarray support; using coarray declarations and image-control statements will produce a compile-time error. (Default)

single

Single-image mode, i.e. num_images() is always one.

lib

Library-based coarray parallelization; a suitable GNU Fortran coarray library needs to be linked.

-fcheck=<keyword>

Enable the generation of run-time checks; the argument shall be a comma-delimited list of the following keywords. Prefixing a check with no- disables it if it was activated by a previous specification.

all

Enable all run-time test of -fcheck.

array-temps

Warns at run time when for passing an actual argument a temporary array had to be generated. The information generated by this warning is sometimes useful in optimization, in order to avoid such temporaries.

Note: The warning is only printed once per location.

bits

Enable generation of run-time checks for invalid arguments to the bit manipulation intrinsics.

bounds

Enable generation of run-time checks for array subscripts and against the declared minimum and maximum values. It also checks array indices for assumed and deferred shape arrays against the actual allocated bounds and ensures that all string lengths are equal for character array constructors without an explicit typespec.

Some checks require that -fcheck=bounds is set for the compilation of the main program.

Note: In the future this may also include other forms of checking, e.g., checking substring references.

do

Enable generation of run-time checks for invalid modification of loop iteration variables.

mem

Enable generation of run-time checks for memory allocation. Note: This option does not affect explicit allocations using the ALLOCATE statement, which will be always checked.

pointer

Enable generation of run-time checks for pointers and allocatables.

recursion

Enable generation of run-time checks for recursively called subroutines and functions which are not marked as recursive. See also -frecursive. Note: This check does not work for OpenMP programs and is disabled if used together with -frecursive and -fopenmp.

Example: Assuming you have a file foo.f90, the command

  gfortran -fcheck=all,no-array-temps foo.f90

will compile the file with all checks enabled as specified above except warnings for generated array temporaries.

-fbounds-check

Deprecated alias for -fcheck=bounds.

-ftail-call-workaround
-ftail-call-workaround=n

Some C interfaces to Fortran codes violate the gfortran ABI by omitting the hidden character length arguments as described in See Argument passing conventions. This can lead to crashes because pushing arguments for tail calls can overflow the stack.

To provide a workaround for existing binary packages, this option disables tail call optimization for gfortran procedures with character arguments. With -ftail-call-workaround=2 tail call optimization is disabled in all gfortran procedures with character arguments, with -ftail-call-workaround=1 or equivalent -ftail-call-workaround only in gfortran procedures with character arguments that call implicitly prototyped procedures.

Using this option can lead to problems including crashes due to insufficient stack space.

It is very strongly recommended to fix the code in question. The -fc-prototypes-external option can be used to generate prototypes which conform to gfortran’s ABI, for inclusion in the source code.

Support for this option will likely be withdrawn in a future release of gfortran.

The negative form, -fno-tail-call-workaround or equivalent -ftail-call-workaround=0, can be used to disable this option.

Default is currently -ftail-call-workaround, this will change in future releases.

-fcheck-array-temporaries

Deprecated alias for -fcheck=array-temps.

-fmax-array-constructor=n

This option can be used to increase the upper limit permitted in array constructors. The code below requires this option to expand the array at compile time.

program test
implicit none
integer j
integer, parameter :: n = 100000
integer, parameter :: i(n) = (/ (2*j, j = 1, n) /)
print '(10(I0,1X))', i
end program test

Caution: This option can lead to long compile times and excessively large object files.

The default value for n is 65535.

-fmax-stack-var-size=n

This option specifies the size in bytes of the largest array that will be put on the stack; if the size is exceeded static memory is used (except in procedures marked as RECURSIVE). Use the option -frecursive to allow for recursive procedures which do not have a RECURSIVE attribute or for parallel programs. Use -fno-automatic to never use the stack.

This option currently only affects local arrays declared with constant bounds, and may not apply to all character variables. Future versions of GNU Fortran may improve this behavior.

The default value for n is 65536.

-fstack-arrays

Adding this option will make the Fortran compiler put all arrays of unknown size and array temporaries onto stack memory. If your program uses very large local arrays it is possible that you will have to extend your runtime limits for stack memory on some operating systems. This flag is enabled by default at optimization level -Ofast unless -fmax-stack-var-size is specified.

-fpack-derived

This option tells GNU Fortran to pack derived type members as closely as possible. Code compiled with this option is likely to be incompatible with code compiled without this option, and may execute slower.

-frepack-arrays

In some circumstances GNU Fortran may pass assumed shape array sections via a descriptor describing a noncontiguous area of memory. This option adds code to the function prologue to repack the data into a contiguous block at runtime.

This should result in faster accesses to the array. However it can introduce significant overhead to the function call, especially when the passed data is noncontiguous.

-fshort-enums

This option is provided for interoperability with C code that was compiled with the -fshort-enums option. It will make GNU Fortran choose the smallest INTEGER kind a given enumerator set will fit in, and give all its enumerators this kind.

-finline-arg-packing

When passing an assumed-shape argument of a procedure as actual argument to an assumed-size or explicit size or as argument to a procedure that does not have an explicit interface, the argument may have to be packed, that is put into contiguous memory. An example is the call to foo in

  subroutine foo(a)
     real, dimension(*) :: a
  end subroutine foo
  subroutine bar(b)
     real, dimension(:) :: b
     call foo(b)
  end subroutine bar

When -finline-arg-packing is in effect, this packing will be performed by inline code. This allows for more optimization while increasing code size.

-finline-arg-packing is implied by any of the -O options except when optimizing for size via -Os. If the code contains a very large number of argument that have to be packed, code size and also compilation time may become excessive. If that is the case, it may be better to disable this option. Instances of packing can be found by using by using -Warray-temporaries.

-fexternal-blas

This option will make gfortran generate calls to BLAS functions for some matrix operations like MATMUL, instead of using our own algorithms, if the size of the matrices involved is larger than a given limit (see -fblas-matmul-limit). This may be profitable if an optimized vendor BLAS library is available. The BLAS library will have to be specified at link time.

-fblas-matmul-limit=n

Only significant when -fexternal-blas is in effect. Matrix multiplication of matrices with size larger than (or equal to) n will be performed by calls to BLAS functions, while others will be handled by gfortran internal algorithms. If the matrices involved are not square, the size comparison is performed using the geometric mean of the dimensions of the argument and result matrices.

The default value for n is 30.

-finline-matmul-limit=n

When front-end optimization is active, some calls to the MATMUL intrinsic function will be inlined. This may result in code size increase if the size of the matrix cannot be determined at compile time, as code for both cases is generated. Setting -finline-matmul-limit=0 will disable inlining in all cases. Setting this option with a value of n will produce inline code for matrices with size up to n. If the matrices involved are not square, the size comparison is performed using the geometric mean of the dimensions of the argument and result matrices.

The default value for n is 30. The -fblas-matmul-limit can be used to change this value.

-frecursive

Allow indirect recursion by forcing all local arrays to be allocated on the stack. This flag cannot be used together with -fmax-stack-var-size= or -fno-automatic.

-finit-local-zero
-finit-derived
-finit-integer=n
-finit-real=<zero|inf|-inf|nan|snan>
-finit-logical=<true|false>
-finit-character=n

The -finit-local-zero option instructs the compiler to initialize local INTEGER, REAL, and COMPLEX variables to zero, LOGICAL variables to false, and CHARACTER variables to a string of null bytes. Finer-grained initialization options are provided by the -finit-integer=n, -finit-real=<zero|inf|-inf|nan|snan> (which also initializes the real and imaginary parts of local COMPLEX variables), -finit-logical=<true|false>, and -finit-character=n (where n is an ASCII character value) options.

With -finit-derived, components of derived type variables will be initialized according to these flags. Components whose type is not covered by an explicit -finit-* flag will be treated as described above with -finit-local-zero.

These options do not initialize

  • objects with the POINTER attribute
  • allocatable arrays
  • variables that appear in an EQUIVALENCE statement.

(These limitations may be removed in future releases).

Note that the -finit-real=nan option initializes REAL and COMPLEX variables with a quiet NaN. For a signalling NaN use -finit-real=snan; note, however, that compile-time optimizations may convert them into quiet NaN and that trapping needs to be enabled (e.g. via -ffpe-trap).

The -finit-integer option will parse the value into an integer of type INTEGER(kind=C_LONG) on the host. Said value is then assigned to the integer variables in the Fortran code, which might result in wraparound if the value is too large for the kind.

Finally, note that enabling any of the -finit-* options will silence warnings that would have been emitted by -Wuninitialized for the affected local variables.

-falign-commons

By default, gfortran enforces proper alignment of all variables in a COMMON block by padding them as needed. On certain platforms this is mandatory, on others it increases performance. If a COMMON block is not declared with consistent data types everywhere, this padding can cause trouble, and -fno-align-commons can be used to disable automatic alignment. The same form of this option should be used for all files that share a COMMON block. To avoid potential alignment issues in COMMON blocks, it is recommended to order objects from largest to smallest.

-fno-protect-parens

By default the parentheses in expression are honored for all optimization levels such that the compiler does not do any re-association. Using -fno-protect-parens allows the compiler to reorder REAL and COMPLEX expressions to produce faster code. Note that for the re-association optimization -fno-signed-zeros and -fno-trapping-math need to be in effect. The parentheses protection is enabled by default, unless -Ofast is given.

-frealloc-lhs

An allocatable left-hand side of an intrinsic assignment is automatically (re)allocated if it is either unallocated or has a different shape. The option is enabled by default except when -std=f95 is given. See also -Wrealloc-lhs.

-faggressive-function-elimination

Functions with identical argument lists are eliminated within statements, regardless of whether these functions are marked PURE or not. For example, in

  a = f(b,c) + f(b,c)

there will only be a single call to f. This option only works if -ffrontend-optimize is in effect.

-ffrontend-optimize

This option performs front-end optimization, based on manipulating parts the Fortran parse tree. Enabled by default by any -O option except -O0 and -Og. Optimizations enabled by this option include:

  • inlining calls to MATMUL,
  • elimination of identical function calls within expressions,
  • removing unnecessary calls to TRIM in comparisons and assignments,
  • replacing TRIM(a) with a(1:LEN_TRIM(a)) and
  • short-circuiting of logical operators (.AND. and .OR.).

It can be deselected by specifying -fno-frontend-optimize.

-ffrontend-loop-interchange

Attempt to interchange loops in the Fortran front end where profitable. Enabled by default by any -O option. At the moment, this option only affects FORALL and DO CONCURRENT statements with several forall triplets.

See Options for Code Generation Conventions in Using the GNU Compiler Collection (GCC), for information on more options offered by the GBE shared by gfortran, gcc, and other GNU compilers.


2.10 Options for interoperability with other languages

-fc-prototypes

This option will generate C prototypes from BIND(C) variable declarations, types and procedure interfaces and writes them to standard output. ENUM is not yet supported.

The generated prototypes may need inclusion of an appropriate header, such as <stdint.h> or <stdlib.h>. For types which are not specified using the appropriate kind from the iso_c_binding module, a warning is added as a comment to the code.

For function pointers, a pointer to a function returning int without an explicit argument list is generated.

Example of use:

$ gfortran -fc-prototypes -fsyntax-only foo.f90 > foo.h

where the C code intended for interoperating with the Fortran code then uses #include "foo.h".

-fc-prototypes-external

This option will generate C prototypes from external functions and subroutines and write them to standard output. This may be useful for making sure that C bindings to Fortran code are correct. This option does not generate prototypes for BIND(C) procedures, use -fc-prototypes for that.

The generated prototypes may need inclusion of an appropriate header, such as as <stdint.h> or <stdlib.h>.

This is primarily meant for legacy code to ensure that existing C bindings match what gfortran emits. The generated C prototypes should be correct for the current version of the compiler, but may not match what other compilers or earlier versions of gfortran need. For new developments, use of the BIND(C) features is recommended.

Example of use:

$ gfortran -fc-prototypes-external -fsyntax-only foo.f > foo.h

where the C code intended for interoperating with the Fortran code then uses #include "foo.h".


2.11 Environment variables affecting gfortran

The gfortran compiler currently does not make use of any environment variables to control its operation above and beyond those that affect the operation of gcc.

See Environment Variables Affecting GCC in Using the GNU Compiler Collection (GCC), for information on environment variables.

See Runtime: Influencing runtime behavior with environment variables, for environment variables that affect the run-time behavior of programs compiled with GNU Fortran.


3 Runtime: Influencing runtime behavior with environment variables

The behavior of the gfortran can be influenced by environment variables.

Malformed environment variables are silently ignored.


3.1 TMPDIR—Directory for scratch files

When opening a file with STATUS='SCRATCH', GNU Fortran tries to create the file in one of the potential directories by testing each directory in the order below.

  1. The environment variable TMPDIR, if it exists.
  2. On the MinGW target, the directory returned by the GetTempPath function. Alternatively, on the Cygwin target, the TMP and TEMP environment variables, if they exist, in that order.
  3. The P_tmpdir macro if it is defined, otherwise the directory /tmp.

3.2 GFORTRAN_STDIN_UNIT—Unit number for standard input

This environment variable can be used to select the unit number preconnected to standard input. This must be a positive integer. The default value is 5.


3.3 GFORTRAN_STDOUT_UNIT—Unit number for standard output

This environment variable can be used to select the unit number preconnected to standard output. This must be a positive integer. The default value is 6.


3.4 GFORTRAN_STDERR_UNIT—Unit number for standard error

This environment variable can be used to select the unit number preconnected to standard error. This must be a positive integer. The default value is 0.


3.5 GFORTRAN_UNBUFFERED_ALL—Do not buffer I/O on all units

This environment variable controls whether all I/O is unbuffered. If the first letter is ‘y’, ‘Y’ or ‘1’, all I/O is unbuffered. This will slow down small sequential reads and writes. If the first letter is ‘n’, ‘N’ or ‘0’, I/O is buffered. This is the default.


3.6 GFORTRAN_UNBUFFERED_PRECONNECTED—Do not buffer I/O on preconnected units

The environment variable named GFORTRAN_UNBUFFERED_PRECONNECTED controls whether I/O on a preconnected unit (i.e. STDOUT or STDERR) is unbuffered. If the first letter is ‘y’, ‘Y’ or ‘1’, I/O is unbuffered. This will slow down small sequential reads and writes. If the first letter is ‘n’, ‘N’ or ‘0’, I/O is buffered. This is the default.


3.7 GFORTRAN_SHOW_LOCUS—Show location for runtime errors

If the first letter is ‘y’, ‘Y’ or ‘1’, filename and line numbers for runtime errors are printed. If the first letter is ‘n’, ‘N’ or ‘0’, do not print filename and line numbers for runtime errors. The default is to print the location.


3.8 GFORTRAN_OPTIONAL_PLUS—Print leading + where permitted

If the first letter is ‘y’, ‘Y’ or ‘1’, a plus sign is printed where permitted by the Fortran standard. If the first letter is ‘n’, ‘N’ or ‘0’, a plus sign is not printed in most cases. Default is not to print plus signs.


3.9 GFORTRAN_LIST_SEPARATOR—Separator for list output

This environment variable specifies the separator when writing list-directed output. It may contain any number of spaces and at most one comma. If you specify this on the command line, be sure to quote spaces, as in

$ GFORTRAN_LIST_SEPARATOR='  ,  ' ./a.out

when a.out is the compiled Fortran program that you want to run. Default is a single space.


3.10 GFORTRAN_CONVERT_UNIT—Set endianness for unformatted I/O

By setting the GFORTRAN_CONVERT_UNIT variable, it is possible to change the representation of data for unformatted files. The syntax for the GFORTRAN_CONVERT_UNIT variable is:

GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;
mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;
exception: mode ':' unit_list | unit_list ;
unit_list: unit_spec | unit_list unit_spec ;
unit_spec: INTEGER | INTEGER '-' INTEGER ;

The variable consists of an optional default mode, followed by a list of optional exceptions, which are separated by semicolons from the preceding default and each other. Each exception consists of a format and a comma-separated list of units. Valid values for the modes are the same as for the CONVERT specifier:

  • NATIVE Use the native format. This is the default.
  • SWAP Swap between little- and big-endian.
  • LITTLE_ENDIAN Use the little-endian format for unformatted files.
  • BIG_ENDIAN Use the big-endian format for unformatted files.

A missing mode for an exception is taken to mean BIG_ENDIAN. Examples of values for GFORTRAN_CONVERT_UNIT are:

  • 'big_endian' Do all unformatted I/O in big_endian mode.
  • 'little_endian;native:10-20,25' Do all unformatted I/O in little_endian mode, except for units 10 to 20 and 25, which are in native format.
  • '10-20' Units 10 to 20 are big-endian, the rest is native.

Setting the environment variables should be done on the command line or via the export command for sh-compatible shells and via setenv for csh-compatible shells.

Example for sh:

$ gfortran foo.f90
$ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out

Example code for csh:

% gfortran foo.f90
% setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
% ./a.out

Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable.

See CONVERT specifier, for an alternative way to specify the data representation for unformatted files. See Influencing runtime behavior, for setting a default data representation for the whole program. The CONVERT specifier overrides the -fconvert compile options.

Note that the values specified via the GFORTRAN_CONVERT_UNIT environment variable will override the CONVERT specifier in the open statement. This is to give control over data formats to users who do not have the source code of their program available.


3.11 GFORTRAN_ERROR_BACKTRACE—Show backtrace on run-time errors

If the GFORTRAN_ERROR_BACKTRACE variable is set to ‘y’, ‘Y’ or ‘1’ (only the first letter is relevant) then a backtrace is printed when a serious run-time error occurs. To disable the backtracing, set the variable to ‘n’, ‘N’, ‘0’. Default is to print a backtrace unless the -fno-backtrace compile option was used.


3.12 GFORTRAN_FORMATTED_BUFFER_SIZE—Set buffer size for formatted I/O

The GFORTRAN_FORMATTED_BUFFER_SIZE environment variable specifies buffer size in bytes to be used for formatted output. The default value is 8192.


3.13 GFORTRAN_UNFORMATTED_BUFFER_SIZE—Set buffer size for unformatted I/O

The GFORTRAN_UNFORMATTED_BUFFER_SIZE environment variable specifies buffer size in bytes to be used for unformatted output. The default value is 131072.


4 Fortran standards status


4.1 Fortran 2003 status

GNU Fortran supports several Fortran 2003 features; an incomplete list can be found below. See also the wiki page about Fortran 2003.

  • Procedure pointers including procedure-pointer components with PASS attribute.
  • Procedures which are bound to a derived type (type-bound procedures) including PASS, PROCEDURE and GENERIC, and operators bound to a type.
  • Abstract interfaces and type extension with the possibility to override type-bound procedures or to have deferred binding.
  • Polymorphic entities (“CLASS”) for derived types and unlimited polymorphism (“CLASS(*)”) – including SAME_TYPE_AS, EXTENDS_TYPE_OF and SELECT TYPE for scalars and arrays and finalization.
  • Generic interface names, which have the same name as derived types, are now supported. This allows one to write constructor functions. Note that Fortran does not support static constructor functions. For static variables, only default initialization or structure-constructor initialization are available.
  • The ASSOCIATE construct.
  • Interoperability with C including enumerations,
  • In structure constructors the components with default values may be omitted.
  • Extensions to the ALLOCATE statement, allowing for a type-specification with type parameter and for allocation and initialization from a SOURCE= expression; ALLOCATE and DEALLOCATE optionally return an error message string via ERRMSG=.
  • Reallocation on assignment: If an intrinsic assignment is used, an allocatable variable on the left-hand side is automatically allocated (if unallocated) or reallocated (if the shape is different). Currently, scalar deferred character length left-hand sides are correctly handled but arrays are not yet fully implemented.
  • Deferred-length character variables and scalar deferred-length character components of derived types are supported. (Note that array-valued components are not yet implemented.)
  • Transferring of allocations via MOVE_ALLOC.
  • The PRIVATE and PUBLIC attributes may be given individually to derived-type components.
  • In pointer assignments, the lower bound may be specified and the remapping of elements is supported.
  • For pointers an INTENT may be specified which affect the association status not the value of the pointer target.
  • Intrinsics command_argument_count, get_command, get_command_argument, and get_environment_variable.
  • Support for Unicode characters (ISO 10646) and UTF-8, including the SELECTED_CHAR_KIND and NEW_LINE intrinsic functions.
  • Support for binary, octal and hexadecimal (BOZ) constants in the intrinsic functions INT, REAL, CMPLX and DBLE.
  • Support for namelist variables with allocatable and pointer attribute and nonconstant length type parameter.
  • Array constructors using square brackets. That is, [...] rather than (/.../). Type-specification for array constructors like (/ some-type :: ... /).
  • Extensions to the specification and initialization expressions, including the support for intrinsics with real and complex arguments.
  • Support for the asynchronous input/output.
  • FLUSH statement.
  • IOMSG= specifier for I/O statements.
  • Support for the declaration of enumeration constants via the ENUM and ENUMERATOR statements. Interoperability with gcc is guaranteed also for the case where the -fshort-enums command line option is given.
  • TR 15581:
    • ALLOCATABLE dummy arguments.
    • ALLOCATABLE function results
    • ALLOCATABLE components of derived types
  • The OPEN statement supports the ACCESS='STREAM' specifier, allowing I/O without any record structure.
  • Namelist input/output for internal files.
  • Minor I/O features: Rounding during formatted output, using of a decimal comma instead of a decimal point, setting whether a plus sign should appear for positive numbers. On systems where strtod honours the rounding mode, the rounding mode is also supported for input.
  • The PROTECTED statement and attribute.
  • The VALUE statement and attribute.
  • The VOLATILE statement and attribute.
  • The IMPORT statement, allowing to import host-associated derived types.
  • The intrinsic modules ISO_FORTRAN_ENVIRONMENT is supported, which contains parameters of the I/O units, storage sizes. Additionally, procedures for C interoperability are available in the ISO_C_BINDING module.
  • USE statement with INTRINSIC and NON_INTRINSIC attribute; supported intrinsic modules: ISO_FORTRAN_ENV, ISO_C_BINDING, OMP_LIB and OMP_LIB_KINDS, and OPENACC.
  • Renaming of operators in the USE statement.

4.2 Fortran 2008 status

The latest version of the Fortran standard is ISO/IEC 1539-1:2010, informally known as Fortran 2008. The official version is available from International Organization for Standardization (ISO) or its national member organizations. The the final draft (FDIS) can be downloaded free of charge from http://www.nag.co.uk/sc22wg5/links.html. Fortran is developed by the Working Group 5 of Sub-Committee 22 of the Joint Technical Committee 1 of the International Organization for Standardization and the International Electrotechnical Commission (IEC). This group is known as WG5.

The GNU Fortran compiler supports several of the new features of Fortran 2008; the wiki has some information about the current Fortran 2008 implementation status. In particular, the following is implemented.

  • The -std=f2008 option and support for the file extensions .f08 and .F08.
  • The OPEN statement now supports the NEWUNIT= option, which returns a unique file unit, thus preventing inadvertent use of the same unit in different parts of the program.
  • The g0 format descriptor and unlimited format items.
  • The mathematical intrinsics ASINH, ACOSH, ATANH, ERF, ERFC, GAMMA, LOG_GAMMA, BESSEL_J0, BESSEL_J1, BESSEL_JN, BESSEL_Y0, BESSEL_Y1, BESSEL_YN, HYPOT, NORM2, and ERFC_SCALED.
  • Using complex arguments with TAN, SINH, COSH, TANH, ASIN, ACOS, and ATAN is now possible; ATAN(Y,X) is now an alias for ATAN2(Y,X).
  • Support of the PARITY intrinsic functions.
  • The following bit intrinsics: LEADZ and TRAILZ for counting the number of leading and trailing zero bits, POPCNT and POPPAR for counting the number of one bits and returning the parity; BGE, BGT, BLE, and BLT for bitwise comparisons; DSHIFTL and DSHIFTR for combined left and right shifts, MASKL and MASKR for simple left and right justified masks, MERGE_BITS for a bitwise merge using a mask, SHIFTA, SHIFTL and SHIFTR for shift operations, and the transformational bit intrinsics IALL, IANY and IPARITY.
  • Support of the EXECUTE_COMMAND_LINE intrinsic subroutine.
  • Support for the STORAGE_SIZE intrinsic inquiry function.
  • The INT{8,16,32} and REAL{32,64,128} kind type parameters and the array-valued named constants INTEGER_KINDS, LOGICAL_KINDS, REAL_KINDS and CHARACTER_KINDS of the intrinsic module ISO_FORTRAN_ENV.
  • The module procedures C_SIZEOF of the intrinsic module ISO_C_BINDINGS and COMPILER_VERSION and COMPILER_OPTIONS of ISO_FORTRAN_ENV.
  • Coarray support for serial programs with -fcoarray=single flag and experimental support for multiple images with the -fcoarray=lib flag.
  • Submodules are supported. It should noted that MODULEs do not produce the smod file needed by the descendent SUBMODULEs unless they contain at least one MODULE PROCEDURE interface. The reason for this is that SUBMODULEs are useless without MODULE PROCEDUREs. See http://j3-fortran.org/doc/meeting/207/15-209.txt for a discussion and a draft interpretation. Adopting this interpretation has the advantage that code that does not use submodules does not generate smod files.
  • The DO CONCURRENT construct is supported.
  • The BLOCK construct is supported.
  • The STOP and the new ERROR STOP statements now support all constant expressions. Both show the signals which were signaling at termination.
  • Support for the CONTIGUOUS attribute.
  • Support for ALLOCATE with MOLD.
  • Support for the IMPURE attribute for procedures, which allows for ELEMENTAL procedures without the restrictions of PURE.
  • Null pointers (including NULL()) and not-allocated variables can be used as actual argument to optional non-pointer, non-allocatable dummy arguments, denoting an absent argument.
  • Non-pointer variables with TARGET attribute can be used as actual argument to POINTER dummies with INTENT(IN).
  • Pointers including procedure pointers and those in a derived type (pointer components) can now be initialized by a target instead of only by NULL.
  • The EXIT statement (with construct-name) can be now be used to leave not only the DO but also the ASSOCIATE, BLOCK, IF, SELECT CASE and SELECT TYPE constructs.
  • Internal procedures can now be used as actual argument.
  • Minor features: obsolesce diagnostics for ENTRY with -std=f2008; a line may start with a semicolon; for internal and module procedures END can be used instead of END SUBROUTINE and END FUNCTION; SELECTED_REAL_KIND now also takes a RADIX argument; intrinsic types are supported for TYPE(intrinsic-type-spec); multiple type-bound procedures can be declared in a single PROCEDURE statement; implied-shape arrays are supported for named constants (PARAMETER).

4.3 Status of Fortran 2018 support

  • ERROR STOP in a PURE procedure An ERROR STOP statement is permitted in a PURE procedure.
  • IMPLICIT NONE with a spec-list Support the IMPLICIT NONE statement with an implicit-none-spec-list.
  • Behavior of INQUIRE with the RECL= specifier

    The behavior of the INQUIRE statement with the RECL= specifier now conforms to Fortran 2018.

4.3.1 TS 29113 Status (Further Interoperability with C)

GNU Fortran supports some of the new features of the Technical Specification (TS) 29113 on Further Interoperability of Fortran with C. The wiki has some information about the current TS 29113 implementation status. In particular, the following is implemented.

See also Further Interoperability of Fortran with C.

  • The OPTIONAL attribute is allowed for dummy arguments of BIND(C) procedures.
  • The RANK intrinsic is supported.
  • GNU Fortran’s implementation for variables with ASYNCHRONOUS attribute is compatible with TS 29113.
  • Assumed types (TYPE(*)).
  • Assumed-rank (DIMENSION(..)).
  • ISO_Fortran_binding (now in Fortran 2018 18.4) is implemented such that conversion of the array descriptor for assumed type or assumed rank arrays is done in the library. The include file ISO_Fortran_binding.h is can be found in ~prefix/lib/gcc/$target/$version.

4.3.2 TS 18508 Status (Additional Parallel Features)

GNU Fortran supports the following new features of the Technical Specification 18508 on Additional Parallel Features in Fortran:

  • The new atomic ADD, CAS, FETCH and ADD/OR/XOR, OR and XOR intrinsics.
  • The CO_MIN and CO_MAX and SUM reduction intrinsics. And the CO_BROADCAST and CO_REDUCE intrinsic, except that those do not support polymorphic types or types with allocatable, pointer or polymorphic components.
  • Events (EVENT POST, EVENT WAIT, EVENT_QUERY)
  • Failed images (FAIL IMAGE, IMAGE_STATUS, FAILED_IMAGES, STOPPED_IMAGES)

5 Compiler Characteristics

This chapter describes certain characteristics of the GNU Fortran compiler, that are not specified by the Fortran standard, but which might in some way or another become visible to the programmer.


5.1 KIND Type Parameters

The KIND type parameters supported by GNU Fortran for the primitive data types are:

INTEGER

1, 2, 4, 8*, 16*, default: 4**

LOGICAL

1, 2, 4, 8*, 16*, default: 4**

REAL

4, 8, 10*, 16*, default: 4***

COMPLEX

4, 8, 10*, 16*, default: 4***

DOUBLE PRECISION

4, 8, 10*, 16*, default: 8***

CHARACTER

1, 4, default: 1

* not available on all systems
** unless -fdefault-integer-8 is used
*** unless -fdefault-real-8 is used (see Options controlling Fortran dialect)

The KIND value matches the storage size in bytes, except for COMPLEX where the storage size is twice as much (or both real and imaginary part are a real value of the given size). It is recommended to use the SELECTED_CHAR_KIND — Choose character kind, SELECTED_INT_KIND — Choose integer kind and SELECTED_REAL_KIND — Choose real kind intrinsics or the INT8, INT16, INT32, INT64, REAL32, REAL64, and REAL128 parameters of the ISO_FORTRAN_ENV module instead of the concrete values. The available kind parameters can be found in the constant arrays CHARACTER_KINDS, INTEGER_KINDS, LOGICAL_KINDS and REAL_KINDS in the ISO_FORTRAN_ENV module. For C interoperability, the kind parameters of the ISO_C_BINDING module should be used.


5.2 Internal representation of LOGICAL variables

The Fortran standard does not specify how variables of LOGICAL type are represented, beyond requiring that LOGICAL variables of default kind have the same storage size as default INTEGER and REAL variables. The GNU Fortran internal representation is as follows.

A LOGICAL(KIND=N) variable is represented as an INTEGER(KIND=N) variable, however, with only two permissible values: 1 for .TRUE. and 0 for .FALSE.. Any other integer value results in undefined behavior.

See also Argument passing conventions and Interoperability with C.


5.3 Evaluation of logical expressions

The Fortran standard does not require the compiler to evaluate all parts of an expression, if they do not contribute to the final result. For logical expressions with .AND. or .OR. operators, in particular, GNU Fortran will optimize out function calls (even to impure functions) if the result of the expression can be established without them. However, since not all compilers do that, and such an optimization can potentially modify the program flow and subsequent results, GNU Fortran throws warnings for such situations with the -Wfunction-elimination flag.


5.4 MAX and MIN intrinsics with REAL NaN arguments

The Fortran standard does not specify what the result of the MAX and MIN intrinsics are if one of the arguments is a NaN. Accordingly, the GNU Fortran compiler does not specify that either, as this allows for faster and more compact code to be generated. If the programmer wishes to take some specific action in case one of the arguments is a NaN, it is necessary to explicitly test the arguments before calling MAX or MIN, e.g. with the IEEE_IS_NAN function from the intrinsic module IEEE_ARITHMETIC.


5.5 Thread-safety of the runtime library

GNU Fortran can be used in programs with multiple threads, e.g. by using OpenMP, by calling OS thread handling functions via the ISO_C_BINDING facility, or by GNU Fortran compiled library code being called from a multi-threaded program.

The GNU Fortran runtime library, (libgfortran), supports being called concurrently from multiple threads with the following exceptions.

During library initialization, the C getenv function is used, which need not be thread-safe. Similarly, the getenv function is used to implement the GET_ENVIRONMENT_VARIABLE and GETENV intrinsics. It is the responsibility of the user to ensure that the environment is not being updated concurrently when any of these actions are taking place.

The EXECUTE_COMMAND_LINE and SYSTEM intrinsics are implemented with the system function, which need not be thread-safe. It is the responsibility of the user to ensure that system is not called concurrently.

For platforms not supporting thread-safe POSIX functions, further functionality might not be thread-safe. For details, please consult the documentation for your operating system.

The GNU Fortran runtime library uses various C library functions that depend on the locale, such as strtod and snprintf. In order to work correctly in locale-aware programs that set the locale using setlocale, the locale is reset to the default “C” locale while executing a formatted READ or WRITE statement. On targets supporting the POSIX 2008 per-thread locale functions (e.g. newlocale, uselocale, freelocale), these are used and thus the global locale set using setlocale or the per-thread locales in other threads are not affected. However, on targets lacking this functionality, the global LC_NUMERIC locale is set to “C” during the formatted I/O. Thus, on such targets it’s not safe to call setlocale concurrently from another thread while a Fortran formatted I/O operation is in progress. Also, other threads doing something dependent on the LC_NUMERIC locale might not work correctly if a formatted I/O operation is in progress in another thread.


5.6 Data consistency and durability

This section contains a brief overview of data and metadata consistency and durability issues when doing I/O.

With respect to durability, GNU Fortran makes no effort to ensure that data is committed to stable storage. If this is required, the GNU Fortran programmer can use the intrinsic FNUM to retrieve the low level file descriptor corresponding to an open Fortran unit. Then, using e.g. the ISO_C_BINDING feature, one can call the underlying system call to flush dirty data to stable storage, such as fsync on POSIX, _commit on MingW, or fcntl(fd, F_FULLSYNC, 0) on Mac OS X. The following example shows how to call fsync:

  ! Declare the interface for POSIX fsync function
  interface
    function fsync (fd) bind(c,name="fsync")
    use iso_c_binding, only: c_int
      integer(c_int), value :: fd
      integer(c_int) :: fsync
    end function fsync
  end interface

  ! Variable declaration
  integer :: ret

  ! Opening unit 10
  open (10,file="foo")

  ! ...
  ! Perform I/O on unit 10
  ! ...

  ! Flush and sync
  flush(10)
  ret = fsync(fnum(10))

  ! Handle possible error
  if (ret /= 0) stop "Error calling FSYNC"

With respect to consistency, for regular files GNU Fortran uses buffered I/O in order to improve performance. This buffer is flushed automatically when full and in some other situations, e.g. when closing a unit. It can also be explicitly flushed with the FLUSH statement. Also, the buffering can be turned off with the GFORTRAN_UNBUFFERED_ALL and GFORTRAN_UNBUFFERED_PRECONNECTED environment variables. Special files, such as terminals and pipes, are always unbuffered. Sometimes, however, further things may need to be done in order to allow other processes to see data that GNU Fortran has written, as follows.

The Windows platform supports a relaxed metadata consistency model, where file metadata is written to the directory lazily. This means that, for instance, the dir command can show a stale size for a file. One can force a directory metadata update by closing the unit, or by calling _commit on the file descriptor. Note, though, that _commit will force all dirty data to stable storage, which is often a very slow operation.

The Network File System (NFS) implements a relaxed consistency model called open-to-close consistency. Closing a file forces dirty data and metadata to be flushed to the server, and opening a file forces the client to contact the server in order to revalidate cached data. fsync will also force a flush of dirty data and metadata to the server. Similar to open and close, acquiring and releasing fcntl file locks, if the server supports them, will also force cache validation and flushing dirty data and metadata.


5.7 Files opened without an explicit ACTION= specifier

The Fortran standard says that if an OPEN statement is executed without an explicit ACTION= specifier, the default value is processor dependent. GNU Fortran behaves as follows:

  1. Attempt to open the file with ACTION='READWRITE'
  2. If that fails, try to open with ACTION='READ'
  3. If that fails, try to open with ACTION='WRITE'
  4. If that fails, generate an error

5.9 File format of unformatted sequential files

Unformatted sequential files are stored as logical records using record markers. Each logical record consists of one of more subrecords.

Each subrecord consists of a leading record marker, the data written by the user program, and a trailing record marker. The record markers are four-byte integers by default, and eight-byte integers if the -fmax-subrecord-length=8 option (which exists for backwards compability only) is in effect.

The representation of the record markers is that of unformatted files given with the -fconvert option, the CONVERT specifier in an open statement or the GFORTRAN_CONVERT_UNIT—Set endianness for unformatted I/O environment variable.

The maximum number of bytes of user data in a subrecord is 2147483639 (2 GiB - 9) for a four-byte record marker. This limit can be lowered with the -fmax-subrecord-length option, altough this is rarely useful. If the length of a logical record exceeds this limit, the data is distributed among several subrecords.

The absolute of the number stored in the record markers is the number of bytes of user data in the corresponding subrecord. If the leading record marker of a subrecord contains a negative number, another subrecord follows the current one. If the trailing record marker contains a negative number, then there is a preceding subrecord.

In the most simple case, with only one subrecord per logical record, both record markers contain the number of bytes of user data in the record.

The format for unformatted sequential data can be duplicated using unformatted stream, as shown in the example program for an unformatted record containing a single subrecord:

program main
  use iso_fortran_env, only: int32
  implicit none
  integer(int32) :: i
  real, dimension(10) :: a, b
  call random_number(a)
  open (10,file='test.dat',form='unformatted',access='stream')
  inquire (iolength=i) a
  write (10) i, a, i
  close (10)
  open (10,file='test.dat',form='unformatted')
  read (10) b
  if (all (a == b)) print *,'success!'
end program main

5.10 Asynchronous I/O

Asynchronous I/O is supported if the program is linked against the POSIX thread library. If that is not the case, all I/O is performed as synchronous. On systems which do not support pthread condition variables, such as AIX, I/O is also performed as synchronous.

On some systems, such as Darwin or Solaris, the POSIX thread library is always linked in, so asynchronous I/O is always performed. On other sytems, such as Linux, it is necessary to specify -pthread, -lpthread or -fopenmp during the linking step.


6 Extensions

The two sections below detail the extensions to standard Fortran that are implemented in GNU Fortran, as well as some of the popular or historically important extensions that are not (or not yet) implemented. For the latter case, we explain the alternatives available to GNU Fortran users, including replacement by standard-conforming code or GNU extensions.


6.1 Extensions implemented in GNU Fortran

GNU Fortran implements a number of extensions over standard Fortran. This chapter contains information on their syntax and meaning. There are currently two categories of GNU Fortran extensions, those that provide functionality beyond that provided by any standard, and those that are supported by GNU Fortran purely for backward compatibility with legacy compilers. By default, -std=gnu allows the compiler to accept both types of extensions, but to warn about the use of the latter. Specifying either -std=f95, -std=f2003, -std=f2008, or -std=f2018 disables both types of extensions, and -std=legacy allows both without warning. The special compile flag -fdec enables additional compatibility extensions along with those enabled by -std=legacy.


6.1.1 Old-style kind specifications

GNU Fortran allows old-style kind specifications in declarations. These look like:

      TYPESPEC*size x,y,z

where TYPESPEC is a basic type (INTEGER, REAL, etc.), and where size is a byte count corresponding to the storage size of a valid kind for that type. (For COMPLEX variables, size is the total size of the real and imaginary parts.) The statement then declares x, y and z to be of type TYPESPEC with the appropriate kind. This is equivalent to the standard-conforming declaration

      TYPESPEC(k) x,y,z

where k is the kind parameter suitable for the intended precision. As kind parameters are implementation-dependent, use the KIND, SELECTED_INT_KIND and SELECTED_REAL_KIND intrinsics to retrieve the correct value, for instance REAL*8 x can be replaced by:

INTEGER, PARAMETER :: dbl = KIND(1.0d0)
REAL(KIND=dbl) :: x

6.1.2 Old-style variable initialization

GNU Fortran allows old-style initialization of variables of the form:

      INTEGER i/1/,j/2/
      REAL x(2,2) /3*0.,1./

The syntax for the initializers is as for the DATA statement, but unlike in a DATA statement, an initializer only applies to the variable immediately preceding the initialization. In other words, something like INTEGER I,J/2,3/ is not valid. This style of initialization is only allowed in declarations without double colons (::); the double colons were introduced in Fortran 90, which also introduced a standard syntax for initializing variables in type declarations.

Examples of standard-conforming code equivalent to the above example are:

! Fortran 90
      INTEGER :: i = 1, j = 2
      REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
! Fortran 77
      INTEGER i, j
      REAL x(2,2)
      DATA i/1/, j/2/, x/3*0.,1./

Note that variables which are explicitly initialized in declarations or in DATA statements automatically acquire the SAVE attribute.


6.1.3 Extensions to namelist

GNU Fortran fully supports the Fortran 95 standard for namelist I/O including array qualifiers, substrings and fully qualified derived types. The output from a namelist write is compatible with namelist read. The output has all names in upper case and indentation to column 1 after the namelist name. Two extensions are permitted:

Old-style use of ‘$’ instead of ‘&

$MYNML
 X(:)%Y(2) = 1.0 2.0 3.0
 CH(1:4) = "abcd"
$END

It should be noted that the default terminator is ‘/’ rather than ‘&END’.

Querying of the namelist when inputting from stdin. After at least one space, entering ‘?’ sends to stdout the namelist name and the names of the variables in the namelist:

 ?

&mynml
 x
 x%y
 ch
&end

Entering ‘=?’ outputs the namelist to stdout, as if WRITE(*,NML = mynml) had been called:

=?

&MYNML
 X(1)%Y=  0.000000    ,  1.000000    ,  0.000000    ,
 X(2)%Y=  0.000000    ,  2.000000    ,  0.000000    ,
 X(3)%Y=  0.000000    ,  3.000000    ,  0.000000    ,
 CH=abcd,  /

To aid this dialog, when input is from stdin, errors send their messages to stderr and execution continues, even if IOSTAT is set.

PRINT namelist is permitted. This causes an error if -std=f95 is used.

PROGRAM test_print
  REAL, dimension (4)  ::  x = (/1.0, 2.0, 3.0, 4.0/)
  NAMELIST /mynml/ x
  PRINT mynml
END PROGRAM test_print

Expanded namelist reads are permitted. This causes an error if -std=f95 is used. In the following example, the first element of the array will be given the value 0.00 and the two succeeding elements will be given the values 1.00 and 2.00.

&MYNML
  X(1,1) = 0.00 , 1.00 , 2.00
/

When writing a namelist, if no DELIM= is specified, by default a double quote is used to delimit character strings. If -std=F95, F2003, or F2008, etc, the delim status is set to ’none’. Defaulting to quotes ensures that namelists with character strings can be subsequently read back in accurately.


6.1.4 X format descriptor without count field

To support legacy codes, GNU Fortran permits the count field of the X edit descriptor in FORMAT statements to be omitted. When omitted, the count is implicitly assumed to be one.

       PRINT 10, 2, 3
10     FORMAT (I1, X, I1)

6.1.5 Commas in FORMAT specifications

To support legacy codes, GNU Fortran allows the comma separator to be omitted immediately before and after character string edit descriptors in FORMAT statements. A comma with no following format decriptor is permited if the -fdec-blank-format-item is given on the command line. This is considered non-conforming code and is discouraged.

       PRINT 10, 2, 3
10     FORMAT ('FOO='I1' BAR='I2)
       print 20, 5, 6
20     FORMAT (I3, I3,)

6.1.6 Missing period in FORMAT specifications

To support legacy codes, GNU Fortran allows missing periods in format specifications if and only if -std=legacy is given on the command line. This is considered non-conforming code and is discouraged.

       REAL :: value
       READ(*,10) value
10     FORMAT ('F4')

6.1.7 Default widths for F, G and I format descriptors

To support legacy codes, GNU Fortran allows width to be omitted from format specifications if and only if -fdec-format-defaults is given on the command line. Default widths will be used. This is considered non-conforming code and is discouraged.

       REAL :: value1
       INTEGER :: value2
       WRITE(*,10) value1, value1, value2
10     FORMAT ('F, G, I')

6.1.8 I/O item lists

To support legacy codes, GNU Fortran allows the input item list of the READ statement, and the output item lists of the WRITE and PRINT statements, to start with a comma.


6.1.9 Q exponent-letter

GNU Fortran accepts real literal constants with an exponent-letter of Q, for example, 1.23Q45. The constant is interpreted as a REAL(16) entity on targets that support this type. If the target does not support REAL(16) but has a REAL(10) type, then the real-literal-constant will be interpreted as a REAL(10) entity. In the absence of REAL(16) and REAL(10), an error will occur.


6.1.10 BOZ literal constants

Besides decimal constants, Fortran also supports binary (b), octal (o) and hexadecimal (z) integer constants. The syntax is: ‘prefix quote digits quote’, were the prefix is either b, o or z, quote is either ' or " and the digits are 0 or 1 for binary, between 0 and 7 for octal, and between 0 and F for hexadecimal. (Example: b'01011101'.)

Up to Fortran 95, BOZ literal constants were only allowed to initialize integer variables in DATA statements. Since Fortran 2003 BOZ literal constants are also allowed as actual arguments to the REAL, DBLE, INT and CMPLX intrinsic functions. The BOZ literal constant is simply a string of bits, which is padded or truncated as needed, during conversion to a numeric type. The Fortran standard states that the treatment of the sign bit is processor dependent. Gfortran interprets the sign bit as a user would expect.

As a deprecated extension, GNU Fortran allows hexadecimal BOZ literal constants to be specified using the X prefix. That the BOZ literal constant can also be specified by adding a suffix to the string, for example, Z'ABC' and 'ABC'X are equivalent. Additionally, as extension, BOZ literals are permitted in some contexts outside of DATA and the intrinsic functions listed in the Fortran standard. Use -fallow-invalid-boz to enable the extension.


6.1.11 Real array indices

As an extension, GNU Fortran allows the use of REAL expressions or variables as array indices.


6.1.12 Unary operators

As an extension, GNU Fortran allows unary plus and unary minus operators to appear as the second operand of binary arithmetic operators without the need for parenthesis.

       X = Y * -Z

6.1.13 Implicitly convert LOGICAL and INTEGER values

As an extension for backwards compatibility with other compilers, GNU Fortran allows the implicit conversion of LOGICAL values to INTEGER values and vice versa. When converting from a LOGICAL to an INTEGER, .FALSE. is interpreted as zero, and .TRUE. is interpreted as one. When converting from INTEGER to LOGICAL, the value zero is interpreted as .FALSE. and any nonzero value is interpreted as .TRUE..

        LOGICAL :: l
        l = 1
        INTEGER :: i
        i = .TRUE.

However, there is no implicit conversion of INTEGER values in if-statements, nor of LOGICAL or INTEGER values in I/O operations.


6.1.14 Hollerith constants support

GNU Fortran supports Hollerith constants in assignments, DATA statements, function and subroutine arguments. A Hollerith constant is written as a string of characters preceded by an integer constant indicating the character count, and the letter H or h, and stored in bytewise fashion in a numeric (INTEGER, REAL, or COMPLEX), LOGICAL or CHARACTER variable. The constant will be padded with spaces or truncated to fit the size of the variable in which it is stored.

Examples of valid uses of Hollerith constants:

      complex*16 x(2)
      data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
      x(1) = 16HABCDEFGHIJKLMNOP
      call foo (4h abc)

Examples of Hollerith constants:

      integer*4 a
      a = 0H         ! Invalid, at least one character is needed.
      a = 4HAB12     ! Valid
      a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
      a = 3Hxyz      ! Valid, but the Hollerith constant will be padded.

In general, Hollerith constants were used to provide a rudimentary facility for handling character strings in early Fortran compilers, prior to the introduction of CHARACTER variables in Fortran 77; in those cases, the standard-compliant equivalent is to convert the program to use proper character strings. On occasion, there may be a case where the intent is specifically to initialize a numeric variable with a given byte sequence. In these cases, the same result can be obtained by using the TRANSFER statement, as in this example.

      integer(kind=4) :: a
      a = transfer ("abcd", a)     ! equivalent to: a = 4Habcd

The use of the -fdec option extends support of Hollerith constants to comparisons:

      integer*4 a
      a = 4hABCD
      if (a .ne. 4habcd) then
        write(*,*) "no match"
      end if

Supported types are numeric (INTEGER, REAL, or COMPLEX), and CHARACTER.


6.1.15 Character conversion

Allowing character literals to be used in a similar way to Hollerith constants is a non-standard extension. This feature is enabled using -fdec-char-conversions and only applies to character literals of kind=1.

Character literals can be used in DATA statements and assignments with numeric (INTEGER, REAL, or COMPLEX) or LOGICAL variables. Like Hollerith constants they are copied byte-wise fashion. The constant will be padded with spaces or truncated to fit the size of the variable in which it is stored.

Examples:

      integer*4 x
      data x / 'abcd' /

      x = 'A'       ! Will be padded.
      x = 'ab1234'  ! Will be truncated.

6.1.16 Cray pointers

Cray pointers are part of a non-standard extension that provides a C-like pointer in Fortran. This is accomplished through a pair of variables: an integer "pointer" that holds a memory address, and a "pointee" that is used to dereference the pointer.

Pointer/pointee pairs are declared in statements of the form:

        pointer ( <pointer> , <pointee> )

or,

        pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...

The pointer is an integer that is intended to hold a memory address. The pointee may be an array or scalar. If an assumed-size array is permitted within the scoping unit, a pointee can be an assumed-size array. That is, the last dimension may be left unspecified by using a * in place of a value. A pointee cannot be an assumed shape array. No space is allocated for the pointee.

The pointee may have its type declared before or after the pointer statement, and its array specification (if any) may be declared before, during, or after the pointer statement. The pointer may be declared as an integer prior to the pointer statement. However, some machines have default integer sizes that are different than the size of a pointer, and so the following code is not portable:

        integer ipt
        pointer (ipt, iarr)

If a pointer is declared with a kind that is too small, the compiler will issue a warning; the resulting binary will probably not work correctly, because the memory addresses stored in the pointers may be truncated. It is safer to omit the first line of the above example; if explicit declaration of ipt’s type is omitted, then the compiler will ensure that ipt is an integer variable large enough to hold a pointer.

Pointer arithmetic is valid with Cray pointers, but it is not the same as C pointer arithmetic. Cray pointers are just ordinary integers, so the user is responsible for determining how many bytes to add to a pointer in order to increment it. Consider the following example:

        real target(10)
        real pointee(10)
        pointer (ipt, pointee)
        ipt = loc (target)
        ipt = ipt + 1

The last statement does not set ipt to the address of target(1), as it would in C pointer arithmetic. Adding 1 to ipt just adds one byte to the address stored in ipt.

Any expression involving the pointee will be translated to use the value stored in the pointer as the base address.

To get the address of elements, this extension provides an intrinsic function LOC(). The LOC() function is equivalent to the & operator in C, except the address is cast to an integer type:

        real ar(10)
        pointer(ipt, arpte(10))
        real arpte
        ipt = loc(ar)  ! Makes arpte is an alias for ar
        arpte(1) = 1.0 ! Sets ar(1) to 1.0

The pointer can also be set by a call to the MALLOC intrinsic (see MALLOC — Allocate dynamic memory).

Cray pointees often are used to alias an existing variable. For example:

        integer target(10)
        integer iarr(10)
        pointer (ipt, iarr)
        ipt = loc(target)

As long as ipt remains unchanged, iarr is now an alias for target. The optimizer, however, will not detect this aliasing, so it is unsafe to use iarr and target simultaneously. Using a pointee in any way that violates the Fortran aliasing rules or assumptions is illegal. It is the user’s responsibility to avoid doing this; the compiler works under the assumption that no such aliasing occurs.

Cray pointers will work correctly when there is no aliasing (i.e., when they are used to access a dynamically allocated block of memory), and also in any routine where a pointee is used, but any variable with which it shares storage is not used. Code that violates these rules may not run as the user intends. This is not a bug in the optimizer; any code that violates the aliasing rules is illegal. (Note that this is not unique to GNU Fortran; any Fortran compiler that supports Cray pointers will “incorrectly” optimize code with illegal aliasing.)

There are a number of restrictions on the attributes that can be applied to Cray pointers and pointees. Pointees may not have the ALLOCATABLE, INTENT, OPTIONAL, DUMMY, TARGET, INTRINSIC, or POINTER attributes. Pointers may not have the DIMENSION, POINTER, TARGET, ALLOCATABLE, EXTERNAL, or INTRINSIC attributes, nor may they be function results. Pointees may not occur in more than one pointer statement. A pointee cannot be a pointer. Pointees cannot occur in equivalence, common, or data statements.

A Cray pointer may also point to a function or a subroutine. For example, the following excerpt is valid:

  implicit none
  external sub
  pointer (subptr,subpte)
  external subpte
  subptr = loc(sub)
  call subpte()
  [...]
  subroutine sub
  [...]
  end subroutine sub

A pointer may be modified during the course of a program, and this will change the location to which the pointee refers. However, when pointees are passed as arguments, they are treated as ordinary variables in the invoked function. Subsequent changes to the pointer will not change the base address of the array that was passed.


6.1.17 CONVERT specifier

GNU Fortran allows the conversion of unformatted data between little- and big-endian representation to facilitate moving of data between different systems. The conversion can be indicated with the CONVERT specifier on the OPEN statement. See GFORTRAN_CONVERT_UNIT—Set endianness for unformatted I/O, for an alternative way of specifying the data format via an environment variable.

Valid values for CONVERT are:

  • CONVERT='NATIVE' Use the native format. This is the default.
  • CONVERT='SWAP' Swap between little- and big-endian.
  • CONVERT='LITTLE_ENDIAN' Use the little-endian representation for unformatted files.
  • CONVERT='BIG_ENDIAN' Use the big-endian representation for unformatted files.

Using the option could look like this:

  open(file='big.dat',form='unformatted',access='sequential', &
       convert='big_endian')

The value of the conversion can be queried by using INQUIRE(CONVERT=ch). The values returned are 'BIG_ENDIAN' and 'LITTLE_ENDIAN'.

CONVERT works between big- and little-endian for INTEGER values of all supported kinds and for REAL on IEEE systems of kinds 4 and 8. Conversion between different “extended double” types on different architectures such as m68k and x86_64, which GNU Fortran supports as REAL(KIND=10) and REAL(KIND=16), will probably not work.

Note that the values specified via the GFORTRAN_CONVERT_UNIT environment variable will override the CONVERT specifier in the open statement. This is to give control over data formats to users who do not have the source code of their program available.

Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable.


6.1.18 OpenMP

OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C/C++ and Fortran on many architectures, including Unix and Microsoft Windows platforms. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior.

GNU Fortran strives to be compatible to the OpenMP Application Program Interface v4.5.

To enable the processing of the OpenMP directive !$omp in free-form source code; the c$omp, *$omp and !$omp directives in fixed form; the !$ conditional compilation sentinels in free form; and the c$, *$ and !$ sentinels in fixed form, gfortran needs to be invoked with the -fopenmp. This also arranges for automatic linking of the GNU Offloading and Multi Processing Runtime Library libgomp in GNU Offloading and Multi Processing Runtime Library.

The OpenMP Fortran runtime library routines are provided both in a form of a Fortran 90 module named omp_lib and in a form of a Fortran include file named omp_lib.h.

An example of a parallelized loop taken from Appendix A.1 of the OpenMP Application Program Interface v2.5:

SUBROUTINE A1(N, A, B)
  INTEGER I, N
  REAL B(N), A(N)
!$OMP PARALLEL DO !I is private by default
  DO I=2,N
    B(I) = (A(I) + A(I-1)) / 2.0
  ENDDO
!$OMP END PARALLEL DO
END SUBROUTINE A1

Please note:

  • -fopenmp implies -frecursive, i.e., all local arrays will be allocated on the stack. When porting existing code to OpenMP, this may lead to surprising results, especially to segmentation faults if the stacksize is limited.
  • On glibc-based systems, OpenMP enabled applications cannot be statically linked due to limitations of the underlying pthreads-implementation. It might be possible to get a working solution if -Wl,--whole-archive -lpthread -Wl,--no-whole-archive is added to the command line. However, this is not supported by gcc and thus not recommended.

6.1.19 OpenACC

OpenACC is an application programming interface (API) that supports offloading of code to accelerator devices. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior.

GNU Fortran strives to be compatible to the OpenACC Application Programming Interface v2.6.

To enable the processing of the OpenACC directive !$acc in free-form source code; the c$acc, *$acc and !$acc directives in fixed form; the !$ conditional compilation sentinels in free form; and the c$, *$ and !$ sentinels in fixed form, gfortran needs to be invoked with the -fopenacc. This also arranges for automatic linking of the GNU Offloading and Multi Processing Runtime Library libgomp in GNU Offloading and Multi Processing Runtime Library.

The OpenACC Fortran runtime library routines are provided both in a form of a Fortran 90 module named openacc and in a form of a Fortran include file named openacc_lib.h.


6.1.20 Argument list functions %VAL, %REF and %LOC

GNU Fortran supports argument list functions %VAL, %REF and %LOC statements, for backward compatibility with g77. It is recommended that these should be used only for code that is accessing facilities outside of GNU Fortran, such as operating system or windowing facilities. It is best to constrain such uses to isolated portions of a program–portions that deal specifically and exclusively with low-level, system-dependent facilities. Such portions might well provide a portable interface for use by the program as a whole, but are themselves not portable, and should be thoroughly tested each time they are rebuilt using a new compiler or version of a compiler.

%VAL passes a scalar argument by value, %REF passes it by reference and %LOC passes its memory location. Since gfortran already passes scalar arguments by reference, %REF is in effect a do-nothing. %LOC has the same effect as a Fortran pointer.

An example of passing an argument by value to a C subroutine foo.:

C
C prototype      void foo_ (float x);
C
      external foo
      real*4 x
      x = 3.14159
      call foo (%VAL (x))
      end

For details refer to the g77 manual https://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top.

Also, c_by_val.f and its partner c_by_val.c of the GNU Fortran testsuite are worth a look.


6.1.21 Read/Write after EOF marker

Some legacy codes rely on allowing READ or WRITE after the EOF file marker in order to find the end of a file. GNU Fortran normally rejects these codes with a run-time error message and suggests the user consider BACKSPACE or REWIND to properly position the file before the EOF marker. As an extension, the run-time error may be disabled using -std=legacy.


6.1.22 STRUCTURE and RECORD

Record structures are a pre-Fortran-90 vendor extension to create user-defined aggregate data types. Support for record structures in GNU Fortran can be enabled with the -fdec-structure compile flag. If you have a choice, you should instead use Fortran 90’s “derived types”, which have a different syntax.

In many cases, record structures can easily be converted to derived types. To convert, replace STRUCTURE /structure-name/ by TYPE type-name. Additionally, replace RECORD /structure-name/ by TYPE(type-name). Finally, in the component access, replace the period (.) by the percent sign (%).

Here is an example of code using the non portable record structure syntax:

! Declaring a structure named ``item'' and containing three fields:
! an integer ID, an description string and a floating-point price.
STRUCTURE /item/
  INTEGER id
  CHARACTER(LEN=200) description
  REAL price
END STRUCTURE

! Define two variables, an single record of type ``item''
! named ``pear'', and an array of items named ``store_catalog''
RECORD /item/ pear, store_catalog(100)

! We can directly access the fields of both variables
pear.id = 92316
pear.description = "juicy D'Anjou pear"
pear.price = 0.15
store_catalog(7).id = 7831
store_catalog(7).description = "milk bottle"
store_catalog(7).price = 1.2

! We can also manipulate the whole structure
store_catalog(12) = pear
print *, store_catalog(12)

This code can easily be rewritten in the Fortran 90 syntax as following:

! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
! ``TYPE name ... END TYPE''
TYPE item
  INTEGER id
  CHARACTER(LEN=200) description
  REAL price
END TYPE

! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
TYPE(item) pear, store_catalog(100)

! Instead of using a dot (.) to access fields of a record, the
! standard syntax uses a percent sign (%)
pear%id = 92316
pear%description = "juicy D'Anjou pear"
pear%price = 0.15
store_catalog(7)%id = 7831
store_catalog(7)%description = "milk bottle"
store_catalog(7)%price = 1.2

! Assignments of a whole variable do not change
store_catalog(12) = pear
print *, store_catalog(12)

GNU Fortran implements STRUCTURES like derived types with the following rules and exceptions:

  • Structures act like derived types with the SEQUENCE attribute. Otherwise they may contain no specifiers.
  • Structures may contain a special field with the name %FILL. This will create an anonymous component which cannot be accessed but occupies space just as if a component of the same type was declared in its place, useful for alignment purposes. As an example, the following structure will consist of at least sixteen bytes:
    structure /padded/
      character(4) start
      character(8) %FILL
      character(4) end
    end structure
    
  • Structures may share names with other symbols. For example, the following is invalid for derived types, but valid for structures:
    structure /header/
      ! ...
    end structure
    record /header/ header
    
  • Structure types may be declared nested within another parent structure. The syntax is:
    structure /type-name/
        ...
        structure [/<type-name>/] <field-list>
    ...
    

    The type name may be ommitted, in which case the structure type itself is anonymous, and other structures of the same type cannot be instantiated. The following shows some examples:

    structure /appointment/
      ! nested structure definition: app_time is an array of two 'time'
      structure /time/ app_time (2)
        integer(1) hour, minute
      end structure
      character(10) memo
    end structure
    
    ! The 'time' structure is still usable
    record /time/ now
    now = time(5, 30)
    
    ...
    
    structure /appointment/
      ! anonymous nested structure definition
      structure start, end
        integer(1) hour, minute
      end structure
      character(10) memo
    end structure
    
  • Structures may contain UNION blocks. For more detail see the section on UNION and MAP.
  • Structures support old-style initialization of components, like those described in Old-style variable initialization. For array initializers, an initializer may contain a repeat specification of the form <literal-integer> * <constant-initializer>. The value of the integer indicates the number of times to repeat the constant initializer when expanding the initializer list.

6.1.23 UNION and MAP

Unions are an old vendor extension which were commonly used with the non-standard STRUCTURE and RECORD extensions. Use of UNION and MAP is automatically enabled with -fdec-structure.

A UNION declaration occurs within a structure; within the definition of each union is a number of MAP blocks. Each MAP shares storage with its sibling maps (in the same union), and the size of the union is the size of the largest map within it, just as with unions in C. The major difference is that component references do not indicate which union or map the component is in (the compiler gets to figure that out).

Here is a small example:

structure /myunion/
union
  map
    character(2) w0, w1, w2
  end map
  map
    character(6) long
  end map
end union
end structure

record /myunion/ rec
! After this assignment...
rec.long = 'hello!'

! The following is true:
! rec.w0 === 'he'
! rec.w1 === 'll'
! rec.w2 === 'o!'

The two maps share memory, and the size of the union is ultimately six bytes:

0    1    2    3    4   5   6     Byte offset
-------------------------------
|    |    |    |    |    |    |
-------------------------------

^    W0   ^    W1   ^    W2   ^
 \-------/ \-------/ \-------/

^             LONG            ^
 \---------------------------/

Following is an example mirroring the layout of an Intel x86_64 register:

structure /reg/
  union ! U0                ! rax
    map
      character(16) rx
    end map
    map
      character(8) rh         ! rah
      union ! U1
        map
          character(8) rl     ! ral
        end map
        map
          character(8) ex     ! eax
        end map
        map
          character(4) eh     ! eah
          union ! U2
            map
              character(4) el ! eal
            end map
            map
              character(4) x  ! ax
            end map
            map
              character(2) h  ! ah
              character(2) l  ! al
            end map
          end union
        end map
      end union
    end map
  end union
end structure
record /reg/ a

! After this assignment...
a.rx     =     'AAAAAAAA.BBB.C.D'

! The following is true:
a.rx === 'AAAAAAAA.BBB.C.D'
a.rh === 'AAAAAAAA'
a.rl ===         '.BBB.C.D'
a.ex ===         '.BBB.C.D'
a.eh ===         '.BBB'
a.el ===             '.C.D'
a.x  ===             '.C.D'
a.h  ===             '.C'
a.l  ===               '.D'

6.1.24 Type variants for integer intrinsics

Similar to the D/C prefixes to real functions to specify the input/output types, GNU Fortran offers B/I/J/K prefixes to integer functions for compatibility with DEC programs. The types implied by each are:

B - INTEGER(kind=1)
I - INTEGER(kind=2)
J - INTEGER(kind=4)
K - INTEGER(kind=8)

GNU Fortran supports these with the flag -fdec-intrinsic-ints. Intrinsics for which prefixed versions are available and in what form are noted in Intrinsic Procedures. The complete list of supported intrinsics is here:

IntrinsicBIJK
ABS — Absolute valueBABSIIABSJIABSKIABS
BTEST — Bit test functionBBTESTBITESTBJTESTBKTEST
IAND — Bitwise logical andBIANDIIANDJIANDKIAND
IBCLR — Clear bitBBCLRIIBCLRJIBCLRKIBCLR
IBITS — Bit extractionBBITSIIBITSJIBITSKIBITS
IBSET — Set bitBBSETIIBSETJIBSETKIBSET
IEOR — Bitwise logical exclusive orBIEORIIEORJIEORKIEOR
IOR — Bitwise logical orBIORIIORJIORKIOR
ISHFT — Shift bitsBSHFTIISHFTJISHFTKISHFT
ISHFTC — Shift bits circularlyBSHFTCIISHFTCJISHFTCKISHFTC
MOD — Remainder functionBMODIMODJMODKMOD
NOT — Logical negationBNOTINOTJNOTKNOT
REAL — Convert to real type--FLOATIFLOATJFLOATK

6.1.25 AUTOMATIC and STATIC attributes

With -fdec-static GNU Fortran supports the DEC extended attributes STATIC and AUTOMATIC to provide explicit specification of entity storage. These follow the syntax of the Fortran standard SAVE attribute.

STATIC is exactly equivalent to SAVE, and specifies that an entity should be allocated in static memory. As an example, STATIC local variables will retain their values across multiple calls to a function.

Entities marked AUTOMATIC will be stack automatic whenever possible. AUTOMATIC is the default for local variables smaller than -fmax-stack-var-size, unless -fno-automatic is given. This attribute overrides -fno-automatic, -fmax-stack-var-size, and blanket SAVE statements.

Examples:

subroutine f
  integer, automatic :: i  ! automatic variable
  integer x, y             ! static variables
  save
  ...
endsubroutine
subroutine f
  integer a, b, c, x, y, z
  static :: x
  save y
  automatic z, c
  ! a, b, c, and z are automatic
  ! x and y are static
endsubroutine
! Compiled with -fno-automatic
subroutine f
  integer a, b, c, d
  automatic :: a
  ! a is automatic; b, c, and d are static
endsubroutine

6.1.26 Extended math intrinsics

GNU Fortran supports an extended list of mathematical intrinsics with the compile flag -fdec-math for compatability with legacy code. These intrinsics are described fully in Intrinsic Procedures where it is noted that they are extensions and should be avoided whenever possible.

Specifically, -fdec-math enables the COTAN — Cotangent function intrinsic, and trigonometric intrinsics which accept or produce values in degrees instead of radians. Here is a summary of the new intrinsics:

* Enabled with -fdec-math.

For advanced users, it may be important to know the implementation of these functions. They are simply wrappers around the standard radian functions, which have more accurate builtin versions. These functions convert their arguments (or results) to degrees (or radians) by taking the value modulus 360 (or 2*pi) and then multiplying it by a constant radian-to-degree (or degree-to-radian) factor, as appropriate. The factor is computed at compile-time as 180/pi (or pi/180).


6.1.27 Form feed as whitespace

Historically, legacy compilers allowed insertion of form feed characters (’\f’, ASCII 0xC) at the beginning of lines for formatted output to line printers, though the Fortran standard does not mention this. GNU Fortran supports the interpretation of form feed characters in source as whitespace for compatibility.


6.1.28 TYPE as an alias for PRINT

For compatibility, GNU Fortran will interpret TYPE statements as PRINT statements with the flag -fdec. With this flag asserted, the following two examples are equivalent:

TYPE *, 'hello world'
PRINT *, 'hello world'

6.1.29 %LOC as an rvalue

Normally %LOC is allowed only in parameter lists. However the intrinsic function LOC does the same thing, and is usable as the right-hand-side of assignments. For compatibility, GNU Fortran supports the use of %LOC as an alias for the builtin LOC with -std=legacy. With this feature enabled the following two examples are equivalent:

integer :: i, l
l = %loc(i)
call sub(l)
integer :: i
call sub(%loc(i))

6.1.30 .XOR. operator

GNU Fortran supports .XOR. as a logical operator with -std=legacy for compatibility with legacy code. .XOR. is equivalent to .NEQV.. That is, the output is true if and only if the inputs differ.


6.1.31 Bitwise logical operators

With -fdec, GNU Fortran relaxes the type constraints on logical operators to allow integer operands, and performs the corresponding bitwise operation instead. This flag is for compatibility only, and should be avoided in new code. Consider:

  INTEGER :: i, j
  i = z'33'
  j = z'cc'
  print *, i .AND. j

In this example, compiled with -fdec, GNU Fortran will replace the .AND. operation with a call to the intrinsic IAND — Bitwise logical and function, yielding the bitwise-and of i and j.

Note that this conversion will occur if at least one operand is of integral type. As a result, a logical operand will be converted to an integer when the other operand is an integer in a logical operation. In this case, .TRUE. is converted to 1 and .FALSE. to 0.

Here is the mapping of logical operator to bitwise intrinsic used with -fdec:

OperatorIntrinsicBitwise operation
.NOT.NOT — Logical negationcomplement
.AND.IAND — Bitwise logical andintersection
.OR.IOR — Bitwise logical orunion
.NEQV.IEOR — Bitwise logical exclusive orexclusive or
.EQV.NOT — Logical negation(IEOR — Bitwise logical exclusive or)complement of exclusive or

6.1.32 Extended I/O specifiers

GNU Fortran supports the additional legacy I/O specifiers CARRIAGECONTROL, READONLY, and SHARE with the compile flag -fdec, for compatibility.

CARRIAGECONTROL

The CARRIAGECONTROL specifier allows a user to control line termination settings between output records for an I/O unit. The specifier has no meaning for readonly files. When CARRAIGECONTROL is specified upon opening a unit for formatted writing, the exact CARRIAGECONTROL setting determines what characters to write between output records. The syntax is:

OPEN(..., CARRIAGECONTROL=cc)

Where cc is a character expression that evaluates to one of the following values:

'LIST'One line feed between records (default)
'FORTRAN'Legacy interpretation of the first character (see below)
'NONE'No separator between records

With CARRIAGECONTROL='FORTRAN', when a record is written, the first character of the input record is not written, and instead determines the output record separator as follows:

Leading characterMeaningOutput separating character(s)
'+'OverprintingCarriage return only
'-'New lineLine feed and carriage return
'0'Skip lineTwo line feeds and carriage return
'1'New pageForm feed and carriage return
'$'PromptingLine feed (no carriage return)
CHAR(0)Overprinting (no advance)None
READONLY

The READONLY specifier may be given upon opening a unit, and is equivalent to specifying ACTION='READ', except that the file may not be deleted on close (i.e. CLOSE with STATUS="DELETE"). The syntax is:

OPEN(..., READONLY)
SHARE

The SHARE specifier allows system-level locking on a unit upon opening it for controlled access from multiple processes/threads. The SHARE specifier has several forms:

OPEN(..., SHARE=sh)
OPEN(..., SHARED)
OPEN(..., NOSHARED)

Where sh in the first form is a character expression that evaluates to a value as seen in the table below. The latter two forms are aliases for particular values of sh:

Explicit formShort formMeaning
SHARE='DENYRW'NOSHAREDExclusive (write) lock
SHARE='DENYNONE'SHAREDShared (read) lock

In general only one process may hold an exclusive (write) lock for a given file at a time, whereas many processes may hold shared (read) locks for the same file.

The behavior of locking may vary with your operating system. On POSIX systems, locking is implemented with fcntl. Consult your corresponding operating system’s manual pages for further details. Locking via SHARE= is not supported on other systems.


6.1.33 Legacy PARAMETER statements

For compatibility, GNU Fortran supports legacy PARAMETER statements without parentheses with -std=legacy. A warning is emitted if used with -std=gnu, and an error is acknowledged with a real Fortran standard flag (-std=f95, etc...). These statements take the following form:

implicit real (E)
parameter e = 2.718282
real c
parameter c = 3.0e8

6.1.34 Default exponents

For compatibility, GNU Fortran supports a default exponent of zero in real constants with -fdec. For example, 9e would be interpreted as 9e0, rather than an error.


6.2 Extensions not implemented in GNU Fortran

The long history of the Fortran language, its wide use and broad userbase, the large number of different compiler vendors and the lack of some features crucial to users in the first standards have lead to the existence of a number of important extensions to the language. While some of the most useful or popular extensions are supported by the GNU Fortran compiler, not all existing extensions are supported. This section aims at listing these extensions and offering advice on how best make code that uses them running with the GNU Fortran compiler.


6.2.1 ENCODE and DECODE statements

GNU Fortran does not support the ENCODE and DECODE statements. These statements are best replaced by READ and WRITE statements involving internal files (CHARACTER variables and arrays), which have been part of the Fortran standard since Fortran 77. For example, replace a code fragment like

      INTEGER*1 LINE(80)
      REAL A, B, C
c     ... Code that sets LINE
      DECODE (80, 9000, LINE) A, B, C
 9000 FORMAT (1X, 3(F10.5))

with the following:

      CHARACTER(LEN=80) LINE
      REAL A, B, C
c     ... Code that sets LINE
      READ (UNIT=LINE, FMT=9000) A, B, C
 9000 FORMAT (1X, 3(F10.5))

Similarly, replace a code fragment like

      INTEGER*1 LINE(80)
      REAL A, B, C
c     ... Code that sets A, B and C
      ENCODE (80, 9000, LINE) A, B, C
 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))

with the following:

      CHARACTER(LEN=80) LINE
      REAL A, B, C
c     ... Code that sets A, B and C
      WRITE (UNIT=LINE, FMT=9000) A, B, C
 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))

6.2.2 Variable FORMAT expressions

A variable FORMAT expression is format statement which includes angle brackets enclosing a Fortran expression: FORMAT(I<N>). GNU Fortran does not support this legacy extension. The effect of variable format expressions can be reproduced by using the more powerful (and standard) combination of internal output and string formats. For example, replace a code fragment like this:

      WRITE(6,20) INT1
 20   FORMAT(I<N+1>)

with the following:

c     Variable declaration
      CHARACTER(LEN=20) FMT
c
c     Other code here...
c
      WRITE(FMT,'("(I", I0, ")")') N+1
      WRITE(6,FMT) INT1

or with:

c     Variable declaration
      CHARACTER(LEN=20) FMT
c
c     Other code here...
c
      WRITE(FMT,*) N+1
      WRITE(6,"(I" // ADJUSTL(FMT) // ")") INT1

6.2.3 Alternate complex function syntax

Some Fortran compilers, including g77, let the user declare complex functions with the syntax COMPLEX FUNCTION name*16(), as well as COMPLEX*16 FUNCTION name(). Both are non-standard, legacy extensions. gfortran accepts the latter form, which is more common, but not the former.


6.2.4 Volatile COMMON blocks

Some Fortran compilers, including g77, let the user declare COMMON with the VOLATILE attribute. This is invalid standard Fortran syntax and is not supported by gfortran. Note that gfortran accepts VOLATILE variables in COMMON blocks since revision 4.3.


6.2.5 OPEN( ... NAME=)

Some Fortran compilers, including g77, let the user declare OPEN( ... NAME=). This is invalid standard Fortran syntax and is not supported by gfortran. OPEN( ... NAME=) should be replaced with OPEN( ... FILE=).


6.2.6 Q edit descriptor

Some Fortran compilers provide the Q edit descriptor, which transfers the number of characters left within an input record into an integer variable.

A direct replacement of the Q edit descriptor is not available in gfortran. How to replicate its functionality using standard-conforming code depends on what the intent of the original code is.

Options to replace Q may be to read the whole line into a character variable and then counting the number of non-blank characters left using LEN_TRIM. Another method may be to use formatted stream, read the data up to the position where the Q descriptor occurred, use INQUIRE to get the file position, count the characters up to the next NEW_LINE and then start reading from the position marked previously.


7 Mixed-Language Programming

This chapter is about mixed-language interoperability, but also applies if one links Fortran code compiled by different compilers. In most cases, use of the C Binding features of the Fortran 2003 standard is sufficient, and their use is highly recommended.


7.1 Interoperability with C

Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a standardized way to generate procedure and derived-type declarations and global variables which are interoperable with C (ISO/IEC 9899:1999). The bind(C) attribute has been added to inform the compiler that a symbol shall be interoperable with C; also, some constraints are added. Note, however, that not all C features have a Fortran equivalent or vice versa. For instance, neither C’s unsigned integers nor C’s functions with variable number of arguments have an equivalent in Fortran.

Note that array dimensions are reversely ordered in C and that arrays in C always start with index 0 while in Fortran they start by default with 1. Thus, an array declaration A(n,m) in Fortran matches A[m][n] in C and accessing the element A(i,j) matches A[j-1][i-1]. The element following A(i,j) (C: A[j-1][i-1]; assuming i < n) in memory is A(i+1,j) (C: A[j-1][i]).


7.1.1 Intrinsic Types

In order to ensure that exactly the same variable type and kind is used in C and Fortran, the named constants shall be used which are defined in the ISO_C_BINDING intrinsic module. That module contains named constants for kind parameters and character named constants for the escape sequences in C. For a list of the constants, see ISO_C_BINDING.

For logical types, please note that the Fortran standard only guarantees interoperability between C99’s _Bool and Fortran’s C_Bool-kind logicals and C99 defines that true has the value 1 and false the value 0. Using any other integer value with GNU Fortran’s LOGICAL (with any kind parameter) gives an undefined result. (Passing other integer values than 0 and 1 to GCC’s _Bool is also undefined, unless the integer is explicitly or implicitly casted to _Bool.)


7.1.2 Derived Types and struct

For compatibility of derived types with struct, one needs to use the BIND(C) attribute in the type declaration. For instance, the following type declaration

 USE ISO_C_BINDING
 TYPE, BIND(C) :: myType
   INTEGER(C_INT) :: i1, i2
   INTEGER(C_SIGNED_CHAR) :: i3
   REAL(C_DOUBLE) :: d1
   COMPLEX(C_FLOAT_COMPLEX) :: c1
   CHARACTER(KIND=C_CHAR) :: str(5)
 END TYPE

matches the following struct declaration in C

 struct {
   int i1, i2;
   /* Note: "char" might be signed or unsigned.  */
   signed char i3;
   double d1;
   float _Complex c1;
   char str[5];
 } myType;

Derived types with the C binding attribute shall not have the sequence attribute, type parameters, the extends attribute, nor type-bound procedures. Every component must be of interoperable type and kind and may not have the pointer or allocatable attribute. The names of the components are irrelevant for interoperability.

As there exist no direct Fortran equivalents, neither unions nor structs with bit field or variable-length array members are interoperable.


7.1.3 Interoperable Global Variables

Variables can be made accessible from C using the C binding attribute, optionally together with specifying a binding name. Those variables have to be declared in the declaration part of a MODULE, be of interoperable type, and have neither the pointer nor the allocatable attribute.

  MODULE m
    USE myType_module
    USE ISO_C_BINDING
    integer(C_INT), bind(C, name="_MyProject_flags") :: global_flag
    type(myType), bind(C) :: tp
  END MODULE

Here, _MyProject_flags is the case-sensitive name of the variable as seen from C programs while global_flag is the case-insensitive name as seen from Fortran. If no binding name is specified, as for tp, the C binding name is the (lowercase) Fortran binding name. If a binding name is specified, only a single variable may be after the double colon. Note of warning: You cannot use a global variable to access errno of the C library as the C standard allows it to be a macro. Use the IERRNO intrinsic (GNU extension) instead.


7.1.4 Interoperable Subroutines and Functions

Subroutines and functions have to have the BIND(C) attribute to be compatible with C. The dummy argument declaration is relatively straightforward. However, one needs to be careful because C uses call-by-value by default while Fortran behaves usually similar to call-by-reference. Furthermore, strings and pointers are handled differently. Note that in Fortran 2003 and 2008 only explicit size and assumed-size arrays are supported but not assumed-shape or deferred-shape (i.e. allocatable or pointer) arrays. However, those are allowed since the Technical Specification 29113, see Further Interoperability of Fortran with C

To pass a variable by value, use the VALUE attribute. Thus, the following C prototype

int func(int i, int *j)

matches the Fortran declaration

  integer(c_int) function func(i,j)
    use iso_c_binding, only: c_int
    integer(c_int), VALUE :: i
    integer(c_int) :: j

Note that pointer arguments also frequently need the VALUE attribute, see Working with Pointers.

Strings are handled quite differently in C and Fortran. In C a string is a NUL-terminated array of characters while in Fortran each string has a length associated with it and is thus not terminated (by e.g. NUL). For example, if one wants to use the following C function,

  #include <stdio.h>
  void print_C(char *string) /* equivalent: char string[]  */
  {
     printf("%s\n", string);
  }

to print “Hello World” from Fortran, one can call it using

  use iso_c_binding, only: C_CHAR, C_NULL_CHAR
  interface
    subroutine print_c(string) bind(C, name="print_C")
      use iso_c_binding, only: c_char
      character(kind=c_char) :: string(*)
    end subroutine print_c
  end interface
  call print_c(C_CHAR_"Hello World"//C_NULL_CHAR)

As the example shows, one needs to ensure that the string is NUL terminated. Additionally, the dummy argument string of print_C is a length-one assumed-size array; using character(len=*) is not allowed. The example above uses c_char_"Hello World" to ensure the string literal has the right type; typically the default character kind and c_char are the same and thus "Hello World" is equivalent. However, the standard does not guarantee this.

The use of strings is now further illustrated using the C library function strncpy, whose prototype is

  char *strncpy(char *restrict s1, const char *restrict s2, size_t n);

The function strncpy copies at most n characters from string s2 to s1 and returns s1. In the following example, we ignore the return value:

  use iso_c_binding
  implicit none
  character(len=30) :: str,str2
  interface
    ! Ignore the return value of strncpy -> subroutine
    ! "restrict" is always assumed if we do not pass a pointer
    subroutine strncpy(dest, src, n) bind(C)
      import
      character(kind=c_char),  intent(out) :: dest(*)
      character(kind=c_char),  intent(in)  :: src(*)
      integer(c_size_t), value, intent(in) :: n
    end subroutine strncpy
  end interface
  str = repeat('X',30) ! Initialize whole string with 'X'
  call strncpy(str, c_char_"Hello World"//C_NULL_CHAR, &
               len(c_char_"Hello World",kind=c_size_t))
  print '(a)', str ! prints: "Hello WorldXXXXXXXXXXXXXXXXXXX"
  end

The intrinsic procedures are described in Intrinsic Procedures.


7.1.5 Working with Pointers

C pointers are represented in Fortran via the special opaque derived type type(c_ptr) (with private components). Thus one needs to use intrinsic conversion procedures to convert from or to C pointers.

For some applications, using an assumed type (TYPE(*)) can be an alternative to a C pointer; see Further Interoperability of Fortran with C.

For example,

  use iso_c_binding
  type(c_ptr) :: cptr1, cptr2
  integer, target :: array(7), scalar
  integer, pointer :: pa(:), ps
  cptr1 = c_loc(array(1)) ! The programmer needs to ensure that the
                          ! array is contiguous if required by the C
                          ! procedure
  cptr2 = c_loc(scalar)
  call c_f_pointer(cptr2, ps)
  call c_f_pointer(cptr2, pa, shape=[7])

When converting C to Fortran arrays, the one-dimensional SHAPE argument has to be passed.

If a pointer is a dummy-argument of an interoperable procedure, it usually has to be declared using the VALUE attribute. void* matches TYPE(C_PTR), VALUE, while TYPE(C_PTR) alone matches void**.

Procedure pointers are handled analogously to pointers; the C type is TYPE(C_FUNPTR) and the intrinsic conversion procedures are C_F_PROCPOINTER and C_FUNLOC.

Let us consider two examples of actually passing a procedure pointer from C to Fortran and vice versa. Note that these examples are also very similar to passing ordinary pointers between both languages. First, consider this code in C:

/* Procedure implemented in Fortran.  */
void get_values (void (*)(double));

/* Call-back routine we want called from Fortran.  */
void
print_it (double x)
{
  printf ("Number is %f.\n", x);
}

/* Call Fortran routine and pass call-back to it.  */
void
foobar ()
{
  get_values (&print_it);
}

A matching implementation for get_values in Fortran, that correctly receives the procedure pointer from C and is able to call it, is given in the following MODULE:

MODULE m
  IMPLICIT NONE

  ! Define interface of call-back routine.
  ABSTRACT INTERFACE
    SUBROUTINE callback (x)
      USE, INTRINSIC :: ISO_C_BINDING
      REAL(KIND=C_DOUBLE), INTENT(IN), VALUE :: x
    END SUBROUTINE callback
  END INTERFACE

CONTAINS

  ! Define C-bound procedure.
  SUBROUTINE get_values (cproc) BIND(C)
    USE, INTRINSIC :: ISO_C_BINDING
    TYPE(C_FUNPTR), INTENT(IN), VALUE :: cproc

    PROCEDURE(callback), POINTER :: proc

    ! Convert C to Fortran procedure pointer.
    CALL C_F_PROCPOINTER (cproc, proc)

    ! Call it.
    CALL proc (1.0_C_DOUBLE)
    CALL proc (-42.0_C_DOUBLE)
    CALL proc (18.12_C_DOUBLE)
  END SUBROUTINE get_values

END MODULE m

Next, we want to call a C routine that expects a procedure pointer argument and pass it a Fortran procedure (which clearly must be interoperable!). Again, the C function may be:

int
call_it (int (*func)(int), int arg)
{
  return func (arg);
}

It can be used as in the following Fortran code:

MODULE m
  USE, INTRINSIC :: ISO_C_BINDING
  IMPLICIT NONE

  ! Define interface of C function.
  INTERFACE
    INTEGER(KIND=C_INT) FUNCTION call_it (func, arg) BIND(C)
      USE, INTRINSIC :: ISO_C_BINDING
      TYPE(C_FUNPTR), INTENT(IN), VALUE :: func
      INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
    END FUNCTION call_it
  END INTERFACE

CONTAINS

  ! Define procedure passed to C function.
  ! It must be interoperable!
  INTEGER(KIND=C_INT) FUNCTION double_it (arg) BIND(C)
    INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
    double_it = arg + arg
  END FUNCTION double_it

  ! Call C function.
  SUBROUTINE foobar ()
    TYPE(C_FUNPTR) :: cproc
    INTEGER(KIND=C_INT) :: i

    ! Get C procedure pointer.
    cproc = C_FUNLOC (double_it)

    ! Use it.
    DO i = 1_C_INT, 10_C_INT
      PRINT *, call_it (cproc, i)
    END DO
  END SUBROUTINE foobar

END MODULE m

7.1.6 Further Interoperability of Fortran with C

The Technical Specification ISO/IEC TS 29113:2012 on further interoperability of Fortran with C extends the interoperability support of Fortran 2003 and Fortran 2008. Besides removing some restrictions and constraints, it adds assumed-type (TYPE(*)) and assumed-rank (dimension) variables and allows for interoperability of assumed-shape, assumed-rank and deferred-shape arrays, including allocatables and pointers.

Note: Currently, GNU Fortran does not use internally the array descriptor (dope vector) as specified in the Technical Specification, but uses an array descriptor with different fields. Assumed type and assumed rank formal arguments are converted in the library to the specified form. The ISO_Fortran_binding API functions (also Fortran 2018 18.4) are implemented in libgfortran. Alternatively, the Chasm Language Interoperability Tools, http://chasm-interop.sourceforge.net/, provide an interface to GNU Fortran’s array descriptor.

The Technical Specification adds the following new features, which are supported by GNU Fortran:

  • The ASYNCHRONOUS attribute has been clarified and extended to allow its use with asynchronous communication in user-provided libraries such as in implementations of the Message Passing Interface specification.
  • Many constraints have been relaxed, in particular for the C_LOC and C_F_POINTER intrinsics.
  • The OPTIONAL attribute is now allowed for dummy arguments; an absent argument matches a NULL pointer.
  • Assumed types (TYPE(*)) have been added, which may only be used for dummy arguments. They are unlimited polymorphic but contrary to CLASS(*) they do not contain any type information, similar to C’s void * pointers. Expressions of any type and kind can be passed; thus, it can be used as replacement for TYPE(C_PTR), avoiding the use of C_LOC in the caller.

    Note, however, that TYPE(*) only accepts scalar arguments, unless the DIMENSION is explicitly specified. As DIMENSION(*) only supports array (including array elements) but no scalars, it is not a full replacement for C_LOC. On the other hand, assumed-type assumed-rank dummy arguments (TYPE(*), DIMENSION(..)) allow for both scalars and arrays, but require special code on the callee side to handle the array descriptor.

  • Assumed-rank arrays (DIMENSION(..)) as dummy argument allow that scalars and arrays of any rank can be passed as actual argument. As the Technical Specification does not provide for direct means to operate with them, they have to be used either from the C side or be converted using C_LOC and C_F_POINTER to scalars or arrays of a specific rank. The rank can be determined using the RANK intrinisic.

Currently unimplemented:

  • GNU Fortran always uses an array descriptor, which does not match the one of the Technical Specification. The ISO_Fortran_binding.h header file and the C functions it specifies are not available.
  • Using assumed-shape, assumed-rank and deferred-shape arrays in BIND(C) procedures is not fully supported. In particular, C interoperable strings of other length than one are not supported as this requires the new array descriptor.

7.2 GNU Fortran Compiler Directives


7.2.1 ATTRIBUTES directive

The Fortran standard describes how a conforming program shall behave; however, the exact implementation is not standardized. In order to allow the user to choose specific implementation details, compiler directives can be used to set attributes of variables and procedures which are not part of the standard. Whether a given attribute is supported and its exact effects depend on both the operating system and on the processor; see C Extensions in Using the GNU Compiler Collection (GCC) for details.

For procedures and procedure pointers, the following attributes can be used to change the calling convention:

  • CDECL – standard C calling convention
  • STDCALL – convention where the called procedure pops the stack
  • FASTCALL – part of the arguments are passed via registers instead using the stack

Besides changing the calling convention, the attributes also influence the decoration of the symbol name, e.g., by a leading underscore or by a trailing at-sign followed by the number of bytes on the stack. When assigning a procedure to a procedure pointer, both should use the same calling convention.

On some systems, procedures and global variables (module variables and COMMON blocks) need special handling to be accessible when they are in a shared library. The following attributes are available:

  • DLLEXPORT – provide a global pointer to a pointer in the DLL
  • DLLIMPORT – reference the function or variable using a global pointer

For dummy arguments, the NO_ARG_CHECK attribute can be used; in other compilers, it is also known as IGNORE_TKR. For dummy arguments with this attribute actual arguments of any type and kind (similar to TYPE(*)), scalars and arrays of any rank (no equivalent in Fortran standard) are accepted. As with TYPE(*), the argument is unlimited polymorphic and no type information is available. Additionally, the argument may only be passed to dummy arguments with the NO_ARG_CHECK attribute and as argument to the PRESENT intrinsic function and to C_LOC of the ISO_C_BINDING module.

Variables with NO_ARG_CHECK attribute shall be of assumed-type (TYPE(*); recommended) or of type INTEGER, LOGICAL, REAL or COMPLEX. They shall not have the ALLOCATE, CODIMENSION, INTENT(OUT), POINTER or VALUE attribute; furthermore, they shall be either scalar or of assumed-size (dimension(*)). As TYPE(*), the NO_ARG_CHECK attribute requires an explicit interface.

  • NO_ARG_CHECK – disable the type, kind and rank checking
  • DEPRECATED – print a warning when using a such-tagged deprecated procedure, variable or parameter; the warning can be suppressed with -Wno-deprecated-declarations.

The attributes are specified using the syntax

!GCC$ ATTRIBUTES attribute-list :: variable-list

where in free-form source code only whitespace is allowed before !GCC$ and in fixed-form source code !GCC$, cGCC$ or *GCC$ shall start in the first column.

For procedures, the compiler directives shall be placed into the body of the procedure; for variables and procedure pointers, they shall be in the same declaration part as the variable or procedure pointer.


7.2.2 UNROLL directive

The syntax of the directive is

!GCC$ unroll N

You can use this directive to control how many times a loop should be unrolled. It must be placed immediately before a DO loop and applies only to the loop that follows. N is an integer constant specifying the unrolling factor. The values of 0 and 1 block any unrolling of the loop.


7.2.3 BUILTIN directive

The syntax of the directive is

!GCC$ BUILTIN (B) attributes simd FLAGS IF('target')

You can use this directive to define which middle-end built-ins provide vector implementations. B is name of the middle-end built-in. FLAGS are optional and must be either "(inbranch)" or "(notinbranch)". IF statement is optional and is used to filter multilib ABIs for the built-in that should be vectorized. Example usage:

!GCC$ builtin (sinf) attributes simd (notinbranch) if('x86_64')

The purpose of the directive is to provide an API among the GCC compiler and the GNU C Library which would define vector implementations of math routines.


7.2.4 IVDEP directive

The syntax of the directive is

!GCC$ ivdep

This directive tells the compiler to ignore vector dependencies in the following loop. It must be placed immediately before a DO loop and applies only to the loop that follows.

Sometimes the compiler may not have sufficient information to decide whether a particular loop is vectorizable due to potential dependencies between iterations. The purpose of the directive is to tell the compiler that vectorization is safe.

This directive is intended for annotation of existing code. For new code it is recommended to consider OpenMP SIMD directives as potential alternative.


7.2.5 VECTOR directive

The syntax of the directive is

!GCC$ vector

This directive tells the compiler to vectorize the following loop. It must be placed immediately before a DO loop and applies only to the loop that follows.


7.2.6 NOVECTOR directive

The syntax of the directive is

!GCC$ novector

This directive tells the compiler to not vectorize the following loop. It must be placed immediately before a DO loop and applies only to the loop that follows.


7.3 Non-Fortran Main Program

Even if you are doing mixed-language programming, it is very likely that you do not need to know or use the information in this section. Since it is about the internal structure of GNU Fortran, it may also change in GCC minor releases.

When you compile a PROGRAM with GNU Fortran, a function with the name main (in the symbol table of the object file) is generated, which initializes the libgfortran library and then calls the actual program which uses the name MAIN__, for historic reasons. If you link GNU Fortran compiled procedures to, e.g., a C or C++ program or to a Fortran program compiled by a different compiler, the libgfortran library is not initialized and thus a few intrinsic procedures do not work properly, e.g. those for obtaining the command-line arguments.

Therefore, if your PROGRAM is not compiled with GNU Fortran and the GNU Fortran compiled procedures require intrinsics relying on the library initialization, you need to initialize the library yourself. Using the default options, gfortran calls _gfortran_set_args and _gfortran_set_options. The initialization of the former is needed if the called procedures access the command line (and for backtracing); the latter sets some flags based on the standard chosen or to enable backtracing. In typical programs, it is not necessary to call any initialization function.

If your PROGRAM is compiled with GNU Fortran, you shall not call any of the following functions. The libgfortran initialization functions are shown in C syntax but using C bindings they are also accessible from Fortran.


7.3.1 _gfortran_set_args — Save command-line arguments

Description:

_gfortran_set_args saves the command-line arguments; this initialization is required if any of the command-line intrinsics is called. Additionally, it shall be called if backtracing is enabled (see _gfortran_set_options).

Syntax:

void _gfortran_set_args (int argc, char *argv[])

Arguments:
argcnumber of command line argument strings
argvthe command-line argument strings; argv[0] is the pathname of the executable itself.
Example:
int main (int argc, char *argv[])
{
  /* Initialize libgfortran.  */
  _gfortran_set_args (argc, argv);
  return 0;
}

7.3.2 _gfortran_set_options — Set library option flags

Description:

_gfortran_set_options sets several flags related to the Fortran standard to be used, whether backtracing should be enabled and whether range checks should be performed. The syntax allows for upward compatibility since the number of passed flags is specified; for non-passed flags, the default value is used. See also see Options for code generation conventions. Please note that not all flags are actually used.

Syntax:

void _gfortran_set_options (int num, int options[])

Arguments:
numnumber of options passed
argvThe list of flag values
option flag list:
option[0]Allowed standard; can give run-time errors if e.g. an input-output edit descriptor is invalid in a given standard. Possible values are (bitwise or-ed) GFC_STD_F77 (1), GFC_STD_F95_OBS (2), GFC_STD_F95_DEL (4), GFC_STD_F95 (8), GFC_STD_F2003 (16), GFC_STD_GNU (32), GFC_STD_LEGACY (64), GFC_STD_F2008 (128), GFC_STD_F2008_OBS (256), GFC_STD_F2008_TS (512), GFC_STD_F2018 (1024), GFC_STD_F2018_OBS (2048), and GFC_STD=F2018_DEL (4096). Default: GFC_STD_F95_OBS | GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003 | GFC_STD_F2008 | GFC_STD_F2008_TS | GFC_STD_F2008_OBS | GFC_STD_F77 | GFC_STD_F2018 | GFC_STD_F2018_OBS | GFC_STD_F2018_DEL | GFC_STD_GNU | GFC_STD_LEGACY.
option[1]Standard-warning flag; prints a warning to standard error. Default: GFC_STD_F95_DEL | GFC_STD_LEGACY.
option[2]If non zero, enable pedantic checking. Default: off.
option[3]Unused.
option[4]If non zero, enable backtracing on run-time errors. Default: off. (Default in the compiler: on.) Note: Installs a signal handler and requires command-line initialization using _gfortran_set_args.
option[5]If non zero, supports signed zeros. Default: enabled.
option[6]Enables run-time checking. Possible values are (bitwise or-ed): GFC_RTCHECK_BOUNDS (1), GFC_RTCHECK_ARRAY_TEMPS (2), GFC_RTCHECK_RECURSION (4), GFC_RTCHECK_DO (8), GFC_RTCHECK_POINTER (16), GFC_RTCHECK_MEM (32), GFC_RTCHECK_BITS (64). Default: disabled.
option[7]Unused.
option[8]Show a warning when invoking STOP and ERROR STOP if a floating-point exception occurred. Possible values are (bitwise or-ed) GFC_FPE_INVALID (1), GFC_FPE_DENORMAL (2), GFC_FPE_ZERO (4), GFC_FPE_OVERFLOW (8), GFC_FPE_UNDERFLOW (16), GFC_FPE_INEXACT (32). Default: None (0). (Default in the compiler: GFC_FPE_INVALID | GFC_FPE_DENORMAL | GFC_FPE_ZERO | GFC_FPE_OVERFLOW | GFC_FPE_UNDERFLOW.)
Example:
  /* Use gfortran 4.9 default options.  */
  static int options[] = {68, 511, 0, 0, 1, 1, 0, 0, 31};
  _gfortran_set_options (9, &options);

7.3.3 _gfortran_set_convert — Set endian conversion

Description:

_gfortran_set_convert set the representation of data for unformatted files.

Syntax:

void _gfortran_set_convert (int conv)

Arguments:
convEndian conversion, possible values: GFC_CONVERT_NATIVE (0, default), GFC_CONVERT_SWAP (1), GFC_CONVERT_BIG (2), GFC_CONVERT_LITTLE (3).
Example:
int main (int argc, char *argv[])
{
  /* Initialize libgfortran.  */
  _gfortran_set_args (argc, argv);
  _gfortran_set_convert (1);
  return 0;
}

7.3.4 _gfortran_set_record_marker — Set length of record markers

Description:

_gfortran_set_record_marker sets the length of record markers for unformatted files.

Syntax:

void _gfortran_set_record_marker (int val)

Arguments:
valLength of the record marker; valid values are 4 and 8. Default is 4.
Example:
int main (int argc, char *argv[])
{
  /* Initialize libgfortran.  */
  _gfortran_set_args (argc, argv);
  _gfortran_set_record_marker (8);
  return 0;
}

7.3.5 _gfortran_set_fpe — Enable floating point exception traps

Description:

_gfortran_set_fpe enables floating point exception traps for the specified exceptions. On most systems, this will result in a SIGFPE signal being sent and the program being aborted.

Syntax:

void _gfortran_set_fpe (int val)

Arguments:
option[0]IEEE exceptions. Possible values are (bitwise or-ed) zero (0, default) no trapping, GFC_FPE_INVALID (1), GFC_FPE_DENORMAL (2), GFC_FPE_ZERO (4), GFC_FPE_OVERFLOW (8), GFC_FPE_UNDERFLOW (16), and GFC_FPE_INEXACT (32).
Example:
int main (int argc, char *argv[])
{
  /* Initialize libgfortran.  */
  _gfortran_set_args (argc, argv);
  /* FPE for invalid operations such as SQRT(-1.0).  */
  _gfortran_set_fpe (1);
  return 0;
}

7.3.6 _gfortran_set_max_subrecord_length — Set subrecord length

Description:

_gfortran_set_max_subrecord_length set the maximum length for a subrecord. This option only makes sense for testing and debugging of unformatted I/O.

Syntax:

void _gfortran_set_max_subrecord_length (int val)

Arguments:
valthe maximum length for a subrecord; the maximum permitted value is 2147483639, which is also the default.
Example:
int main (int argc, char *argv[])
{
  /* Initialize libgfortran.  */
  _gfortran_set_args (argc, argv);
  _gfortran_set_max_subrecord_length (8);
  return 0;
}

7.4 Naming and argument-passing conventions

This section gives an overview about the naming convention of procedures and global variables and about the argument passing conventions used by GNU Fortran. If a C binding has been specified, the naming convention and some of the argument-passing conventions change. If possible, mixed-language and mixed-compiler projects should use the better defined C binding for interoperability. See see Interoperability with C.


7.4.1 Naming conventions

According the Fortran standard, valid Fortran names consist of a letter between A to Z, a to z, digits 0, 1 to 9 and underscores (_) with the restriction that names may only start with a letter. As vendor extension, the dollar sign ($) is additionally permitted with the option -fdollar-ok, but not as first character and only if the target system supports it.

By default, the procedure name is the lower-cased Fortran name with an appended underscore (_); using -fno-underscoring no underscore is appended while -fsecond-underscore appends two underscores. Depending on the target system and the calling convention, the procedure might be additionally dressed; for instance, on 32bit Windows with stdcall, an at-sign @ followed by an integer number is appended. For the changing the calling convention, see see GNU Fortran Compiler Directives.

For common blocks, the same convention is used, i.e. by default an underscore is appended to the lower-cased Fortran name. Blank commons have the name __BLNK__.

For procedures and variables declared in the specification space of a module, the name is formed by __, followed by the lower-cased module name, _MOD_, and the lower-cased Fortran name. Note that no underscore is appended.


7.4.2 Argument passing conventions

Subroutines do not return a value (matching C99’s void) while functions either return a value as specified in the platform ABI or the result variable is passed as hidden argument to the function and no result is returned. A hidden result variable is used when the result variable is an array or of type CHARACTER.

Arguments are passed according to the platform ABI. In particular, complex arguments might not be compatible to a struct with two real components for the real and imaginary part. The argument passing matches the one of C99’s _Complex. Functions with scalar complex result variables return their value and do not use a by-reference argument. Note that with the -ff2c option, the argument passing is modified and no longer completely matches the platform ABI. Some other Fortran compilers use f2c semantic by default; this might cause problems with interoperablility.

GNU Fortran passes most arguments by reference, i.e. by passing a pointer to the data. Note that the compiler might use a temporary variable into which the actual argument has been copied, if required semantically (copy-in/copy-out).

For arguments with ALLOCATABLE and POINTER attribute (including procedure pointers), a pointer to the pointer is passed such that the pointer address can be modified in the procedure.

For dummy arguments with the VALUE attribute: Scalar arguments of the type INTEGER, LOGICAL, REAL and COMPLEX are passed by value according to the platform ABI. (As vendor extension and not recommended, using %VAL() in the call to a procedure has the same effect.) For TYPE(C_PTR) and procedure pointers, the pointer itself is passed such that it can be modified without affecting the caller.

For Boolean (LOGICAL) arguments, please note that GCC expects only the integer value 0 and 1. If a GNU Fortran LOGICAL variable contains another integer value, the result is undefined. As some other Fortran compilers use -1 for .TRUE., extra care has to be taken – such as passing the value as INTEGER. (The same value restriction also applies to other front ends of GCC, e.g. to GCC’s C99 compiler for _Bool or GCC’s Ada compiler for Boolean.)

For arguments of CHARACTER type, the character length is passed as a hidden argument at the end of the argument list. For deferred-length strings, the value is passed by reference, otherwise by value. The character length has the C type size_t (or INTEGER(kind=C_SIZE_T) in Fortran). Note that this is different to older versions of the GNU Fortran compiler, where the type of the hidden character length argument was a C int. In order to retain compatibility with older versions, one can e.g. for the following Fortran procedure

subroutine fstrlen (s, a)
   character(len=*) :: s
   integer :: a
   print*, len(s)
end subroutine fstrlen

define the corresponding C prototype as follows:

#if __GNUC__ > 7
typedef size_t fortran_charlen_t;
#else
typedef int fortran_charlen_t;
#endif

void fstrlen_ (char*, int*, fortran_charlen_t);

In order to avoid such compiler-specific details, for new code it is instead recommended to use the ISO_C_BINDING feature.

Note with C binding, CHARACTER(len=1) result variables are returned according to the platform ABI and no hidden length argument is used for dummy arguments; with VALUE, those variables are passed by value.

For OPTIONAL dummy arguments, an absent argument is denoted by a NULL pointer, except for scalar dummy arguments of type INTEGER, LOGICAL, REAL and COMPLEX which have the VALUE attribute. For those, a hidden Boolean argument (logical(kind=C_bool),value) is used to indicate whether the argument is present.

Arguments which are assumed-shape, assumed-rank or deferred-rank arrays or, with -fcoarray=lib, allocatable scalar coarrays use an array descriptor. All other arrays pass the address of the first element of the array. With -fcoarray=lib, the token and the offset belonging to nonallocatable coarrays dummy arguments are passed as hidden argument along the character length hidden arguments. The token is an opaque pointer identifying the coarray and the offset is a passed-by-value integer of kind C_PTRDIFF_T, denoting the byte offset between the base address of the coarray and the passed scalar or first element of the passed array.

The arguments are passed in the following order

  • Result variable, when the function result is passed by reference
  • Character length of the function result, if it is a of type CHARACTER and no C binding is used
  • The arguments in the order in which they appear in the Fortran declaration
  • The the present status for optional arguments with value attribute, which are internally passed by value
  • The character length and/or coarray token and offset for the first argument which is a CHARACTER or a nonallocatable coarray dummy argument, followed by the hidden arguments of the next dummy argument of such a type

8 Coarray Programming


8.1 Type and enum ABI Documentation


8.1.1 caf_token_t

Typedef of type void * on the compiler side. Can be any data type on the library side.


8.1.2 caf_register_t

Indicates which kind of coarray variable should be registered.

typedef enum caf_register_t {
  CAF_REGTYPE_COARRAY_STATIC,
  CAF_REGTYPE_COARRAY_ALLOC,
  CAF_REGTYPE_LOCK_STATIC,
  CAF_REGTYPE_LOCK_ALLOC,
  CAF_REGTYPE_CRITICAL,
  CAF_REGTYPE_EVENT_STATIC,
  CAF_REGTYPE_EVENT_ALLOC,
  CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY,
  CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY
}
caf_register_t;

The values CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY and CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY are for allocatable components in derived type coarrays only. The first one sets up the token without allocating memory for allocatable component. The latter one only allocates the memory for an allocatable component in a derived type coarray. The token needs to be setup previously by the REGISTER_ONLY. This allows to have allocatable components un-allocated on some images. The status whether an allocatable component is allocated on a remote image can be queried by _caf_is_present which used internally by the ALLOCATED intrinsic.


8.1.3 caf_deregister_t

typedef enum caf_deregister_t {
  CAF_DEREGTYPE_COARRAY_DEREGISTER,
  CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY
}
caf_deregister_t;

Allows to specifiy the type of deregistration of a coarray object. The CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY flag is only allowed for allocatable components in derived type coarrays.


8.1.4 caf_reference_t

The structure used for implementing arbitrary reference chains. A CAF_REFERENCE_T allows to specify a component reference or any kind of array reference of any rank supported by gfortran. For array references all kinds as known by the compiler/Fortran standard are supported indicated by a MODE.

typedef enum caf_ref_type_t {
  /* Reference a component of a derived type, either regular one or an
     allocatable or pointer type.  For regular ones idx in caf_reference_t is
     set to -1.  */
  CAF_REF_COMPONENT,
  /* Reference an allocatable array.  */
  CAF_REF_ARRAY,
  /* Reference a non-allocatable/non-pointer array.  I.e., the coarray object
     has no array descriptor associated and the addressing is done
     completely using the ref.  */
  CAF_REF_STATIC_ARRAY
} caf_ref_type_t;
typedef enum caf_array_ref_t {
  /* No array ref.  This terminates the array ref.  */
  CAF_ARR_REF_NONE = 0,
  /* Reference array elements given by a vector.  Only for this mode
     caf_reference_t.u.a.dim[i].v is valid.  */
  CAF_ARR_REF_VECTOR,
  /* A full array ref (:).  */
  CAF_ARR_REF_FULL,
  /* Reference a range on elements given by start, end and stride.  */
  CAF_ARR_REF_RANGE,
  /* Only a single item is referenced given in the start member.  */
  CAF_ARR_REF_SINGLE,
  /* An array ref of the kind (i:), where i is an arbitrary valid index in the
     array.  The index i is given in the start member.  */
  CAF_ARR_REF_OPEN_END,
  /* An array ref of the kind (:i), where the lower bound of the array ref
     is given by the remote side.  The index i is given in the end member.  */
  CAF_ARR_REF_OPEN_START
} caf_array_ref_t;
/* References to remote components of a derived type.  */
typedef struct caf_reference_t {
  /* A pointer to the next ref or NULL.  */
  struct caf_reference_t *next;
  /* The type of the reference.  */
  /* caf_ref_type_t, replaced by int to allow specification in fortran FE.  */
  int type;
  /* The size of an item referenced in bytes.  I.e. in an array ref this is
     the factor to advance the array pointer with to get to the next item.
     For component refs this gives just the size of the element referenced.  */
  size_t item_size;
  union {
    struct {
      /* The offset (in bytes) of the component in the derived type.
         Unused for allocatable or pointer components.  */
      ptrdiff_t offset;
      /* The offset (in bytes) to the caf_token associated with this
         component.  NULL, when not allocatable/pointer ref.  */
      ptrdiff_t caf_token_offset;
    } c;
    struct {
      /* The mode of the array ref.  See CAF_ARR_REF_*.  */
      /* caf_array_ref_t, replaced by unsigend char to allow specification in
         fortran FE.  */
     unsigned char mode[GFC_MAX_DIMENSIONS];
      /* The type of a static array.  Unset for array's with descriptors.  */
      int static_array_type;
      /* Subscript refs (s) or vector refs (v).  */
      union {
        struct {
          /* The start and end boundary of the ref and the stride.  */
          index_type start, end, stride;
        } s;
        struct {
          /* nvec entries of kind giving the elements to reference.  */
          void *vector;
          /* The number of entries in vector.  */
          size_t nvec;
          /* The integer kind used for the elements in vector.  */
          int kind;
        } v;
      } dim[GFC_MAX_DIMENSIONS];
    } a;
  } u;
} caf_reference_t;

The references make up a single linked list of reference operations. The NEXT member links to the next reference or NULL to indicate the end of the chain. Component and array refs can be arbitrarily mixed as long as they comply to the Fortran standard.

NOTES The member STATIC_ARRAY_TYPE is used only when the TYPE is CAF_REF_STATIC_ARRAY. The member gives the type of the data referenced. Because no array descriptor is available for a descriptor-less array and type conversion still needs to take place the type is transported here.

At the moment CAF_ARR_REF_VECTOR is not implemented in the front end for descriptor-less arrays. The library caf_single has untested support for it.


8.1.5 caf_team_t

Opaque pointer to represent a team-handle. This type is a stand-in for the future implementation of teams. It is about to change without further notice.


8.2 Function ABI Documentation


8.2.1 _gfortran_caf_init — Initialiation function

Description:

This function is called at startup of the program before the Fortran main program, if the latter has been compiled with -fcoarray=lib. It takes as arguments the command-line arguments of the program. It is permitted to pass two NULL pointers as argument; if non-NULL, the library is permitted to modify the arguments.

Syntax:

void _gfortran_caf_init (int *argc, char ***argv)

Arguments:
argcintent(inout) An integer pointer with the number of arguments passed to the program or NULL.
argvintent(inout) A pointer to an array of strings with the command-line arguments or NULL.
NOTES

The function is modelled after the initialization function of the Message Passing Interface (MPI) specification. Due to the way coarray registration works, it might not be the first call to the library. If the main program is not written in Fortran and only a library uses coarrays, it can happen that this function is never called. Therefore, it is recommended that the library does not rely on the passed arguments and whether the call has been done.


8.2.2 _gfortran_caf_finish — Finalization function

Description:

This function is called at the end of the Fortran main program, if it has been compiled with the -fcoarray=lib option.

Syntax:

void _gfortran_caf_finish (void)

NOTES

For non-Fortran programs, it is recommended to call the function at the end of the main program. To ensure that the shutdown is also performed for programs where this function is not explicitly invoked, for instance non-Fortran programs or calls to the system’s exit() function, the library can use a destructor function. Note that programs can also be terminated using the STOP and ERROR STOP statements; those use different library calls.


8.2.3 _gfortran_caf_this_image — Querying the image number

Description:

This function returns the current image number, which is a positive number.

Syntax:

int _gfortran_caf_this_image (int distance)

Arguments:
distanceAs specified for the this_image intrinsic in TS18508. Shall be a non-negative number.
NOTES

If the Fortran intrinsic this_image is invoked without an argument, which is the only permitted form in Fortran 2008, GCC passes 0 as first argument.


8.2.4 _gfortran_caf_num_images — Querying the maximal number of images

Description:

This function returns the number of images in the current team, if distance is 0 or the number of images in the parent team at the specified distance. If failed is -1, the function returns the number of all images at the specified distance; if it is 0, the function returns the number of nonfailed images, and if it is 1, it returns the number of failed images.

Syntax:

int _gfortran_caf_num_images(int distance, int failed)

Arguments:
distancethe distance from this image to the ancestor. Shall be positive.
failedshall be -1, 0, or 1
NOTES

This function follows TS18508. If the num_image intrinsic has no arguments, then the compiler passes distance=0 and failed=-1 to the function.


8.2.5 _gfortran_caf_image_status — Query the status of an image

Description:

Get the status of the image given by the id image of the team given by team. Valid results are zero, for image is ok, STAT_STOPPED_IMAGE from the ISO_FORTRAN_ENV module to indicate that the image has been stopped and STAT_FAILED_IMAGE also from ISO_FORTRAN_ENV to indicate that the image has executed a FAIL IMAGE statement.

Syntax:

int _gfortran_caf_image_status (int image, caf_team_t * team)

Arguments:
imagethe positive scalar id of the image in the current TEAM.
teamoptional; team on the which the inquiry is to be performed.
NOTES

This function follows TS18508. Because team-functionality is not yet implemented a null-pointer is passed for the team argument at the moment.


8.2.6 _gfortran_caf_failed_images — Get an array of the indexes of the failed images

Description:

Get an array of image indexes in the current team that have failed. The array is sorted ascendingly. When team is not provided the current team is to be used. When kind is provided then the resulting array is of that integer kind else it is of default integer kind. The returns an unallocated size zero array when no images have failed.

Syntax:

int _gfortran_caf_failed_images (caf_team_t * team, int * kind)

Arguments:
teamoptional; team on the which the inquiry is to be performed.
imageoptional; the kind of the resulting integer array.
NOTES

This function follows TS18508. Because team-functionality is not yet implemented a null-pointer is passed for the team argument at the moment.


8.2.7 _gfortran_caf_stopped_images — Get an array of the indexes of the stopped images

Description:

Get an array of image indexes in the current team that have stopped. The array is sorted ascendingly. When team is not provided the current team is to be used. When kind is provided then the resulting array is of that integer kind else it is of default integer kind. The returns an unallocated size zero array when no images have failed.

Syntax:

int _gfortran_caf_stopped_images (caf_team_t * team, int * kind)

Arguments:
teamoptional; team on the which the inquiry is to be performed.
imageoptional; the kind of the resulting integer array.
NOTES

This function follows TS18508. Because team-functionality is not yet implemented a null-pointer is passed for the team argument at the moment.


8.2.8 _gfortran_caf_register — Registering coarrays

Description:

Registers memory for a coarray and creates a token to identify the coarray. The routine is called for both coarrays with SAVE attribute and using an explicit ALLOCATE statement. If an error occurs and STAT is a NULL pointer, the function shall abort with printing an error message and starting the error termination. If no error occurs and STAT is present, it shall be set to zero. Otherwise, it shall be set to a positive value and, if not-NULL, ERRMSG shall be set to a string describing the failure. The routine shall register the memory provided in the DATA-component of the array descriptor DESC, when that component is non-NULL, else it shall allocate sufficient memory and provide a pointer to it in the DATA-component of DESC. The array descriptor has rank zero, when a scalar object is to be registered and the array descriptor may be invalid after the call to _gfortran_caf_register. When an array is to be allocated the descriptor persists.

For CAF_REGTYPE_COARRAY_STATIC and CAF_REGTYPE_COARRAY_ALLOC, the passed size is the byte size requested. For CAF_REGTYPE_LOCK_STATIC, CAF_REGTYPE_LOCK_ALLOC and CAF_REGTYPE_CRITICAL it is the array size or one for a scalar.

When CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY is used, then only a token for an allocatable or pointer component is created. The SIZE parameter is not used then. On the contrary when CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY is specified, then the token needs to be registered by a previous call with regtype CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY and either the memory specified in the DESC’s data-ptr is registered or allocate when the data-ptr is NULL.

Syntax:

void caf_register (size_t size, caf_register_t type, caf_token_t *token, gfc_descriptor_t *desc, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
sizeFor normal coarrays, the byte size of the coarray to be allocated; for lock types and event types, the number of elements.
typeone of the caf_register_t types.
tokenintent(out) An opaque pointer identifying the coarray.
descintent(inout) The (pseudo) array descriptor.
statintent(out) For allocatable coarrays, stores the STAT=; may be NULL
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL
errmsg_lenthe buffer size of errmsg.
NOTES

Nonallocatable coarrays have to be registered prior use from remote images. In order to guarantee this, they have to be registered before the main program. This can be achieved by creating constructor functions. That is what GCC does such that also for nonallocatable coarrays the memory is allocated and no static memory is used. The token permits to identify the coarray; to the processor, the token is a nonaliasing pointer. The library can, for instance, store the base address of the coarray in the token, some handle or a more complicated struct. The library may also store the array descriptor DESC when its rank is non-zero.

For lock types, the value shall only be used for checking the allocation status. Note that for critical blocks, the locking is only required on one image; in the locking statement, the processor shall always pass an image index of one for critical-block lock variables (CAF_REGTYPE_CRITICAL). For lock types and critical-block variables, the initial value shall be unlocked (or, respectively, not in critical section) such as the value false; for event types, the initial state should be no event, e.g. zero.


8.2.9 _gfortran_caf_deregister — Deregistering coarrays

Description:

Called to free or deregister the memory of a coarray; the processor calls this function for automatic and explicit deallocation. In case of an error, this function shall fail with an error message, unless the STAT variable is not null. The library is only expected to free memory it allocated itself during a call to _gfortran_caf_register.

Syntax:

void caf_deregister (caf_token_t *token, caf_deregister_t type, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
tokenthe token to free.
typethe type of action to take for the coarray. A CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY is allowed only for allocatable or pointer components of derived type coarrays. The action only deallocates the local memory without deleting the token.
statintent(out) Stores the STAT=; may be NULL
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL
errmsg_lenthe buffer size of errmsg.
NOTES

For nonalloatable coarrays this function is never called. If a cleanup is required, it has to be handled via the finish, stop and error stop functions, and via destructors.


8.2.10 _gfortran_caf_is_present — Query whether an allocatable or pointer component in a derived type coarray is allocated

Description:

Used to query the coarray library whether an allocatable component in a derived type coarray is allocated on a remote image.

Syntax:

void _gfortran_caf_is_present (caf_token_t token, int image_index, gfc_reference_t *ref)

Arguments:
tokenAn opaque pointer identifying the coarray.
image_indexThe ID of the remote image; must be a positive number.
refA chain of references to address the allocatable or pointer component in the derived type coarray. The object reference needs to be a scalar or a full array reference, respectively.

8.2.11 _gfortran_caf_send — Sending data from a local image to a remote image

Description:

Called to send a scalar, an array section or a whole array from a local to a remote image identified by the image_index.

Syntax:

void _gfortran_caf_send (caf_token_t token, size_t offset, int image_index, gfc_descriptor_t *dest, caf_vector_t *dst_vector, gfc_descriptor_t *src, int dst_kind, int src_kind, bool may_require_tmp, int *stat)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number.
destintent(in) Array descriptor for the remote image for the bounds and the size. The base_addr shall not be accessed.
dst_vectorintent(in) If not NULL, it contains the vector subscript of the destination array; the values are relative to the dimension triplet of the dest argument.
srcintent(in) Array descriptor of the local array to be transferred to the remote image
dst_kindintent(in) Kind of the destination argument
src_kindintent(in) Kind of the source argument
may_require_tmpintent(in) The variable is false when it is known at compile time that the dest and src either cannot overlap or overlap (fully or partially) such that walking src and dest in element wise element order (honoring the stride value) will not lead to wrong results. Otherwise, the value is true.
statintent(out) when non-NULL give the result of the operation, i.e., zero on success and non-zero on error. When NULL and an error occurs, then an error message is printed and the program is terminated.
NOTES

It is permitted to have image_index equal the current image; the memory of the send-to and the send-from might (partially) overlap in that case. The implementation has to take care that it handles this case, e.g. using memmove which handles (partially) overlapping memory. If may_require_tmp is true, the library might additionally create a temporary variable, unless additional checks show that this is not required (e.g. because walking backward is possible or because both arrays are contiguous and memmove takes care of overlap issues).

Note that the assignment of a scalar to an array is permitted. In addition, the library has to handle numeric-type conversion and for strings, padding and different character kinds.


8.2.12 _gfortran_caf_get — Getting data from a remote image

Description:

Called to get an array section or a whole array from a remote, image identified by the image_index.

Syntax:

void _gfortran_caf_get (caf_token_t token, size_t offset, int image_index, gfc_descriptor_t *src, caf_vector_t *src_vector, gfc_descriptor_t *dest, int src_kind, int dst_kind, bool may_require_tmp, int *stat)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number.
destintent(out) Array descriptor of the local array to store the data retrieved from the remote image
srcintent(in) Array descriptor for the remote image for the bounds and the size. The base_addr shall not be accessed.
src_vectorintent(in) If not NULL, it contains the vector subscript of the source array; the values are relative to the dimension triplet of the src argument.
dst_kindintent(in) Kind of the destination argument
src_kindintent(in) Kind of the source argument
may_require_tmpintent(in) The variable is false when it is known at compile time that the dest and src either cannot overlap or overlap (fully or partially) such that walking src and dest in element wise element order (honoring the stride value) will not lead to wrong results. Otherwise, the value is true.
statintent(out) When non-NULL give the result of the operation, i.e., zero on success and non-zero on error. When NULL and an error occurs, then an error message is printed and the program is terminated.
NOTES

It is permitted to have image_index equal the current image; the memory of the send-to and the send-from might (partially) overlap in that case. The implementation has to take care that it handles this case, e.g. using memmove which handles (partially) overlapping memory. If may_require_tmp is true, the library might additionally create a temporary variable, unless additional checks show that this is not required (e.g. because walking backward is possible or because both arrays are contiguous and memmove takes care of overlap issues).

Note that the library has to handle numeric-type conversion and for strings, padding and different character kinds.


8.2.13 _gfortran_caf_sendget — Sending data between remote images

Description:

Called to send a scalar, an array section or a whole array from a remote image identified by the src_image_index to a remote image identified by the dst_image_index.

Syntax:

void _gfortran_caf_sendget (caf_token_t dst_token, size_t dst_offset, int dst_image_index, gfc_descriptor_t *dest, caf_vector_t *dst_vector, caf_token_t src_token, size_t src_offset, int src_image_index, gfc_descriptor_t *src, caf_vector_t *src_vector, int dst_kind, int src_kind, bool may_require_tmp, int *stat)

Arguments:
dst_tokenintent(in) An opaque pointer identifying the destination coarray.
dst_offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the destination coarray.
dst_image_indexintent(in) The ID of the destination remote image; must be a positive number.
destintent(in) Array descriptor for the destination remote image for the bounds and the size. The base_addr shall not be accessed.
dst_vectorintent(int) If not NULL, it contains the vector subscript of the destination array; the values are relative to the dimension triplet of the dest argument.
src_tokenintent(in) An opaque pointer identifying the source coarray.
src_offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the source coarray.
src_image_indexintent(in) The ID of the source remote image; must be a positive number.
srcintent(in) Array descriptor of the local array to be transferred to the remote image.
src_vectorintent(in) Array descriptor of the local array to be transferred to the remote image
dst_kindintent(in) Kind of the destination argument
src_kindintent(in) Kind of the source argument
may_require_tmpintent(in) The variable is false when it is known at compile time that the dest and src either cannot overlap or overlap (fully or partially) such that walking src and dest in element wise element order (honoring the stride value) will not lead to wrong results. Otherwise, the value is true.
statintent(out) when non-NULL give the result of the operation, i.e., zero on success and non-zero on error. When NULL and an error occurs, then an error message is printed and the program is terminated.
NOTES

It is permitted to have the same image index for both src_image_index and dst_image_index; the memory of the send-to and the send-from might (partially) overlap in that case. The implementation has to take care that it handles this case, e.g. using memmove which handles (partially) overlapping memory. If may_require_tmp is true, the library might additionally create a temporary variable, unless additional checks show that this is not required (e.g. because walking backward is possible or because both arrays are contiguous and memmove takes care of overlap issues).

Note that the assignment of a scalar to an array is permitted. In addition, the library has to handle numeric-type conversion and for strings, padding and different character kinds.


8.2.14 _gfortran_caf_send_by_ref — Sending data from a local image to a remote image with enhanced referencing options

Description:

Called to send a scalar, an array section or a whole array from a local to a remote image identified by the image_index.

Syntax:

void _gfortran_caf_send_by_ref (caf_token_t token, int image_index, gfc_descriptor_t *src, caf_reference_t *refs, int dst_kind, int src_kind, bool may_require_tmp, bool dst_reallocatable, int *stat, int dst_type)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number.
srcintent(in) Array descriptor of the local array to be transferred to the remote image
refsintent(in) The references on the remote array to store the data given by src. Guaranteed to have at least one entry.
dst_kindintent(in) Kind of the destination argument
src_kindintent(in) Kind of the source argument
may_require_tmpintent(in) The variable is false when it is known at compile time that the dest and src either cannot overlap or overlap (fully or partially) such that walking src and dest in element wise element order (honoring the stride value) will not lead to wrong results. Otherwise, the value is true.
dst_reallocatableintent(in) Set when the destination is of allocatable or pointer type and the refs will allow reallocation, i.e., the ref is a full array or component ref.
statintent(out) When non-NULL give the result of the operation, i.e., zero on success and non-zero on error. When NULL and an error occurs, then an error message is printed and the program is terminated.
dst_typeintent(in) Give the type of the destination. When the destination is not an array, than the precise type, e.g. of a component in a derived type, is not known, but provided here.
NOTES

It is permitted to have image_index equal the current image; the memory of the send-to and the send-from might (partially) overlap in that case. The implementation has to take care that it handles this case, e.g. using memmove which handles (partially) overlapping memory. If may_require_tmp is true, the library might additionally create a temporary variable, unless additional checks show that this is not required (e.g. because walking backward is possible or because both arrays are contiguous and memmove takes care of overlap issues).

Note that the assignment of a scalar to an array is permitted. In addition, the library has to handle numeric-type conversion and for strings, padding and different character kinds.

Because of the more complicated references possible some operations may be unsupported by certain libraries. The library is expected to issue a precise error message why the operation is not permitted.


8.2.15 _gfortran_caf_get_by_ref — Getting data from a remote image using enhanced references

Description:

Called to get a scalar, an array section or a whole array from a remote image identified by the image_index.

Syntax:

void _gfortran_caf_get_by_ref (caf_token_t token, int image_index, caf_reference_t *refs, gfc_descriptor_t *dst, int dst_kind, int src_kind, bool may_require_tmp, bool dst_reallocatable, int *stat, int src_type)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number.
refsintent(in) The references to apply to the remote structure to get the data.
dstintent(in) Array descriptor of the local array to store the data transferred from the remote image. May be reallocated where needed and when DST_REALLOCATABLE allows it.
dst_kindintent(in) Kind of the destination argument
src_kindintent(in) Kind of the source argument
may_require_tmpintent(in) The variable is false when it is known at compile time that the dest and src either cannot overlap or overlap (fully or partially) such that walking src and dest in element wise element order (honoring the stride value) will not lead to wrong results. Otherwise, the value is true.
dst_reallocatableintent(in) Set when DST is of allocatable or pointer type and its refs allow reallocation, i.e., the full array or a component is referenced.
statintent(out) When non-NULL give the result of the operation, i.e., zero on success and non-zero on error. When NULL and an error occurs, then an error message is printed and the program is terminated.
src_typeintent(in) Give the type of the source. When the source is not an array, than the precise type, e.g. of a component in a derived type, is not known, but provided here.
NOTES

It is permitted to have image_index equal the current image; the memory of the send-to and the send-from might (partially) overlap in that case. The implementation has to take care that it handles this case, e.g. using memmove which handles (partially) overlapping memory. If may_require_tmp is true, the library might additionally create a temporary variable, unless additional checks show that this is not required (e.g. because walking backward is possible or because both arrays are contiguous and memmove takes care of overlap issues).

Note that the library has to handle numeric-type conversion and for strings, padding and different character kinds.

Because of the more complicated references possible some operations may be unsupported by certain libraries. The library is expected to issue a precise error message why the operation is not permitted.


8.2.16 _gfortran_caf_sendget_by_ref — Sending data between remote images using enhanced references on both sides

Description:

Called to send a scalar, an array section or a whole array from a remote image identified by the src_image_index to a remote image identified by the dst_image_index.

Syntax:

void _gfortran_caf_sendget_by_ref (caf_token_t dst_token, int dst_image_index, caf_reference_t *dst_refs, caf_token_t src_token, int src_image_index, caf_reference_t *src_refs, int dst_kind, int src_kind, bool may_require_tmp, int *dst_stat, int *src_stat, int dst_type, int src_type)

Arguments:
dst_tokenintent(in) An opaque pointer identifying the destination coarray.
dst_image_indexintent(in) The ID of the destination remote image; must be a positive number.
dst_refsintent(in) The references on the remote array to store the data given by the source. Guaranteed to have at least one entry.
src_tokenintent(in) An opaque pointer identifying the source coarray.
src_image_indexintent(in) The ID of the source remote image; must be a positive number.
src_refsintent(in) The references to apply to the remote structure to get the data.
dst_kindintent(in) Kind of the destination argument
src_kindintent(in) Kind of the source argument
may_require_tmpintent(in) The variable is false when it is known at compile time that the dest and src either cannot overlap or overlap (fully or partially) such that walking src and dest in element wise element order (honoring the stride value) will not lead to wrong results. Otherwise, the value is true.
dst_statintent(out) when non-NULL give the result of the send-operation, i.e., zero on success and non-zero on error. When NULL and an error occurs, then an error message is printed and the program is terminated.
src_statintent(out) When non-NULL give the result of the get-operation, i.e., zero on success and non-zero on error. When NULL and an error occurs, then an error message is printed and the program is terminated.
dst_typeintent(in) Give the type of the destination. When the destination is not an array, than the precise type, e.g. of a component in a derived type, is not known, but provided here.
src_typeintent(in) Give the type of the source. When the source is not an array, than the precise type, e.g. of a component in a derived type, is not known, but provided here.
NOTES

It is permitted to have the same image index for both src_image_index and dst_image_index; the memory of the send-to and the send-from might (partially) overlap in that case. The implementation has to take care that it handles this case, e.g. using memmove which handles (partially) overlapping memory. If may_require_tmp is true, the library might additionally create a temporary variable, unless additional checks show that this is not required (e.g. because walking backward is possible or because both arrays are contiguous and memmove takes care of overlap issues).

Note that the assignment of a scalar to an array is permitted. In addition, the library has to handle numeric-type conversion and for strings, padding and different character kinds.

Because of the more complicated references possible some operations may be unsupported by certain libraries. The library is expected to issue a precise error message why the operation is not permitted.


8.2.17 _gfortran_caf_lock — Locking a lock variable

Description:

Acquire a lock on the given image on a scalar locking variable or for the given array element for an array-valued variable. If the acquired_lock is NULL, the function returns after having obtained the lock. If it is non-NULL, then acquired_lock is assigned the value true (one) when the lock could be obtained and false (zero) otherwise. Locking a lock variable which has already been locked by the same image is an error.

Syntax:

void _gfortran_caf_lock (caf_token_t token, size_t index, int image_index, int *acquired_lock, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
indexintent(in) Array index; first array index is 0. For scalars, it is always 0.
image_indexintent(in) The ID of the remote image; must be a positive number.
acquired_lockintent(out) If not NULL, it returns whether lock could be obtained.
statintent(out) Stores the STAT=; may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg
NOTES

This function is also called for critical blocks; for those, the array index is always zero and the image index is one. Libraries are permitted to use other images for critical-block locking variables.


8.2.18 _gfortran_caf_lock — Unlocking a lock variable

Description:

Release a lock on the given image on a scalar locking variable or for the given array element for an array-valued variable. Unlocking a lock variable which is unlocked or has been locked by a different image is an error.

Syntax:

void _gfortran_caf_unlock (caf_token_t token, size_t index, int image_index, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
indexintent(in) Array index; first array index is 0. For scalars, it is always 0.
image_indexintent(in) The ID of the remote image; must be a positive number.
statintent(out) For allocatable coarrays, stores the STAT=; may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg
NOTES

This function is also called for critical block; for those, the array index is always zero and the image index is one. Libraries are permitted to use other images for critical-block locking variables.


8.2.19 _gfortran_caf_event_post — Post an event

Description:

Increment the event count of the specified event variable.

Syntax:

void _gfortran_caf_event_post (caf_token_t token, size_t index, int image_index, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
indexintent(in) Array index; first array index is 0. For scalars, it is always 0.
image_indexintent(in) The ID of the remote image; must be a positive number; zero indicates the current image, when accessed noncoindexed.
statintent(out) Stores the STAT=; may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg
NOTES

This acts like an atomic add of one to the remote image’s event variable. The statement is an image-control statement but does not imply sync memory. Still, all preceeding push communications of this image to the specified remote image have to be completed before event_wait on the remote image returns.


8.2.20 _gfortran_caf_event_wait — Wait that an event occurred

Description:

Wait until the event count has reached at least the specified until_count; if so, atomically decrement the event variable by this amount and return.

Syntax:

void _gfortran_caf_event_wait (caf_token_t token, size_t index, int until_count, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
indexintent(in) Array index; first array index is 0. For scalars, it is always 0.
until_countintent(in) The number of events which have to be available before the function returns.
statintent(out) Stores the STAT=; may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg
NOTES

This function only operates on a local coarray. It acts like a loop checking atomically the value of the event variable, breaking if the value is greater or equal the requested number of counts. Before the function returns, the event variable has to be decremented by the requested until_count value. A possible implementation would be a busy loop for a certain number of spins (possibly depending on the number of threads relative to the number of available cores) followed by another waiting strategy such as a sleeping wait (possibly with an increasing number of sleep time) or, if possible, a futex wait.

The statement is an image-control statement but does not imply sync memory. Still, all preceeding push communications of this image to the specified remote image have to be completed before event_wait on the remote image returns.


8.2.21 _gfortran_caf_event_query — Query event count

Description:

Return the event count of the specified event variable.

Syntax:

void _gfortran_caf_event_query (caf_token_t token, size_t index, int image_index, int *count, int *stat)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
indexintent(in) Array index; first array index is 0. For scalars, it is always 0.
image_indexintent(in) The ID of the remote image; must be a positive number; zero indicates the current image when accessed noncoindexed.
countintent(out) The number of events currently posted to the event variable.
statintent(out) Stores the STAT=; may be NULL.
NOTES

The typical use is to check the local event variable to only call event_wait when the data is available. However, a coindexed variable is permitted; there is no ordering or synchronization implied. It acts like an atomic fetch of the value of the event variable.


8.2.22 _gfortran_caf_sync_all — All-image barrier

Description:

Synchronization of all images in the current team; the program only continues on a given image after this function has been called on all images of the current team. Additionally, it ensures that all pending data transfers of previous segment have completed.

Syntax:

void _gfortran_caf_sync_all (int *stat, char *errmsg, size_t errmsg_len)

Arguments:
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg

8.2.23 _gfortran_caf_sync_images — Barrier for selected images

Description:

Synchronization between the specified images; the program only continues on a given image after this function has been called on all images specified for that image. Note that one image can wait for all other images in the current team (e.g. via sync images(*)) while those only wait for that specific image. Additionally, sync images ensures that all pending data transfers of previous segments have completed.

Syntax:

void _gfortran_caf_sync_images (int count, int images[], int *stat, char *errmsg, size_t errmsg_len)

Arguments:
countintent(in) The number of images which are provided in the next argument. For a zero-sized array, the value is zero. For sync images (*), the value is -1.
imagesintent(in) An array with the images provided by the user. If count is zero, a NULL pointer is passed.
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg

8.2.24 _gfortran_caf_sync_memory — Wait for completion of segment-memory operations

Description:

Acts as optimization barrier between different segments. It also ensures that all pending memory operations of this image have been completed.

Syntax:

void _gfortran_caf_sync_memory (int *stat, char *errmsg, size_t errmsg_len)

Arguments:
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg
NOTE A simple implementation could be

__asm__ __volatile__ ("":::"memory") to prevent code movements.


8.2.25 _gfortran_caf_error_stop — Error termination with exit code

Description:

Invoked for an ERROR STOP statement which has an integer argument. The function should terminate the program with the specified exit code.

Syntax:

void _gfortran_caf_error_stop (int error)

Arguments:
errorintent(in) The exit status to be used.

8.2.26 _gfortran_caf_error_stop_str — Error termination with string

Description:

Invoked for an ERROR STOP statement which has a string as argument. The function should terminate the program with a nonzero-exit code.

Syntax:

void _gfortran_caf_error_stop (const char *string, size_t len)

Arguments:
stringintent(in) the error message (not zero terminated)
lenintent(in) the length of the string

8.2.27 _gfortran_caf_fail_image — Mark the image failed and end its execution

Description:

Invoked for an FAIL IMAGE statement. The function should terminate the current image.

Syntax:

void _gfortran_caf_fail_image ()

NOTES

This function follows TS18508.


8.2.28 _gfortran_caf_atomic_define — Atomic variable assignment

Description:

Assign atomically a value to an integer or logical variable.

Syntax:

void _gfortran_caf_atomic_define (caf_token_t token, size_t offset, int image_index, void *value, int *stat, int type, int kind)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number; zero indicates the current image when used noncoindexed.
valueintent(in) the value to be assigned, passed by reference
statintent(out) Stores the status STAT= and may be NULL.
typeintent(in) The data type, i.e. BT_INTEGER (1) or BT_LOGICAL (2).
kindintent(in) The kind value (only 4; always int)

8.2.29 _gfortran_caf_atomic_ref — Atomic variable reference

Description:

Reference atomically a value of a kind-4 integer or logical variable.

Syntax:

void _gfortran_caf_atomic_ref (caf_token_t token, size_t offset, int image_index, void *value, int *stat, int type, int kind)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number; zero indicates the current image when used noncoindexed.
valueintent(out) The variable assigned the atomically referenced variable.
statintent(out) Stores the status STAT= and may be NULL.
typethe data type, i.e. BT_INTEGER (1) or BT_LOGICAL (2).
kindThe kind value (only 4; always int)

8.2.30 _gfortran_caf_atomic_cas — Atomic compare and swap

Description:

Atomic compare and swap of a kind-4 integer or logical variable. Assigns atomically the specified value to the atomic variable, if the latter has the value specified by the passed condition value.

Syntax:

void _gfortran_caf_atomic_cas (caf_token_t token, size_t offset, int image_index, void *old, void *compare, void *new_val, int *stat, int type, int kind)

Arguments:
tokenintent(in) An opaque pointer identifying the coarray.
offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number; zero indicates the current image when used noncoindexed.
oldintent(out) The value which the atomic variable had just before the cas operation.
compareintent(in) The value used for comparision.
new_valintent(in) The new value for the atomic variable, assigned to the atomic variable, if compare equals the value of the atomic variable.
statintent(out) Stores the status STAT= and may be NULL.
typeintent(in) the data type, i.e. BT_INTEGER (1) or BT_LOGICAL (2).
kindintent(in) The kind value (only 4; always int)

8.2.31 _gfortran_caf_atomic_op — Atomic operation

Description:

Apply an operation atomically to an atomic integer or logical variable. After the operation, old contains the value just before the operation, which, respectively, adds (GFC_CAF_ATOMIC_ADD) atomically the value to the atomic integer variable or does a bitwise AND, OR or exclusive OR between the atomic variable and value; the result is then stored in the atomic variable.

Syntax:

void _gfortran_caf_atomic_op (int op, caf_token_t token, size_t offset, int image_index, void *value, void *old, int *stat, int type, int kind)

Arguments:
opintent(in) the operation to be performed; possible values GFC_CAF_ATOMIC_ADD (1), GFC_CAF_ATOMIC_AND (2), GFC_CAF_ATOMIC_OR (3), GFC_CAF_ATOMIC_XOR (4).
tokenintent(in) An opaque pointer identifying the coarray.
offsetintent(in) By which amount of bytes the actual data is shifted compared to the base address of the coarray.
image_indexintent(in) The ID of the remote image; must be a positive number; zero indicates the current image when used noncoindexed.
oldintent(out) The value which the atomic variable had just before the atomic operation.
valintent(in) The new value for the atomic variable, assigned to the atomic variable, if compare equals the value of the atomic variable.
statintent(out) Stores the status STAT= and may be NULL.
typeintent(in) the data type, i.e. BT_INTEGER (1) or BT_LOGICAL (2)
kindintent(in) the kind value (only 4; always int)

8.2.32 _gfortran_caf_co_broadcast — Sending data to all images

Description:

Distribute a value from a given image to all other images in the team. Has to be called collectively.

Syntax:

void _gfortran_caf_co_broadcast (gfc_descriptor_t *a, int source_image, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
aintent(inout) An array descriptor with the data to be broadcasted (on source_image) or to be received (other images).
source_imageintent(in) The ID of the image from which the data should be broadcasted.
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg.

8.2.33 _gfortran_caf_co_max — Collective maximum reduction

Description:

Calculates for each array element of the variable a the maximum value for that element in the current team; if result_image has the value 0, the result shall be stored on all images, otherwise, only on the specified image. This function operates on numeric values and character strings.

Syntax:

void _gfortran_caf_co_max (gfc_descriptor_t *a, int result_image, int *stat, char *errmsg, int a_len, size_t errmsg_len)

Arguments:
aintent(inout) An array descriptor for the data to be processed. On the destination image(s) the result overwrites the old content.
result_imageintent(in) The ID of the image to which the reduced value should be copied to; if zero, it has to be copied to all images.
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
a_lenintent(in) the string length of argument a
errmsg_lenintent(in) the buffer size of errmsg
NOTES

If result_image is nonzero, the data in the array descriptor a on all images except of the specified one become undefined; hence, the library may make use of this.


8.2.34 _gfortran_caf_co_min — Collective minimum reduction

Description:

Calculates for each array element of the variable a the minimum value for that element in the current team; if result_image has the value 0, the result shall be stored on all images, otherwise, only on the specified image. This function operates on numeric values and character strings.

Syntax:

void _gfortran_caf_co_min (gfc_descriptor_t *a, int result_image, int *stat, char *errmsg, int a_len, size_t errmsg_len)

Arguments:
aintent(inout) An array descriptor for the data to be processed. On the destination image(s) the result overwrites the old content.
result_imageintent(in) The ID of the image to which the reduced value should be copied to; if zero, it has to be copied to all images.
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
a_lenintent(in) the string length of argument a
errmsg_lenintent(in) the buffer size of errmsg
NOTES

If result_image is nonzero, the data in the array descriptor a on all images except of the specified one become undefined; hence, the library may make use of this.


8.2.35 _gfortran_caf_co_sum — Collective summing reduction

Description:

Calculates for each array element of the variable a the sum of all values for that element in the current team; if result_image has the value 0, the result shall be stored on all images, otherwise, only on the specified image. This function operates on numeric values only.

Syntax:

void _gfortran_caf_co_sum (gfc_descriptor_t *a, int result_image, int *stat, char *errmsg, size_t errmsg_len)

Arguments:
aintent(inout) An array descriptor with the data to be processed. On the destination image(s) the result overwrites the old content.
result_imageintent(in) The ID of the image to which the reduced value should be copied to; if zero, it has to be copied to all images.
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
errmsg_lenintent(in) the buffer size of errmsg
NOTES

If result_image is nonzero, the data in the array descriptor a on all images except of the specified one become undefined; hence, the library may make use of this.


8.2.36 _gfortran_caf_co_reduce — Generic collective reduction

Description:

Calculates for each array element of the variable a the reduction value for that element in the current team; if result_image has the value 0, the result shall be stored on all images, otherwise, only on the specified image. The opr is a pure function doing a mathematically commutative and associative operation.

The opr_flags denote the following; the values are bitwise ored. GFC_CAF_BYREF (1) if the result should be returned by reference; GFC_CAF_HIDDENLEN (2) whether the result and argument string lengths shall be specified as hidden arguments; GFC_CAF_ARG_VALUE (4) whether the arguments shall be passed by value, GFC_CAF_ARG_DESC (8) whether the arguments shall be passed by descriptor.

Syntax:

void _gfortran_caf_co_reduce (gfc_descriptor_t *a, void * (*opr) (void *, void *), int opr_flags, int result_image, int *stat, char *errmsg, int a_len, size_t errmsg_len)

Arguments:
aintent(inout) An array descriptor with the data to be processed. On the destination image(s) the result overwrites the old content.
oprintent(in) Function pointer to the reduction function
opr_flagsintent(in) Flags regarding the reduction function
result_imageintent(in) The ID of the image to which the reduced value should be copied to; if zero, it has to be copied to all images.
statintent(out) Stores the status STAT= and may be NULL.
errmsgintent(out) When an error occurs, this will be set to an error message; may be NULL.
a_lenintent(in) the string length of argument a
errmsg_lenintent(in) the buffer size of errmsg
NOTES

If result_image is nonzero, the data in the array descriptor a on all images except of the specified one become undefined; hence, the library may make use of this.

For character arguments, the result is passed as first argument, followed by the result string length, next come the two string arguments, followed by the two hidden string length arguments. With C binding, there are no hidden arguments and by-reference passing and either only a single character is passed or an array descriptor.


9 Intrinsic Procedures


9.1 Introduction to intrinsic procedures

The intrinsic procedures provided by GNU Fortran include all of the intrinsic procedures required by the Fortran 95 standard, a set of intrinsic procedures for backwards compatibility with G77, and a selection of intrinsic procedures from the Fortran 2003 and Fortran 2008 standards. Any conflict between a description here and a description in either the Fortran 95 standard, the Fortran 2003 standard or the Fortran 2008 standard is unintentional, and the standard(s) should be considered authoritative.

The enumeration of the KIND type parameter is processor defined in the Fortran 95 standard. GNU Fortran defines the default integer type and default real type by INTEGER(KIND=4) and REAL(KIND=4), respectively. The standard mandates that both data types shall have another kind, which have more precision. On typical target architectures supported by gfortran, this kind type parameter is KIND=8. Hence, REAL(KIND=8) and DOUBLE PRECISION are equivalent. In the description of generic intrinsic procedures, the kind type parameter will be specified by KIND=*, and in the description of specific names for an intrinsic procedure the kind type parameter will be explicitly given (e.g., REAL(KIND=4) or REAL(KIND=8)). Finally, for brevity the optional KIND= syntax will be omitted.

Many of the intrinsic procedures take one or more optional arguments. This document follows the convention used in the Fortran 95 standard, and denotes such arguments by square brackets.

GNU Fortran offers the -std=f95 and -std=gnu options, which can be used to restrict the set of intrinsic procedures to a given standard. By default, gfortran sets the -std=gnu option, and so all intrinsic procedures described here are accepted. There is one caveat. For a select group of intrinsic procedures, g77 implemented both a function and a subroutine. Both classes have been implemented in gfortran for backwards compatibility with g77. It is noted here that these functions and subroutines cannot be intermixed in a given subprogram. In the descriptions that follow, the applicable standard for each intrinsic procedure is noted.


9.2 ABORT — Abort the program

Description:

ABORT causes immediate termination of the program. On operating systems that support a core dump, ABORT will produce a core dump. It will also print a backtrace, unless -fno-backtrace is given.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL ABORT

Return value:

Does not return.

Example:
program test_abort
  integer :: i = 1, j = 2
  if (i /= j) call abort
end program test_abort
See also:

EXIT — Exit the program with status., KILL — Send a signal to a process, BACKTRACE — Show a backtrace


9.3 ABS — Absolute value

Description:

ABS(A) computes the absolute value of A.

Standard:

Fortran 77 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = ABS(A)

Arguments:
AThe type of the argument shall be an INTEGER, REAL, or COMPLEX.
Return value:

The return value is of the same type and kind as the argument except the return value is REAL for a COMPLEX argument.

Example:
program test_abs
  integer :: i = -1
  real :: x = -1.e0
  complex :: z = (-1.e0,0.e0)
  i = abs(i)
  x = abs(x)
  x = abs(z)
end program test_abs
Specific names:
NameArgumentReturn typeStandard
ABS(A)REAL(4) AREAL(4)Fortran 77 and later
CABS(A)COMPLEX(4) AREAL(4)Fortran 77 and later
DABS(A)REAL(8) AREAL(8)Fortran 77 and later
IABS(A)INTEGER(4) AINTEGER(4)Fortran 77 and later
BABS(A)INTEGER(1) AINTEGER(1)GNU extension
IIABS(A)INTEGER(2) AINTEGER(2)GNU extension
JIABS(A)INTEGER(4) AINTEGER(4)GNU extension
KIABS(A)INTEGER(8) AINTEGER(8)GNU extension
ZABS(A)COMPLEX(8) AREAL(8)GNU extension
CDABS(A)COMPLEX(8) AREAL(8)GNU extension

9.4 ACCESS — Checks file access modes

Description:

ACCESS(NAME, MODE) checks whether the file NAME exists, is readable, writable or executable. Except for the executable check, ACCESS can be replaced by Fortran 95’s INQUIRE.

Standard:

GNU extension

Class:

Inquiry function

Syntax:

RESULT = ACCESS(NAME, MODE)

Arguments:
NAMEScalar CHARACTER of default kind with the file name. Tailing blank are ignored unless the character achar(0) is present, then all characters up to and excluding achar(0) are used as file name.
MODEScalar CHARACTER of default kind with the file access mode, may be any concatenation of "r" (readable), "w" (writable) and "x" (executable), or " " to check for existence.
Return value:

Returns a scalar INTEGER, which is 0 if the file is accessible in the given mode; otherwise or if an invalid argument has been given for MODE the value 1 is returned.

Example:
program access_test
  implicit none
  character(len=*), parameter :: file  = 'test.dat'
  character(len=*), parameter :: file2 = 'test.dat  '//achar(0)
  if(access(file,' ') == 0) print *, trim(file),' is exists'
  if(access(file,'r') == 0) print *, trim(file),' is readable'
  if(access(file,'w') == 0) print *, trim(file),' is writable'
  if(access(file,'x') == 0) print *, trim(file),' is executable'
  if(access(file2,'rwx') == 0) &
    print *, trim(file2),' is readable, writable and executable'
end program access_test

9.5 ACHAR — Character in ASCII collating sequence

Description:

ACHAR(I) returns the character located at position I in the ASCII collating sequence.

Standard:

Fortran 77 and later, with KIND argument Fortran 2003 and later

Class:

Elemental function

Syntax:

RESULT = ACHAR(I [, KIND])

Arguments:
IThe type shall be INTEGER.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type CHARACTER with a length of one. If the KIND argument is present, the return value is of the specified kind and of the default kind otherwise.

Example:
program test_achar
  character c
  c = achar(32)
end program test_achar
Note:

See ICHAR — Character-to-integer conversion function for a discussion of converting between numerical values and formatted string representations.

See also:

CHAR — Character conversion function, IACHAR — Code in ASCII collating sequence, ICHAR — Character-to-integer conversion function


9.6 ACOS — Arccosine function

Description:

ACOS(X) computes the arccosine of X (inverse of COS(X)).

Standard:

Fortran 77 and later, for a complex argument Fortran 2008 or later

Class:

Elemental function

Syntax:

RESULT = ACOS(X)

Arguments:
XThe type shall either be REAL with a magnitude that is less than or equal to one - or the type shall be COMPLEX.
Return value:

The return value is of the same type and kind as X. The real part of the result is in radians and lies in the range 0 \leq \Re \acos(x) \leq \pi.

Example:
program test_acos
  real(8) :: x = 0.866_8
  x = acos(x)
end program test_acos
Specific names:
NameArgumentReturn typeStandard
ACOS(X)REAL(4) XREAL(4)Fortran 77 and later
DACOS(X)REAL(8) XREAL(8)Fortran 77 and later
See also:

Inverse function: COS — Cosine function Degrees function: ACOSD — Arccosine function, degrees


9.7 ACOSD — Arccosine function, degrees

Description:

ACOSD(X) computes the arccosine of X in degrees (inverse of COSD(X)).

This function is for compatibility only and should be avoided in favor of standard constructs wherever possible.

Standard:

GNU extension, enabled with -fdec-math

Class:

Elemental function

Syntax:

RESULT = ACOSD(X)

Arguments:
XThe type shall either be REAL with a magnitude that is less than or equal to one - or the type shall be COMPLEX.
Return value:

The return value is of the same type and kind as X. The real part of the result is in degrees and lies in the range 0 \leq \Re \acos(x) \leq 180.

Example:
program test_acosd
  real(8) :: x = 0.866_8
  x = acosd(x)
end program test_acosd
Specific names:
NameArgumentReturn typeStandard
ACOSD(X)REAL(4) XREAL(4)GNU extension
DACOSD(X)REAL(8) XREAL(8)GNU extension
See also:

Inverse function: COSD — Cosine function, degrees Radians function: ACOS — Arccosine function


9.8 ACOSH — Inverse hyperbolic cosine function

Description:

ACOSH(X) computes the inverse hyperbolic cosine of X.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = ACOSH(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value has the same type and kind as X. If X is complex, the imaginary part of the result is in radians and lies between 0 \leq \Im \acosh(x) \leq \pi.

Example:
PROGRAM test_acosh
  REAL(8), DIMENSION(3) :: x = (/ 1.0, 2.0, 3.0 /)
  WRITE (*,*) ACOSH(x)
END PROGRAM
Specific names:
NameArgumentReturn typeStandard
DACOSH(X)REAL(8) XREAL(8)GNU extension
See also:

Inverse function: COSH — Hyperbolic cosine function


9.9 ADJUSTL — Left adjust a string

Description:

ADJUSTL(STRING) will left adjust a string by removing leading spaces. Spaces are inserted at the end of the string as needed.

Standard:

Fortran 90 and later

Class:

Elemental function

Syntax:

RESULT = ADJUSTL(STRING)

Arguments:
STRINGThe type shall be CHARACTER.
Return value:

The return value is of type CHARACTER and of the same kind as STRING where leading spaces are removed and the same number of spaces are inserted on the end of STRING.

Example:
program test_adjustl
  character(len=20) :: str = '   gfortran'
  str = adjustl(str)
  print *, str
end program test_adjustl
See also:

ADJUSTR — Right adjust a string, TRIM — Remove trailing blank characters of a string


9.10 ADJUSTR — Right adjust a string

Description:

ADJUSTR(STRING) will right adjust a string by removing trailing spaces. Spaces are inserted at the start of the string as needed.

Standard:

Fortran 90 and later

Class:

Elemental function

Syntax:

RESULT = ADJUSTR(STRING)

Arguments:
STRThe type shall be CHARACTER.
Return value:

The return value is of type CHARACTER and of the same kind as STRING where trailing spaces are removed and the same number of spaces are inserted at the start of STRING.

Example:
program test_adjustr
  character(len=20) :: str = 'gfortran'
  str = adjustr(str)
  print *, str
end program test_adjustr
See also:

ADJUSTL — Left adjust a string, TRIM — Remove trailing blank characters of a string


9.11 AIMAG — Imaginary part of complex number

Description:

AIMAG(Z) yields the imaginary part of complex argument Z. The IMAG(Z) and IMAGPART(Z) intrinsic functions are provided for compatibility with g77, and their use in new code is strongly discouraged.

Standard:

Fortran 77 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = AIMAG(Z)

Arguments:
ZThe type of the argument shall be COMPLEX.
Return value:

The return value is of type REAL with the kind type parameter of the argument.

Example:
program test_aimag
  complex(4) z4
  complex(8) z8
  z4 = cmplx(1.e0_4, 0.e0_4)
  z8 = cmplx(0.e0_8, 1.e0_8)
  print *, aimag(z4), dimag(z8)
end program test_aimag
Specific names:
NameArgumentReturn typeStandard
AIMAG(Z)COMPLEX ZREALFortran 77 and later
DIMAG(Z)COMPLEX(8) ZREAL(8)GNU extension
IMAG(Z)COMPLEX ZREALGNU extension
IMAGPART(Z)COMPLEX ZREALGNU extension

9.12 AINT — Truncate to a whole number

Description:

AINT(A [, KIND]) truncates its argument to a whole number.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = AINT(A [, KIND])

Arguments:
AThe type of the argument shall be REAL.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type REAL with the kind type parameter of the argument if the optional KIND is absent; otherwise, the kind type parameter will be given by KIND. If the magnitude of X is less than one, AINT(X) returns zero. If the magnitude is equal to or greater than one then it returns the largest whole number that does not exceed its magnitude. The sign is the same as the sign of X.

Example:
program test_aint
  real(4) x4
  real(8) x8
  x4 = 1.234E0_4
  x8 = 4.321_8
  print *, aint(x4), dint(x8)
  x8 = aint(x4,8)
end program test_aint
Specific names:
NameArgumentReturn typeStandard
AINT(A)REAL(4) AREAL(4)Fortran 77 and later
DINT(A)REAL(8) AREAL(8)Fortran 77 and later

9.13 ALARM — Execute a routine after a given delay

Description:

ALARM(SECONDS, HANDLER [, STATUS]) causes external subroutine HANDLER to be executed after a delay of SECONDS by using alarm(2) to set up a signal and signal(2) to catch it. If STATUS is supplied, it will be returned with the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL ALARM(SECONDS, HANDLER [, STATUS])

Arguments:
SECONDSThe type of the argument shall be a scalar INTEGER. It is INTENT(IN).
HANDLERSignal handler (INTEGER FUNCTION or SUBROUTINE) or dummy/global INTEGER scalar. The scalar values may be either SIG_IGN=1 to ignore the alarm generated or SIG_DFL=0 to set the default action. It is INTENT(IN).
STATUS(Optional) STATUS shall be a scalar variable of the default INTEGER kind. It is INTENT(OUT).
Example:
program test_alarm
  external handler_print
  integer i
  call alarm (3, handler_print, i)
  print *, i
  call sleep(10)
end program test_alarm

This will cause the external routine handler_print to be called after 3 seconds.


9.14 ALL — All values in MASK along DIM are true

Description:

ALL(MASK [, DIM]) determines if all the values are true in MASK in the array along dimension DIM.

Standard:

Fortran 90 and later

Class:

Transformational function

Syntax:

RESULT = ALL(MASK [, DIM])

Arguments:
MASKThe type of the argument shall be LOGICAL and it shall not be scalar.
DIM(Optional) DIM shall be a scalar integer with a value that lies between one and the rank of MASK.
Return value:

ALL(MASK) returns a scalar value of type LOGICAL where the kind type parameter is the same as the kind type parameter of MASK. If DIM is present, then ALL(MASK, DIM) returns an array with the rank of MASK minus 1. The shape is determined from the shape of MASK where the DIM dimension is elided.

(A)

ALL(MASK) is true if all elements of MASK are true. It also is true if MASK has zero size; otherwise, it is false.

(B)

If the rank of MASK is one, then ALL(MASK,DIM) is equivalent to ALL(MASK). If the rank is greater than one, then ALL(MASK,DIM) is determined by applying ALL to the array sections.

Example:
program test_all
  logical l
  l = all((/.true., .true., .true./))
  print *, l
  call section
  contains
    subroutine section
      integer a(2,3), b(2,3)
      a = 1
      b = 1
      b(2,2) = 2
      print *, all(a .eq. b, 1)
      print *, all(a .eq. b, 2)
    end subroutine section
end program test_all

9.15 ALLOCATED — Status of an allocatable entity

Description:

ALLOCATED(ARRAY) and ALLOCATED(SCALAR) check the allocation status of ARRAY and SCALAR, respectively.

Standard:

Fortran 90 and later. Note, the SCALAR= keyword and allocatable scalar entities are available in Fortran 2003 and later.

Class:

Inquiry function

Syntax:
RESULT = ALLOCATED(ARRAY)
RESULT = ALLOCATED(SCALAR)
Arguments:
ARRAYThe argument shall be an ALLOCATABLE array.
SCALARThe argument shall be an ALLOCATABLE scalar.
Return value:

The return value is a scalar LOGICAL with the default logical kind type parameter. If the argument is allocated, then the result is .TRUE.; otherwise, it returns .FALSE.

Example:
program test_allocated
  integer :: i = 4
  real(4), allocatable :: x(:)
  if (.not. allocated(x)) allocate(x(i))
end program test_allocated

9.16 AND — Bitwise logical AND

Description:

Bitwise logical AND.

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. For integer arguments, programmers should consider the use of the IAND — Bitwise logical and intrinsic defined by the Fortran standard.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = AND(I, J)

Arguments:
IThe type shall be either a scalar INTEGER type or a scalar LOGICAL type or a boz-literal-constant.
JThe type shall be the same as the type of I or a boz-literal-constant. I and J shall not both be boz-literal-constants. If either I or J is a boz-literal-constant, then the other argument must be a scalar INTEGER.
Return value:

The return type is either a scalar INTEGER or a scalar LOGICAL. If the kind type parameters differ, then the smaller kind type is implicitly converted to larger kind, and the return has the larger kind. A boz-literal-constant is converted to an INTEGER with the kind type parameter of the other argument as-if a call to INT — Convert to integer type occurred.

Example:
PROGRAM test_and
  LOGICAL :: T = .TRUE., F = .FALSE.
  INTEGER :: a, b
  DATA a / Z'F' /, b / Z'3' /

  WRITE (*,*) AND(T, T), AND(T, F), AND(F, T), AND(F, F)
  WRITE (*,*) AND(a, b)
END PROGRAM
See also:

Fortran 95 elemental function: IAND — Bitwise logical and


9.17 ANINT — Nearest whole number

Description:

ANINT(A [, KIND]) rounds its argument to the nearest whole number.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = ANINT(A [, KIND])

Arguments:
AThe type of the argument shall be REAL.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type real with the kind type parameter of the argument if the optional KIND is absent; otherwise, the kind type parameter will be given by KIND. If A is greater than zero, ANINT(A) returns AINT(X+0.5). If A is less than or equal to zero then it returns AINT(X-0.5).

Example:
program test_anint
  real(4) x4
  real(8) x8
  x4 = 1.234E0_4
  x8 = 4.321_8
  print *, anint(x4), dnint(x8)
  x8 = anint(x4,8)
end program test_anint
Specific names:
NameArgumentReturn typeStandard
ANINT(A)REAL(4) AREAL(4)Fortran 77 and later
DNINT(A)REAL(8) AREAL(8)Fortran 77 and later

9.18 ANY — Any value in MASK along DIM is true

Description:

ANY(MASK [, DIM]) determines if any of the values in the logical array MASK along dimension DIM are .TRUE..

Standard:

Fortran 90 and later

Class:

Transformational function

Syntax:

RESULT = ANY(MASK [, DIM])

Arguments:
MASKThe type of the argument shall be LOGICAL and it shall not be scalar.
DIM(Optional) DIM shall be a scalar integer with a value that lies between one and the rank of MASK.
Return value:

ANY(MASK) returns a scalar value of type LOGICAL where the kind type parameter is the same as the kind type parameter of MASK. If DIM is present, then ANY(MASK, DIM) returns an array with the rank of MASK minus 1. The shape is determined from the shape of MASK where the DIM dimension is elided.

(A)

ANY(MASK) is true if any element of MASK is true; otherwise, it is false. It also is false if MASK has zero size.

(B)

If the rank of MASK is one, then ANY(MASK,DIM) is equivalent to ANY(MASK). If the rank is greater than one, then ANY(MASK,DIM) is determined by applying ANY to the array sections.

Example:
program test_any
  logical l
  l = any((/.true., .true., .true./))
  print *, l
  call section
  contains
    subroutine section
      integer a(2,3), b(2,3)
      a = 1
      b = 1
      b(2,2) = 2
      print *, any(a .eq. b, 1)
      print *, any(a .eq. b, 2)
    end subroutine section
end program test_any

9.19 ASIN — Arcsine function

Description:

ASIN(X) computes the arcsine of its X (inverse of SIN(X)).

Standard:

Fortran 77 and later, for a complex argument Fortran 2008 or later

Class:

Elemental function

Syntax:

RESULT = ASIN(X)

Arguments:
XThe type shall be either REAL and a magnitude that is less than or equal to one - or be COMPLEX.
Return value:

The return value is of the same type and kind as X. The real part of the result is in radians and lies in the range -\pi/2 \leq \Re \asin(x) \leq \pi/2.

Example:
program test_asin
  real(8) :: x = 0.866_8
  x = asin(x)
end program test_asin
Specific names:
NameArgumentReturn typeStandard
ASIN(X)REAL(4) XREAL(4)Fortran 77 and later
DASIN(X)REAL(8) XREAL(8)Fortran 77 and later
See also:

Inverse function: SIN — Sine function Degrees function: ASIND — Arcsine function, degrees


9.20 ASIND — Arcsine function, degrees

Description:

ASIND(X) computes the arcsine of its X in degrees (inverse of SIND(X)).

This function is for compatibility only and should be avoided in favor of standard constructs wherever possible.

Standard:

GNU extension, enabled with -fdec-math.

Class:

Elemental function

Syntax:

RESULT = ASIND(X)

Arguments:
XThe type shall be either REAL and a magnitude that is less than or equal to one - or be COMPLEX.
Return value:

The return value is of the same type and kind as X. The real part of the result is in degrees and lies in the range -90 \leq \Re \asin(x) \leq 90.

Example:
program test_asind
  real(8) :: x = 0.866_8
  x = asind(x)
end program test_asind
Specific names:
NameArgumentReturn typeStandard
ASIND(X)REAL(4) XREAL(4)GNU extension
DASIND(X)REAL(8) XREAL(8)GNU extension
See also:

Inverse function: SIND — Sine function, degrees Radians function: ASIN — Arcsine function


9.21 ASINH — Inverse hyperbolic sine function

Description:

ASINH(X) computes the inverse hyperbolic sine of X.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = ASINH(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value is of the same type and kind as X. If X is complex, the imaginary part of the result is in radians and lies between -\pi/2 \leq \Im \asinh(x) \leq \pi/2.

Example:
PROGRAM test_asinh
  REAL(8), DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /)
  WRITE (*,*) ASINH(x)
END PROGRAM
Specific names:
NameArgumentReturn typeStandard
DASINH(X)REAL(8) XREAL(8)GNU extension.
See also:

Inverse function: SINH — Hyperbolic sine function


9.22 ASSOCIATED — Status of a pointer or pointer/target pair

Description:

ASSOCIATED(POINTER [, TARGET]) determines the status of the pointer POINTER or if POINTER is associated with the target TARGET.

Standard:

Fortran 90 and later

Class:

Inquiry function

Syntax:

RESULT = ASSOCIATED(POINTER [, TARGET])

Arguments:
POINTERPOINTER shall have the POINTER attribute and it can be of any type.
TARGET(Optional) TARGET shall be a pointer or a target. It must have the same type, kind type parameter, and array rank as POINTER.

The association status of neither POINTER nor TARGET shall be undefined.

Return value:

ASSOCIATED(POINTER) returns a scalar value of type LOGICAL(4). There are several cases:

(A) When the optional TARGET is not present then

ASSOCIATED(POINTER) is true if POINTER is associated with a target; otherwise, it returns false.

(B) If TARGET is present and a scalar target, the result is true if

TARGET is not a zero-sized storage sequence and the target associated with POINTER occupies the same storage units. If POINTER is disassociated, the result is false.

(C) If TARGET is present and an array target, the result is true if

TARGET and POINTER have the same shape, are not zero-sized arrays, are arrays whose elements are not zero-sized storage sequences, and TARGET and POINTER occupy the same storage units in array element order. As in case(B), the result is false, if POINTER is disassociated.

(D) If TARGET is present and an scalar pointer, the result is true

if TARGET is associated with POINTER, the target associated with TARGET are not zero-sized storage sequences and occupy the same storage units. The result is false, if either TARGET or POINTER is disassociated.

(E) If TARGET is present and an array pointer, the result is true if

target associated with POINTER and the target associated with TARGET have the same shape, are not zero-sized arrays, are arrays whose elements are not zero-sized storage sequences, and TARGET and POINTER occupy the same storage units in array element order. The result is false, if either TARGET or POINTER is disassociated.

Example:
program test_associated
   implicit none
   real, target  :: tgt(2) = (/1., 2./)
   real, pointer :: ptr(:)
   ptr => tgt
   if (associated(ptr)     .eqv. .false.) call abort
   if (associated(ptr,tgt) .eqv. .false.) call abort
end program test_associated
See also:

NULL — Function that returns an disassociated pointer


9.23 ATAN — Arctangent function

Description:

ATAN(X) computes the arctangent of X.

Standard:

Fortran 77 and later, for a complex argument and for two arguments Fortran 2008 or later

Class:

Elemental function

Syntax:
RESULT = ATAN(X)
RESULT = ATAN(Y, X)
Arguments:
XThe type shall be REAL or COMPLEX; if Y is present, X shall be REAL.
YThe type and kind type parameter shall be the same as X.
Return value:

The return value is of the same type and kind as X. If Y is present, the result is identical to ATAN2(Y,X). Otherwise, it the arcus tangent of X, where the real part of the result is in radians and lies in the range -\pi/2 \leq \Re \atan(x) \leq \pi/2.

Example:
program test_atan
  real(8) :: x = 2.866_8
  x = atan(x)
end program test_atan
Specific names:
NameArgumentReturn typeStandard
ATAN(X)REAL(4) XREAL(4)Fortran 77 and later
DATAN(X)REAL(8) XREAL(8)Fortran 77 and later
See also:

Inverse function: TAN — Tangent function Degrees function: ATAND — Arctangent function, degrees


9.24 ATAND — Arctangent function, degrees

Description:

ATAND(X) computes the arctangent of X in degrees (inverse of TAND — Tangent function, degrees).

This function is for compatibility only and should be avoided in favor of standard constructs wherever possible.

Standard:

GNU extension, enabled with -fdec-math.

Class:

Elemental function

Syntax:
RESULT = ATAND(X)
RESULT = ATAND(Y, X)
Arguments:
XThe type shall be REAL or COMPLEX; if Y is present, X shall be REAL.
YThe type and kind type parameter shall be the same as X.
Return value:

The return value is of the same type and kind as X. If Y is present, the result is identical to ATAND2(Y,X). Otherwise, it is the arcus tangent of X, where the real part of the result is in degrees and lies in the range -90 \leq \Re \atand(x) \leq 90.

Example:
program test_atand
  real(8) :: x = 2.866_8
  x = atand(x)
end program test_atand
Specific names:
NameArgumentReturn typeStandard
ATAND(X)REAL(4) XREAL(4)GNU extension
DATAND(X)REAL(8) XREAL(8)GNU extension
See also:

Inverse function: TAND — Tangent function, degrees Radians function: ATAN — Arctangent function


9.25 ATAN2 — Arctangent function

Description:

ATAN2(Y, X) computes the principal value of the argument function of the complex number X + i Y. This function can be used to transform from Cartesian into polar coordinates and allows to determine the angle in the correct quadrant.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = ATAN2(Y, X)

Arguments:
YThe type shall be REAL.
XThe type and kind type parameter shall be the same as Y. If Y is zero, then X must be nonzero.
Return value:

The return value has the same type and kind type parameter as Y. It is the principal value of the complex number X + i Y. If X is nonzero, then it lies in the range -\pi \le \atan (x) \leq \pi. The sign is positive if Y is positive. If Y is zero, then the return value is zero if X is strictly positive, \pi if X is negative and Y is positive zero (or the processor does not handle signed zeros), and -\pi if X is negative and Y is negative zero. Finally, if X is zero, then the magnitude of the result is \pi/2.

Example:
program test_atan2
  real(4) :: x = 1.e0_4, y = 0.5e0_4
  x = atan2(y,x)
end program test_atan2
Specific names:
NameArgumentReturn typeStandard
ATAN2(X, Y)REAL(4) X, YREAL(4)Fortran 77 and later
DATAN2(X, Y)REAL(8) X, YREAL(8)Fortran 77 and later
See also:

Alias: ATAN — Arctangent function Degrees function: ATAN2D — Arctangent function, degrees


9.26 ATAN2D — Arctangent function, degrees

Description:

ATAN2D(Y, X) computes the principal value of the argument function of the complex number X + i Y in degrees. This function can be used to transform from Cartesian into polar coordinates and allows to determine the angle in the correct quadrant.

This function is for compatibility only and should be avoided in favor of standard constructs wherever possible.

Standard:

GNU extension, enabled with -fdec-math.

Class:

Elemental function

Syntax:

RESULT = ATAN2D(Y, X)

Arguments:
YThe type shall be REAL.
XThe type and kind type parameter shall be the same as Y. If Y is zero, then X must be nonzero.
Return value:

The return value has the same type and kind type parameter as Y. It is the principal value of the complex number X + i Y. If X is nonzero, then it lies in the range -180 \le \atan (x) \leq 180. The sign is positive if Y is positive. If Y is zero, then the return value is zero if X is strictly positive, 180 if X is negative and Y is positive zero (or the processor does not handle signed zeros), and -180 if X is negative and Y is negative zero. Finally, if X is zero, then the magnitude of the result is 90.

Example:
program test_atan2d
  real(4) :: x = 1.e0_4, y = 0.5e0_4
  x = atan2d(y,x)
end program test_atan2d
Specific names:
NameArgumentReturn typeStandard
ATAN2D(X, Y)REAL(4) X, YREAL(4)GNU extension
DATAN2D(X, Y)REAL(8) X, YREAL(8)GNU extension
See also:

Alias: ATAND — Arctangent function, degrees Radians function: ATAN2 — Arctangent function


9.27 ATANH — Inverse hyperbolic tangent function

Description:

ATANH(X) computes the inverse hyperbolic tangent of X.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = ATANH(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value has same type and kind as X. If X is complex, the imaginary part of the result is in radians and lies between -\pi/2 \leq \Im \atanh(x) \leq \pi/2.

Example:
PROGRAM test_atanh
  REAL, DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /)
  WRITE (*,*) ATANH(x)
END PROGRAM
Specific names:
NameArgumentReturn typeStandard
DATANH(X)REAL(8) XREAL(8)GNU extension
See also:

Inverse function: TANH — Hyperbolic tangent function


9.28 ATOMIC_ADD — Atomic ADD operation

Description:

ATOMIC_ADD(ATOM, VALUE) atomically adds the value of VALUE to the variable ATOM. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_ADD (ATOM, VALUE [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*]
  call atomic_add (atom[1], this_image())
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_FETCH_ADD — Atomic ADD operation with prior fetch, ISO_FORTRAN_ENV, ATOMIC_AND — Atomic bitwise AND operation, ATOMIC_OR — Atomic bitwise OR operation, ATOMIC_XOR — Atomic bitwise OR operation


9.29 ATOMIC_AND — Atomic bitwise AND operation

Description:

ATOMIC_AND(ATOM, VALUE) atomically defines ATOM with the bitwise AND between the values of ATOM and VALUE. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_AND (ATOM, VALUE [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*]
  call atomic_and (atom[1], int(b'10100011101'))
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_FETCH_AND — Atomic bitwise AND operation with prior fetch, ISO_FORTRAN_ENV, ATOMIC_ADD — Atomic ADD operation, ATOMIC_OR — Atomic bitwise OR operation, ATOMIC_XOR — Atomic bitwise OR operation


9.30 ATOMIC_CAS — Atomic compare and swap

Description:

ATOMIC_CAS compares the variable ATOM with the value of COMPARE; if the value is the same, ATOM is set to the value of NEW. Additionally, OLD is set to the value of ATOM that was used for the comparison. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_CAS (ATOM, OLD, COMPARE, NEW [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of either integer type with ATOMIC_INT_KIND kind or logical type with ATOMIC_LOGICAL_KIND kind.
OLDScalar of the same type and kind as ATOM.
COMPAREScalar variable of the same type and kind as ATOM.
NEWScalar variable of the same type as ATOM. If kind is different, the value is converted to the kind of ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  logical(atomic_logical_kind) :: atom[*], prev
  call atomic_cas (atom[1], prev, .false., .true.))
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_REF — Obtaining the value of a variable atomically, ISO_FORTRAN_ENV


9.31 ATOMIC_DEFINE — Setting a variable atomically

Description:

ATOMIC_DEFINE(ATOM, VALUE) defines the variable ATOM with the value VALUE atomically. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

Fortran 2008 and later; with STAT, TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_DEFINE (ATOM, VALUE [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of either integer type with ATOMIC_INT_KIND kind or logical type with ATOMIC_LOGICAL_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*]
  call atomic_define (atom[1], this_image())
end program atomic
See also:

ATOMIC_REF — Obtaining the value of a variable atomically, ATOMIC_CAS — Atomic compare and swap, ISO_FORTRAN_ENV, ATOMIC_ADD — Atomic ADD operation, ATOMIC_AND — Atomic bitwise AND operation, ATOMIC_OR — Atomic bitwise OR operation, ATOMIC_XOR — Atomic bitwise OR operation


9.32 ATOMIC_FETCH_ADD — Atomic ADD operation with prior fetch

Description:

ATOMIC_FETCH_ADD(ATOM, VALUE, OLD) atomically stores the value of ATOM in OLD and adds the value of VALUE to the variable ATOM. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_FETCH_ADD (ATOM, VALUE, old [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind. ATOMIC_LOGICAL_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
OLDScalar of the same type and kind as ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*], old
  call atomic_add (atom[1], this_image(), old)
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_ADD — Atomic ADD operation, ISO_FORTRAN_ENV, ATOMIC_FETCH_AND — Atomic bitwise AND operation with prior fetch, ATOMIC_FETCH_OR — Atomic bitwise OR operation with prior fetch, ATOMIC_FETCH_XOR — Atomic bitwise XOR operation with prior fetch


9.33 ATOMIC_FETCH_AND — Atomic bitwise AND operation with prior fetch

Description:

ATOMIC_AND(ATOM, VALUE) atomically stores the value of ATOM in OLD and defines ATOM with the bitwise AND between the values of ATOM and VALUE. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_FETCH_AND (ATOM, VALUE, OLD [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
OLDScalar of the same type and kind as ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*], old
  call atomic_fetch_and (atom[1], int(b'10100011101'), old)
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_AND — Atomic bitwise AND operation, ISO_FORTRAN_ENV, ATOMIC_FETCH_ADD — Atomic ADD operation with prior fetch, ATOMIC_FETCH_OR — Atomic bitwise OR operation with prior fetch, ATOMIC_FETCH_XOR — Atomic bitwise XOR operation with prior fetch


9.34 ATOMIC_FETCH_OR — Atomic bitwise OR operation with prior fetch

Description:

ATOMIC_OR(ATOM, VALUE) atomically stores the value of ATOM in OLD and defines ATOM with the bitwise OR between the values of ATOM and VALUE. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_FETCH_OR (ATOM, VALUE, OLD [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
OLDScalar of the same type and kind as ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*], old
  call atomic_fetch_or (atom[1], int(b'10100011101'), old)
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_OR — Atomic bitwise OR operation, ISO_FORTRAN_ENV, ATOMIC_FETCH_ADD — Atomic ADD operation with prior fetch, ATOMIC_FETCH_AND — Atomic bitwise AND operation with prior fetch, ATOMIC_FETCH_XOR — Atomic bitwise XOR operation with prior fetch


9.35 ATOMIC_FETCH_XOR — Atomic bitwise XOR operation with prior fetch

Description:

ATOMIC_XOR(ATOM, VALUE) atomically stores the value of ATOM in OLD and defines ATOM with the bitwise XOR between the values of ATOM and VALUE. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_FETCH_XOR (ATOM, VALUE, OLD [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
OLDScalar of the same type and kind as ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*], old
  call atomic_fetch_xor (atom[1], int(b'10100011101'), old)
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_XOR — Atomic bitwise OR operation, ISO_FORTRAN_ENV, ATOMIC_FETCH_ADD — Atomic ADD operation with prior fetch, ATOMIC_FETCH_AND — Atomic bitwise AND operation with prior fetch, ATOMIC_FETCH_OR — Atomic bitwise OR operation with prior fetch


9.36 ATOMIC_OR — Atomic bitwise OR operation

Description:

ATOMIC_OR(ATOM, VALUE) atomically defines ATOM with the bitwise AND between the values of ATOM and VALUE. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_OR (ATOM, VALUE [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*]
  call atomic_or (atom[1], int(b'10100011101'))
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_FETCH_OR — Atomic bitwise OR operation with prior fetch, ISO_FORTRAN_ENV, ATOMIC_ADD — Atomic ADD operation, ATOMIC_OR — Atomic bitwise OR operation, ATOMIC_XOR — Atomic bitwise OR operation


9.37 ATOMIC_REF — Obtaining the value of a variable atomically

Description:

ATOMIC_DEFINE(ATOM, VALUE) atomically assigns the value of the variable ATOM to VALUE. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

Fortran 2008 and later; with STAT, TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_REF(VALUE, ATOM [, STAT])

Arguments:
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
ATOMScalar coarray or coindexed variable of either integer type with ATOMIC_INT_KIND kind or logical type with ATOMIC_LOGICAL_KIND kind.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  logical(atomic_logical_kind) :: atom[*]
  logical :: val
  call atomic_ref (atom, .false.)
  ! ...
  call atomic_ref (atom, val)
  if (val) then
    print *, "Obtained"
  end if
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_CAS — Atomic compare and swap, ISO_FORTRAN_ENV, ATOMIC_FETCH_ADD — Atomic ADD operation with prior fetch, ATOMIC_FETCH_AND — Atomic bitwise AND operation with prior fetch, ATOMIC_FETCH_OR — Atomic bitwise OR operation with prior fetch, ATOMIC_FETCH_XOR — Atomic bitwise XOR operation with prior fetch


9.38 ATOMIC_XOR — Atomic bitwise OR operation

Description:

ATOMIC_AND(ATOM, VALUE) atomically defines ATOM with the bitwise XOR between the values of ATOM and VALUE. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value; in particular, for a coindexed ATOM, if the remote image has stopped, it is assigned the value of ISO_FORTRAN_ENV’s STAT_STOPPED_IMAGE and if the remote image has failed, the value STAT_FAILED_IMAGE.

Standard:

TS 18508 or later

Class:

Atomic subroutine

Syntax:

CALL ATOMIC_XOR (ATOM, VALUE [, STAT])

Arguments:
ATOMScalar coarray or coindexed variable of integer type with ATOMIC_INT_KIND kind.
VALUEScalar of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  integer(atomic_int_kind) :: atom[*]
  call atomic_xor (atom[1], int(b'10100011101'))
end program atomic
See also:

ATOMIC_DEFINE — Setting a variable atomically, ATOMIC_FETCH_XOR — Atomic bitwise XOR operation with prior fetch, ISO_FORTRAN_ENV, ATOMIC_ADD — Atomic ADD operation, ATOMIC_OR — Atomic bitwise OR operation, ATOMIC_XOR — Atomic bitwise OR operation


9.39 BACKTRACE — Show a backtrace

Description:

BACKTRACE shows a backtrace at an arbitrary place in user code. Program execution continues normally afterwards. The backtrace information is printed to the unit corresponding to ERROR_UNIT in ISO_FORTRAN_ENV.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL BACKTRACE

Arguments:

None

See also:

ABORT — Abort the program


9.40 BESSEL_J0 — Bessel function of the first kind of order 0

Description:

BESSEL_J0(X) computes the Bessel function of the first kind of order 0 of X. This function is available under the name BESJ0 as a GNU extension.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = BESSEL_J0(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type REAL and lies in the range - 0.4027... \leq Bessel (0,x) \leq 1. It has the same kind as X.

Example:
program test_besj0
  real(8) :: x = 0.0_8
  x = bessel_j0(x)
end program test_besj0
Specific names:
NameArgumentReturn typeStandard
DBESJ0(X)REAL(8) XREAL(8)GNU extension

9.41 BESSEL_J1 — Bessel function of the first kind of order 1

Description:

BESSEL_J1(X) computes the Bessel function of the first kind of order 1 of X. This function is available under the name BESJ1 as a GNU extension.

Standard:

Fortran 2008

Class:

Elemental function

Syntax:

RESULT = BESSEL_J1(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type REAL and lies in the range - 0.5818... \leq Bessel (0,x) \leq 0.5818 . It has the same kind as X.

Example:
program test_besj1
  real(8) :: x = 1.0_8
  x = bessel_j1(x)
end program test_besj1
Specific names:
NameArgumentReturn typeStandard
DBESJ1(X)REAL(8) XREAL(8)GNU extension

9.42 BESSEL_JN — Bessel function of the first kind

Description:

BESSEL_JN(N, X) computes the Bessel function of the first kind of order N of X. This function is available under the name BESJN as a GNU extension. If N and X are arrays, their ranks and shapes shall conform.

BESSEL_JN(N1, N2, X) returns an array with the Bessel functions of the first kind of the orders N1 to N2.

Standard:

Fortran 2008 and later, negative N is allowed as GNU extension

Class:

Elemental function, except for the transformational function BESSEL_JN(N1, N2, X)

Syntax:
RESULT = BESSEL_JN(N, X)
RESULT = BESSEL_JN(N1, N2, X)
Arguments:
NShall be a scalar or an array of type INTEGER.
N1Shall be a non-negative scalar of type INTEGER.
N2Shall be a non-negative scalar of type INTEGER.
XShall be a scalar or an array of type REAL; for BESSEL_JN(N1, N2, X) it shall be scalar.
Return value:

The return value is a scalar of type REAL. It has the same kind as X.

Note:

The transformational function uses a recurrence algorithm which might, for some values of X, lead to different results than calls to the elemental function.

Example:
program test_besjn
  real(8) :: x = 1.0_8
  x = bessel_jn(5,x)
end program test_besjn
Specific names:
NameArgumentReturn typeStandard
DBESJN(N, X)INTEGER NREAL(8)GNU extension
REAL(8) X

9.43 BESSEL_Y0 — Bessel function of the second kind of order 0

Description:

BESSEL_Y0(X) computes the Bessel function of the second kind of order 0 of X. This function is available under the name BESY0 as a GNU extension.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = BESSEL_Y0(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type REAL. It has the same kind as X.

Example:
program test_besy0
  real(8) :: x = 0.0_8
  x = bessel_y0(x)
end program test_besy0
Specific names:
NameArgumentReturn typeStandard
DBESY0(X)REAL(8) XREAL(8)GNU extension

9.44 BESSEL_Y1 — Bessel function of the second kind of order 1

Description:

BESSEL_Y1(X) computes the Bessel function of the second kind of order 1 of X. This function is available under the name BESY1 as a GNU extension.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = BESSEL_Y1(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type REAL. It has the same kind as X.

Example:
program test_besy1
  real(8) :: x = 1.0_8
  x = bessel_y1(x)
end program test_besy1
Specific names:
NameArgumentReturn typeStandard
DBESY1(X)REAL(8) XREAL(8)GNU extension

9.45 BESSEL_YN — Bessel function of the second kind

Description:

BESSEL_YN(N, X) computes the Bessel function of the second kind of order N of X. This function is available under the name BESYN as a GNU extension. If N and X are arrays, their ranks and shapes shall conform.

BESSEL_YN(N1, N2, X) returns an array with the Bessel functions of the first kind of the orders N1 to N2.

Standard:

Fortran 2008 and later, negative N is allowed as GNU extension

Class:

Elemental function, except for the transformational function BESSEL_YN(N1, N2, X)

Syntax:
RESULT = BESSEL_YN(N, X)
RESULT = BESSEL_YN(N1, N2, X)
Arguments:
NShall be a scalar or an array of type INTEGER .
N1Shall be a non-negative scalar of type INTEGER.
N2Shall be a non-negative scalar of type INTEGER.
XShall be a scalar or an array of type REAL; for BESSEL_YN(N1, N2, X) it shall be scalar.
Return value:

The return value is a scalar of type REAL. It has the same kind as X.

Note:

The transformational function uses a recurrence algorithm which might, for some values of X, lead to different results than calls to the elemental function.

Example:
program test_besyn
  real(8) :: x = 1.0_8
  x = bessel_yn(5,x)
end program test_besyn
Specific names:
NameArgumentReturn typeStandard
DBESYN(N,X)INTEGER NREAL(8)GNU extension
REAL(8) X

9.46 BGE — Bitwise greater than or equal to

Description:

Determines whether an integral is a bitwise greater than or equal to another.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = BGE(I, J)

Arguments:
IShall be of INTEGER type.
JShall be of INTEGER type, and of the same kind as I.
Return value:

The return value is of type LOGICAL and of the default kind.

See also:

BGT — Bitwise greater than, BLE — Bitwise less than or equal to, BLT — Bitwise less than


9.47 BGT — Bitwise greater than

Description:

Determines whether an integral is a bitwise greater than another.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = BGT(I, J)

Arguments:
IShall be of INTEGER type.
JShall be of INTEGER type, and of the same kind as I.
Return value:

The return value is of type LOGICAL and of the default kind.

See also:

BGE — Bitwise greater than or equal to, BLE — Bitwise less than or equal to, BLT — Bitwise less than


9.48 BIT_SIZE — Bit size inquiry function

Description:

BIT_SIZE(I) returns the number of bits (integer precision plus sign bit) represented by the type of I. The result of BIT_SIZE(I) is independent of the actual value of I.

Standard:

Fortran 90 and later

Class:

Inquiry function

Syntax:

RESULT = BIT_SIZE(I)

Arguments:
IThe type shall be INTEGER.
Return value:

The return value is of type INTEGER

Example:
program test_bit_size
    integer :: i = 123
    integer :: size
    size = bit_size(i)
    print *, size
end program test_bit_size

9.49 BLE — Bitwise less than or equal to

Description:

Determines whether an integral is a bitwise less than or equal to another.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = BLE(I, J)

Arguments:
IShall be of INTEGER type.
JShall be of INTEGER type, and of the same kind as I.
Return value:

The return value is of type LOGICAL and of the default kind.

See also:

BGT — Bitwise greater than, BGE — Bitwise greater than or equal to, BLT — Bitwise less than


9.50 BLT — Bitwise less than

Description:

Determines whether an integral is a bitwise less than another.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = BLT(I, J)

Arguments:
IShall be of INTEGER type.
JShall be of INTEGER type, and of the same kind as I.
Return value:

The return value is of type LOGICAL and of the default kind.

See also:

BGE — Bitwise greater than or equal to, BGT — Bitwise greater than, BLE — Bitwise less than or equal to


9.51 BTEST — Bit test function

Description:

BTEST(I,POS) returns logical .TRUE. if the bit at POS in I is set. The counting of the bits starts at 0.

Standard:

Fortran 90 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = BTEST(I, POS)

Arguments:
IThe type shall be INTEGER.
POSThe type shall be INTEGER.
Return value:

The return value is of type LOGICAL

Example:
program test_btest
    integer :: i = 32768 + 1024 + 64
    integer :: pos
    logical :: bool
    do pos=0,16
        bool = btest(i, pos) 
        print *, pos, bool
    end do
end program test_btest
Specific names:
NameArgumentReturn typeStandard
BTEST(I,POS)INTEGER I,POSLOGICALFortran 95 and later
BBTEST(I,POS)INTEGER(1) I,POSLOGICAL(1)GNU extension
BITEST(I,POS)INTEGER(2) I,POSLOGICAL(2)GNU extension
BJTEST(I,POS)INTEGER(4) I,POSLOGICAL(4)GNU extension
BKTEST(I,POS)INTEGER(8) I,POSLOGICAL(8)GNU extension

9.52 C_ASSOCIATED — Status of a C pointer

Description:

C_ASSOCIATED(c_ptr_1[, c_ptr_2]) determines the status of the C pointer c_ptr_1 or if c_ptr_1 is associated with the target c_ptr_2.

Standard:

Fortran 2003 and later

Class:

Inquiry function

Syntax:

RESULT = C_ASSOCIATED(c_ptr_1[, c_ptr_2])

Arguments:
c_ptr_1Scalar of the type C_PTR or C_FUNPTR.
c_ptr_2(Optional) Scalar of the same type as c_ptr_1.
Return value:

The return value is of type LOGICAL; it is .false. if either c_ptr_1 is a C NULL pointer or if c_ptr1 and c_ptr_2 point to different addresses.

Example:
subroutine association_test(a,b)
  use iso_c_binding, only: c_associated, c_loc, c_ptr
  implicit none
  real, pointer :: a
  type(c_ptr) :: b
  if(c_associated(b, c_loc(a))) &
     stop 'b and a do not point to same target'
end subroutine association_test
See also:

C_LOC — Obtain the C address of an object, C_FUNLOC — Obtain the C address of a procedure


9.53 C_F_POINTER — Convert C into Fortran pointer

Description:

C_F_POINTER(CPTR, FPTR[, SHAPE]) assigns the target of the C pointer CPTR to the Fortran pointer FPTR and specifies its shape.

Standard:

Fortran 2003 and later

Class:

Subroutine

Syntax:

CALL C_F_POINTER(CPTR, FPTR[, SHAPE])

Arguments:
CPTRscalar of the type C_PTR. It is INTENT(IN).
FPTRpointer interoperable with cptr. It is INTENT(OUT).
SHAPE(Optional) Rank-one array of type INTEGER with INTENT(IN). It shall be present if and only if fptr is an array. The size must be equal to the rank of fptr.
Example:
program main
  use iso_c_binding
  implicit none
  interface
    subroutine my_routine(p) bind(c,name='myC_func')
      import :: c_ptr
      type(c_ptr), intent(out) :: p
    end subroutine
  end interface
  type(c_ptr) :: cptr
  real,pointer :: a(:)
  call my_routine(cptr)
  call c_f_pointer(cptr, a, [12])
end program main
See also:

C_LOC — Obtain the C address of an object, C_F_PROCPOINTER — Convert C into Fortran procedure pointer


9.54 C_F_PROCPOINTER — Convert C into Fortran procedure pointer

Description:

C_F_PROCPOINTER(CPTR, FPTR) Assign the target of the C function pointer CPTR to the Fortran procedure pointer FPTR.

Standard:

Fortran 2003 and later

Class:

Subroutine

Syntax:

CALL C_F_PROCPOINTER(cptr, fptr)

Arguments:
CPTRscalar of the type C_FUNPTR. It is INTENT(IN).
FPTRprocedure pointer interoperable with cptr. It is INTENT(OUT).
Example:
program main
  use iso_c_binding
  implicit none
  abstract interface
    function func(a)
      import :: c_float
      real(c_float), intent(in) :: a
      real(c_float) :: func
    end function
  end interface
  interface
     function getIterFunc() bind(c,name="getIterFunc")
       import :: c_funptr
       type(c_funptr) :: getIterFunc
     end function
  end interface
  type(c_funptr) :: cfunptr
  procedure(func), pointer :: myFunc
  cfunptr = getIterFunc()
  call c_f_procpointer(cfunptr, myFunc)
end program main
See also:

C_LOC — Obtain the C address of an object, C_F_POINTER — Convert C into Fortran pointer


9.55 C_FUNLOC — Obtain the C address of a procedure

Description:

C_FUNLOC(x) determines the C address of the argument.

Standard:

Fortran 2003 and later

Class:

Inquiry function

Syntax:

RESULT = C_FUNLOC(x)

Arguments:
xInteroperable function or pointer to such function.
Return value:

The return value is of type C_FUNPTR and contains the C address of the argument.

Example:
module x
  use iso_c_binding
  implicit none
contains
  subroutine sub(a) bind(c)
    real(c_float) :: a
    a = sqrt(a)+5.0
  end subroutine sub
end module x
program main
  use iso_c_binding
  use x
  implicit none
  interface
    subroutine my_routine(p) bind(c,name='myC_func')
      import :: c_funptr
      type(c_funptr), intent(in) :: p
    end subroutine
  end interface
  call my_routine(c_funloc(sub))
end program main
See also:

C_ASSOCIATED — Status of a C pointer, C_LOC — Obtain the C address of an object, C_F_POINTER — Convert C into Fortran pointer, C_F_PROCPOINTER — Convert C into Fortran procedure pointer


9.56 C_LOC — Obtain the C address of an object

Description:

C_LOC(X) determines the C address of the argument.

Standard:

Fortran 2003 and later

Class:

Inquiry function

Syntax:

RESULT = C_LOC(X)

Arguments:
XShall have either the POINTER or TARGET attribute. It shall not be a coindexed object. It shall either be a variable with interoperable type and kind type parameters, or be a scalar, nonpolymorphic variable with no length type parameters.
Return value:

The return value is of type C_PTR and contains the C address of the argument.

Example:
subroutine association_test(a,b)
  use iso_c_binding, only: c_associated, c_loc, c_ptr
  implicit none
  real, pointer :: a
  type(c_ptr) :: b
  if(c_associated(b, c_loc(a))) &
     stop 'b and a do not point to same target'
end subroutine association_test
See also:

C_ASSOCIATED — Status of a C pointer, C_FUNLOC — Obtain the C address of a procedure, C_F_POINTER — Convert C into Fortran pointer, C_F_PROCPOINTER — Convert C into Fortran procedure pointer


9.57 C_SIZEOF — Size in bytes of an expression

Description:

C_SIZEOF(X) calculates the number of bytes of storage the expression X occupies.

Standard:

Fortran 2008

Class:

Inquiry function of the module ISO_C_BINDING

Syntax:

N = C_SIZEOF(X)

Arguments:
XThe argument shall be an interoperable data entity.
Return value:

The return value is of type integer and of the system-dependent kind C_SIZE_T (from the ISO_C_BINDING module). Its value is the number of bytes occupied by the argument. If the argument has the POINTER attribute, the number of bytes of the storage area pointed to is returned. If the argument is of a derived type with POINTER or ALLOCATABLE components, the return value does not account for the sizes of the data pointed to by these components.

Example:
   use iso_c_binding
   integer(c_int) :: i
   real(c_float) :: r, s(5)
   print *, (c_sizeof(s)/c_sizeof(r) == 5)
   end

The example will print T unless you are using a platform where default REAL variables are unusually padded.

See also:

SIZEOF — Size in bytes of an expression, STORAGE_SIZE — Storage size in bits


9.58 CEILING — Integer ceiling function

Description:

CEILING(A) returns the least integer greater than or equal to A.

Standard:

Fortran 95 and later

Class:

Elemental function

Syntax:

RESULT = CEILING(A [, KIND])

Arguments:
AThe type shall be REAL.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER(KIND) if KIND is present and a default-kind INTEGER otherwise.

Example:
program test_ceiling
    real :: x = 63.29
    real :: y = -63.59
    print *, ceiling(x) ! returns 64
    print *, ceiling(y) ! returns -63
end program test_ceiling
See also:

FLOOR — Integer floor function, NINT — Nearest whole number


9.59 CHAR — Character conversion function

Description:

CHAR(I [, KIND]) returns the character represented by the integer I.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = CHAR(I [, KIND])

Arguments:
IThe type shall be INTEGER.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type CHARACTER(1)

Example:
program test_char
    integer :: i = 74
    character(1) :: c
    c = char(i)
    print *, i, c ! returns 'J'
end program test_char
Specific names:
NameArgumentReturn typeStandard
CHAR(I)INTEGER ICHARACTER(LEN=1)Fortran 77 and later
Note:

See ICHAR — Character-to-integer conversion function for a discussion of converting between numerical values and formatted string representations.

See also:

ACHAR — Character in ASCII collating sequence, IACHAR — Code in ASCII collating sequence, ICHAR — Character-to-integer conversion function


9.60 CHDIR — Change working directory

Description:

Change current working directory to a specified path.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL CHDIR(NAME [, STATUS])
STATUS = CHDIR(NAME)
Arguments:
NAMEThe type shall be CHARACTER of default kind and shall specify a valid path within the file system.
STATUS(Optional) INTEGER status flag of the default kind. Returns 0 on success, and a system specific and nonzero error code otherwise.
Example:
PROGRAM test_chdir
  CHARACTER(len=255) :: path
  CALL getcwd(path)
  WRITE(*,*) TRIM(path)
  CALL chdir("/tmp")
  CALL getcwd(path)
  WRITE(*,*) TRIM(path)
END PROGRAM
See also:

GETCWD — Get current working directory


9.61 CHMOD — Change access permissions of files

Description:

CHMOD changes the permissions of a file.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL CHMOD(NAME, MODE[, STATUS])
STATUS = CHMOD(NAME, MODE)
Arguments:
NAMEScalar CHARACTER of default kind with the file name. Trailing blanks are ignored unless the character achar(0) is present, then all characters up to and excluding achar(0) are used as the file name.
MODEScalar CHARACTER of default kind giving the file permission. MODE uses the same syntax as the chmod utility as defined by the POSIX standard. The argument shall either be a string of a nonnegative octal number or a symbolic mode.
STATUS(optional) scalar INTEGER, which is 0 on success and nonzero otherwise.
Return value:

In either syntax, STATUS is set to 0 on success and nonzero otherwise.

Example:

CHMOD as subroutine

program chmod_test
  implicit none
  integer :: status
  call chmod('test.dat','u+x',status)
  print *, 'Status: ', status
end program chmod_test

CHMOD as function:

program chmod_test
  implicit none
  integer :: status
  status = chmod('test.dat','u+x')
  print *, 'Status: ', status
end program chmod_test

9.62 CMPLX — Complex conversion function

Description:

CMPLX(X [, Y [, KIND]]) returns a complex number where X is converted to the real component. If Y is present it is converted to the imaginary component. If Y is not present then the imaginary component is set to 0.0. If X is complex then Y must not be present.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = CMPLX(X [, Y [, KIND]])

Arguments:
XThe type may be INTEGER, REAL, or COMPLEX.
Y(Optional; only allowed if X is not COMPLEX.) May be INTEGER or REAL.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of COMPLEX type, with a kind equal to KIND if it is specified. If KIND is not specified, the result is of the default COMPLEX kind, regardless of the kinds of X and Y.

Example:
program test_cmplx
    integer :: i = 42
    real :: x = 3.14
    complex :: z
    z = cmplx(i, x)
    print *, z, cmplx(x)
end program test_cmplx
See also:

COMPLEX — Complex conversion function


9.63 CO_BROADCAST — Copy a value to all images the current set of images

Description:

CO_BROADCAST copies the value of argument A on the image with image index SOURCE_IMAGE to all images in the current team. A becomes defined as if by intrinsic assignment. If the execution was successful and STAT is present, it is assigned the value zero. If the execution failed, STAT gets assigned a nonzero value and, if present, ERRMSG gets assigned a value describing the occurred error.

Standard:

Technical Specification (TS) 18508 or later

Class:

Collective subroutine

Syntax:

CALL CO_BROADCAST(A, SOURCE_IMAGE [, STAT, ERRMSG])

Arguments:
AINTENT(INOUT) argument; shall have the same dynamic type and type parameters on all images of the current team. If it is an array, it shall have the same shape on all images.
SOURCE_IMAGEa scalar integer expression. It shall have the same value on all images and refer to an image of the current team.
STAT(optional) a scalar integer variable
ERRMSG(optional) a scalar character variable
Example:
program test
  integer :: val(3)
  if (this_image() == 1) then
    val = [1, 5, 3]
  end if
  call co_broadcast (val, source_image=1)
  print *, this_image, ":", val
end program test
See also:

CO_MAX — Maximal value on the current set of images, CO_MIN — Minimal value on the current set of images, CO_SUM — Sum of values on the current set of images, CO_REDUCE — Reduction of values on the current set of images


9.64 CO_MAX — Maximal value on the current set of images

Description:

CO_MAX determines element-wise the maximal value of A on all images of the current team. If RESULT_IMAGE is present, the maximum values are returned in A on the specified image only and the value of A on the other images become undefined. If RESULT_IMAGE is not present, the value is returned on all images. If the execution was successful and STAT is present, it is assigned the value zero. If the execution failed, STAT gets assigned a nonzero value and, if present, ERRMSG gets assigned a value describing the occurred error.

Standard:

Technical Specification (TS) 18508 or later

Class:

Collective subroutine

Syntax:

CALL CO_MAX(A [, RESULT_IMAGE, STAT, ERRMSG])

Arguments:
Ashall be an integer, real or character variable, which has the same type and type parameters on all images of the team.
RESULT_IMAGE(optional) a scalar integer expression; if present, it shall have the same value on all images and refer to an image of the current team.
STAT(optional) a scalar integer variable
ERRMSG(optional) a scalar character variable
Example:
program test
  integer :: val
  val = this_image ()
  call co_max (val, result_image=1)
  if (this_image() == 1) then
    write(*,*) "Maximal value", val  ! prints num_images()
  end if
end program test
See also:

CO_MIN — Minimal value on the current set of images, CO_SUM — Sum of values on the current set of images, CO_REDUCE — Reduction of values on the current set of images, CO_BROADCAST — Copy a value to all images the current set of images


9.65 CO_MIN — Minimal value on the current set of images

Description:

CO_MIN determines element-wise the minimal value of A on all images of the current team. If RESULT_IMAGE is present, the minimal values are returned in A on the specified image only and the value of A on the other images become undefined. If RESULT_IMAGE is not present, the value is returned on all images. If the execution was successful and STAT is present, it is assigned the value zero. If the execution failed, STAT gets assigned a nonzero value and, if present, ERRMSG gets assigned a value describing the occurred error.

Standard:

Technical Specification (TS) 18508 or later

Class:

Collective subroutine

Syntax:

CALL CO_MIN(A [, RESULT_IMAGE, STAT, ERRMSG])

Arguments:
Ashall be an integer, real or character variable, which has the same type and type parameters on all images of the team.
RESULT_IMAGE(optional) a scalar integer expression; if present, it shall have the same value on all images and refer to an image of the current team.
STAT(optional) a scalar integer variable
ERRMSG(optional) a scalar character variable
Example:
program test
  integer :: val
  val = this_image ()
  call co_min (val, result_image=1)
  if (this_image() == 1) then
    write(*,*) "Minimal value", val  ! prints 1
  end if
end program test
See also:

CO_MAX — Maximal value on the current set of images, CO_SUM — Sum of values on the current set of images, CO_REDUCE — Reduction of values on the current set of images, CO_BROADCAST — Copy a value to all images the current set of images


9.66 CO_REDUCE — Reduction of values on the current set of images

Description:

CO_REDUCE determines element-wise the reduction of the value of A on all images of the current team. The pure function passed as OPERATOR is used to pairwise reduce the values of A by passing either the value of A of different images or the result values of such a reduction as argument. If A is an array, the deduction is done element wise. If RESULT_IMAGE is present, the result values are returned in A on the specified image only and the value of A on the other images become undefined. If RESULT_IMAGE is not present, the value is returned on all images. If the execution was successful and STAT is present, it is assigned the value zero. If the execution failed, STAT gets assigned a nonzero value and, if present, ERRMSG gets assigned a value describing the occurred error.

Standard:

Technical Specification (TS) 18508 or later

Class:

Collective subroutine

Syntax:

CALL CO_REDUCE(A, OPERATOR, [, RESULT_IMAGE, STAT, ERRMSG])

Arguments:
Ais an INTENT(INOUT) argument and shall be nonpolymorphic. If it is allocatable, it shall be allocated; if it is a pointer, it shall be associated. A shall have the same type and type parameters on all images of the team; if it is an array, it shall have the same shape on all images.
OPERATORpure function with two scalar nonallocatable arguments, which shall be nonpolymorphic and have the same type and type parameters as A. The function shall return a nonallocatable scalar of the same type and type parameters as A. The function shall be the same on all images and with regards to the arguments mathematically commutative and associative. Note that OPERATOR may not be an elemental function, unless it is an intrisic function.
RESULT_IMAGE(optional) a scalar integer expression; if present, it shall have the same value on all images and refer to an image of the current team.
STAT(optional) a scalar integer variable
ERRMSG(optional) a scalar character variable
Example:
program test
  integer :: val
  val = this_image ()
  call co_reduce (val, result_image=1, operator=myprod)
  if (this_image() == 1) then
    write(*,*) "Product value", val  ! prints num_images() factorial
  end if
contains
  pure function myprod(a, b)
    integer, value :: a, b
    integer :: myprod
    myprod = a * b
  end function myprod
end program test
Note:

While the rules permit in principle an intrinsic function, none of the intrinsics in the standard fulfill the criteria of having a specific function, which takes two arguments of the same type and returning that type as result.

See also:

CO_MIN — Minimal value on the current set of images, CO_MAX — Maximal value on the current set of images, CO_SUM — Sum of values on the current set of images, CO_BROADCAST — Copy a value to all images the current set of images


9.67 CO_SUM — Sum of values on the current set of images

Description:

CO_SUM sums up the values of each element of A on all images of the current team. If RESULT_IMAGE is present, the summed-up values are returned in A on the specified image only and the value of A on the other images become undefined. If RESULT_IMAGE is not present, the value is returned on all images. If the execution was successful and STAT is present, it is assigned the value zero. If the execution failed, STAT gets assigned a nonzero value and, if present, ERRMSG gets assigned a value describing the occurred error.

Standard:

Technical Specification (TS) 18508 or later

Class:

Collective subroutine

Syntax:

CALL CO_SUM(A [, RESULT_IMAGE, STAT, ERRMSG])

Arguments:
Ashall be an integer, real or complex variable, which has the same type and type parameters on all images of the team.
RESULT_IMAGE(optional) a scalar integer expression; if present, it shall have the same value on all images and refer to an image of the current team.
STAT(optional) a scalar integer variable
ERRMSG(optional) a scalar character variable
Example:
program test
  integer :: val
  val = this_image ()
  call co_sum (val, result_image=1)
  if (this_image() == 1) then
    write(*,*) "The sum is ", val ! prints (n**2 + n)/2,
                                  ! with n = num_images()
  end if
end program test
See also:

CO_MAX — Maximal value on the current set of images, CO_MIN — Minimal value on the current set of images, CO_REDUCE — Reduction of values on the current set of images, CO_BROADCAST — Copy a value to all images the current set of images


9.68 COMMAND_ARGUMENT_COUNT — Get number of command line arguments

Description:

COMMAND_ARGUMENT_COUNT returns the number of arguments passed on the command line when the containing program was invoked.

Standard:

Fortran 2003 and later

Class:

Inquiry function

Syntax:

RESULT = COMMAND_ARGUMENT_COUNT()

Arguments:
None
Return value:

The return value is an INTEGER of default kind.

Example:
program test_command_argument_count
    integer :: count
    count = command_argument_count()
    print *, count
end program test_command_argument_count
See also:

GET_COMMAND — Get the entire command line, GET_COMMAND_ARGUMENT — Get command line arguments


9.69 COMPILER_OPTIONS — Options passed to the compiler

Description:

COMPILER_OPTIONS returns a string with the options used for compiling.

Standard:

Fortran 2008

Class:

Inquiry function of the module ISO_FORTRAN_ENV

Syntax:

STR = COMPILER_OPTIONS()

Arguments:

None

Return value:

The return value is a default-kind string with system-dependent length. It contains the compiler flags used to compile the file, which called the COMPILER_OPTIONS intrinsic.

Example:
   use iso_fortran_env
   print '(4a)', 'This file was compiled by ', &
                 compiler_version(), ' using the options ', &
                 compiler_options()
   end
See also:

COMPILER_VERSION — Compiler version string, ISO_FORTRAN_ENV


9.70 COMPILER_VERSION — Compiler version string

Description:

COMPILER_VERSION returns a string with the name and the version of the compiler.

Standard:

Fortran 2008

Class:

Inquiry function of the module ISO_FORTRAN_ENV

Syntax:

STR = COMPILER_VERSION()

Arguments:

None

Return value:

The return value is a default-kind string with system-dependent length. It contains the name of the compiler and its version number.

Example:
   use iso_fortran_env
   print '(4a)', 'This file was compiled by ', &
                 compiler_version(), ' using the options ', &
                 compiler_options()
   end
See also:

COMPILER_OPTIONS — Options passed to the compiler, ISO_FORTRAN_ENV


9.71 COMPLEX — Complex conversion function

Description:

COMPLEX(X, Y) returns a complex number where X is converted to the real component and Y is converted to the imaginary component.

Standard:

GNU extension

Class:

Elemental function

Syntax:

RESULT = COMPLEX(X, Y)

Arguments:
XThe type may be INTEGER or REAL.
YThe type may be INTEGER or REAL.
Return value:

If X and Y are both of INTEGER type, then the return value is of default COMPLEX type.

If X and Y are of REAL type, or one is of REAL type and one is of INTEGER type, then the return value is of COMPLEX type with a kind equal to that of the REAL argument with the highest precision.

Example:
program test_complex
    integer :: i = 42
    real :: x = 3.14
    print *, complex(i, x)
end program test_complex
See also:

CMPLX — Complex conversion function


9.72 CONJG — Complex conjugate function

Description:

CONJG(Z) returns the conjugate of Z. If Z is (x, y) then the result is (x, -y)

Standard:

Fortran 77 and later, has an overload that is a GNU extension

Class:

Elemental function

Syntax:

Z = CONJG(Z)

Arguments:
ZThe type shall be COMPLEX.
Return value:

The return value is of type COMPLEX.

Example:
program test_conjg
    complex :: z = (2.0, 3.0)
    complex(8) :: dz = (2.71_8, -3.14_8)
    z= conjg(z)
    print *, z
    dz = dconjg(dz)
    print *, dz
end program test_conjg
Specific names:
NameArgumentReturn typeStandard
DCONJG(Z)COMPLEX(8) ZCOMPLEX(8)GNU extension

9.73 COS — Cosine function

Description:

COS(X) computes the cosine of X.

Standard:

Fortran 77 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = COS(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value is of the same type and kind as X. The real part of the result is in radians. If X is of the type REAL, the return value lies in the range -1 \leq \cos (x) \leq 1.

Example:
program test_cos
  real :: x = 0.0
  x = cos(x)
end program test_cos
Specific names:
NameArgumentReturn typeStandard
COS(X)REAL(4) XREAL(4)Fortran 77 and later
DCOS(X)REAL(8) XREAL(8)Fortran 77 and later
CCOS(X)COMPLEX(4) XCOMPLEX(4)Fortran 77 and later
ZCOS(X)COMPLEX(8) XCOMPLEX(8)GNU extension
CDCOS(X)COMPLEX(8) XCOMPLEX(8)GNU extension
See also:

Inverse function: ACOS — Arccosine function Degrees function: COSD — Cosine function, degrees


9.74 COSD — Cosine function, degrees

Description:

COSD(X) computes the cosine of X in degrees.

This function is for compatibility only and should be avoided in favor of standard constructs wherever possible.

Standard:

GNU extension, enabled with -fdec-math.

Class:

Elemental function

Syntax:

RESULT = COSD(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value is of the same type and kind as X. The real part of the result is in degrees. If X is of the type REAL, the return value lies in the range -1 \leq \cosd (x) \leq 1.

Example:
program test_cosd
  real :: x = 0.0
  x = cosd(x)
end program test_cosd
Specific names:
NameArgumentReturn typeStandard
COSD(X)REAL(4) XREAL(4)GNU extension
DCOSD(X)REAL(8) XREAL(8)GNU extension
CCOSD(X)COMPLEX(4) XCOMPLEX(4)GNU extension
ZCOSD(X)COMPLEX(8) XCOMPLEX(8)GNU extension
CDCOSD(X)COMPLEX(8) XCOMPLEX(8)GNU extension
See also:

Inverse function: ACOSD — Arccosine function, degrees Radians function: COS — Cosine function


9.75 COSH — Hyperbolic cosine function

Description:

COSH(X) computes the hyperbolic cosine of X.

Standard:

Fortran 77 and later, for a complex argument Fortran 2008 or later

Class:

Elemental function

Syntax:

X = COSH(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value has same type and kind as X. If X is complex, the imaginary part of the result is in radians. If X is REAL, the return value has a lower bound of one, \cosh (x) \geq 1.

Example:
program test_cosh
  real(8) :: x = 1.0_8
  x = cosh(x)
end program test_cosh
Specific names:
NameArgumentReturn typeStandard
COSH(X)REAL(4) XREAL(4)Fortran 77 and later
DCOSH(X)REAL(8) XREAL(8)Fortran 77 and later
See also:

Inverse function: ACOSH — Inverse hyperbolic cosine function


9.76 COTAN — Cotangent function

Description:

COTAN(X) computes the cotangent of X. Equivalent to COS(x) divided by SIN(x), or 1 / TAN(x).

This function is for compatibility only and should be avoided in favor of standard constructs wherever possible.

Standard:

GNU extension, enabled with -fdec-math.

Class:

Elemental function

Syntax:

RESULT = COTAN(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value has same type and kind as X, and its value is in radians.

Example:
program test_cotan
  real(8) :: x = 0.165_8
  x = cotan(x)
end program test_cotan
Specific names:
NameArgumentReturn typeStandard
COTAN(X)REAL(4) XREAL(4)GNU extension
DCOTAN(X)REAL(8) XREAL(8)GNU extension
See also:

Converse function: TAN — Tangent function Degrees function: COTAND — Cotangent function, degrees


9.77 COTAND — Cotangent function, degrees

Description:

COTAND(X) computes the cotangent of X in degrees. Equivalent to COSD(x) divided by SIND(x), or 1 / TAND(x).

Standard:

GNU extension, enabled with -fdec-math.

This function is for compatibility only and should be avoided in favor of standard constructs wherever possible.

Class:

Elemental function

Syntax:

RESULT = COTAND(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value has same type and kind as X, and its value is in degrees.

Example:
program test_cotand
  real(8) :: x = 0.165_8
  x = cotand(x)
end program test_cotand
Specific names:
NameArgumentReturn typeStandard
COTAND(X)REAL(4) XREAL(4)GNU extension
DCOTAND(X)REAL(8) XREAL(8)GNU extension
See also:

Converse function: TAND — Tangent function, degrees Radians function: COTAN — Cotangent function


9.78 COUNT — Count function

Description:

Counts the number of .TRUE. elements in a logical MASK, or, if the DIM argument is supplied, counts the number of elements along each row of the array in the DIM direction. If the array has zero size, or all of the elements of MASK are .FALSE., then the result is 0.

Standard:

Fortran 90 and later, with KIND argument Fortran 2003 and later

Class:

Transformational function

Syntax:

RESULT = COUNT(MASK [, DIM, KIND])

Arguments:
MASKThe type shall be LOGICAL.
DIM(Optional) The type shall be INTEGER.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is present, the result is an array with a rank one less than the rank of ARRAY, and a size corresponding to the shape of ARRAY with the DIM dimension removed.

Example:
program test_count
    integer, dimension(2,3) :: a, b
    logical, dimension(2,3) :: mask
    a = reshape( (/ 1, 2, 3, 4, 5, 6 /), (/ 2, 3 /))
    b = reshape( (/ 0, 7, 3, 4, 5, 8 /), (/ 2, 3 /))
    print '(3i3)', a(1,:)
    print '(3i3)', a(2,:)
    print *
    print '(3i3)', b(1,:)
    print '(3i3)', b(2,:)
    print *
    mask = a.ne.b
    print '(3l3)', mask(1,:)
    print '(3l3)', mask(2,:)
    print *
    print '(3i3)', count(mask)
    print *
    print '(3i3)', count(mask, 1)
    print *
    print '(3i3)', count(mask, 2)
end program test_count

9.79 CPU_TIME — CPU elapsed time in seconds

Description:

Returns a REAL value representing the elapsed CPU time in seconds. This is useful for testing segments of code to determine execution time.

If a time source is available, time will be reported with microsecond resolution. If no time source is available, TIME is set to -1.0.

Note that TIME may contain a, system dependent, arbitrary offset and may not start with 0.0. For CPU_TIME, the absolute value is meaningless, only differences between subsequent calls to this subroutine, as shown in the example below, should be used.

Standard:

Fortran 95 and later

Class:

Subroutine

Syntax:

CALL CPU_TIME(TIME)

Arguments:
TIMEThe type shall be REAL with INTENT(OUT).
Return value:

None

Example:
program test_cpu_time
    real :: start, finish
    call cpu_time(start)
        ! put code to test here
    call cpu_time(finish)
    print '("Time = ",f6.3," seconds.")',finish-start
end program test_cpu_time
See also:

SYSTEM_CLOCK — Time function, DATE_AND_TIME — Date and time subroutine


9.80 CSHIFT — Circular shift elements of an array

Description:

CSHIFT(ARRAY, SHIFT [, DIM]) performs a circular shift on elements of ARRAY along the dimension of DIM. If DIM is omitted it is taken to be 1. DIM is a scalar of type INTEGER in the range of 1 \leq DIM \leq n) where n is the rank of ARRAY. If the rank of ARRAY is one, then all elements of ARRAY are shifted by SHIFT places. If rank is greater than one, then all complete rank one sections of ARRAY along the given dimension are shifted. Elements shifted out one end of each rank one section are shifted back in the other end.

Standard:

Fortran 90 and later

Class:

Transformational function

Syntax:

RESULT = CSHIFT(ARRAY, SHIFT [, DIM])

Arguments:
ARRAYShall be an array of any type.
SHIFTThe type shall be INTEGER.
DIMThe type shall be INTEGER.
Return value:

Returns an array of same type and rank as the ARRAY argument.

Example:
program test_cshift
    integer, dimension(3,3) :: a
    a = reshape( (/ 1, 2, 3, 4, 5, 6, 7, 8, 9 /), (/ 3, 3 /))
    print '(3i3)', a(1,:)
    print '(3i3)', a(2,:)
    print '(3i3)', a(3,:)    
    a = cshift(a, SHIFT=(/1, 2, -1/), DIM=2)
    print *
    print '(3i3)', a(1,:)
    print '(3i3)', a(2,:)
    print '(3i3)', a(3,:)
end program test_cshift

9.81 CTIME — Convert a time into a string

Description:

CTIME converts a system time value, such as returned by TIME8 — Time function (64-bit), to a string. The output will be of the form ‘Sat Aug 19 18:13:14 1995’.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL CTIME(TIME, RESULT).
RESULT = CTIME(TIME).
Arguments:
TIMEThe type shall be of type INTEGER.
RESULTThe type shall be of type CHARACTER and of default kind. It is an INTENT(OUT) argument. If the length of this variable is too short for the time and date string to fit completely, it will be blank on procedure return.
Return value:

The converted date and time as a string.

Example:
program test_ctime
    integer(8) :: i
    character(len=30) :: date
    i = time8()

    ! Do something, main part of the program
    
    call ctime(i,date)
    print *, 'Program was started on ', date
end program test_ctime
See Also:

DATE_AND_TIME — Date and time subroutine, GMTIME — Convert time to GMT info, LTIME — Convert time to local time info, TIME — Time function, TIME8 — Time function (64-bit)


9.82 DATE_AND_TIME — Date and time subroutine

Description:

DATE_AND_TIME(DATE, TIME, ZONE, VALUES) gets the corresponding date and time information from the real-time system clock. DATE is INTENT(OUT) and has form ccyymmdd. TIME is INTENT(OUT) and has form hhmmss.sss. ZONE is INTENT(OUT) and has form (+-)hhmm, representing the difference with respect to Coordinated Universal Time (UTC). Unavailable time and date parameters return blanks.

VALUES is INTENT(OUT) and provides the following:

VALUE(1):The year
VALUE(2):The month
VALUE(3):The day of the month
VALUE(4):Time difference with UTC in minutes
VALUE(5):The hour of the day
VALUE(6):The minutes of the hour
VALUE(7):The seconds of the minute
VALUE(8):The milliseconds of the second
Standard:

Fortran 90 and later

Class:

Subroutine

Syntax:

CALL DATE_AND_TIME([DATE, TIME, ZONE, VALUES])

Arguments:
DATE(Optional) The type shall be CHARACTER(LEN=8) or larger, and of default kind.
TIME(Optional) The type shall be CHARACTER(LEN=10) or larger, and of default kind.
ZONE(Optional) The type shall be CHARACTER(LEN=5) or larger, and of default kind.
VALUES(Optional) The type shall be INTEGER(8).
Return value:

None

Example:
program test_time_and_date
    character(8)  :: date
    character(10) :: time
    character(5)  :: zone
    integer,dimension(8) :: values
    ! using keyword arguments
    call date_and_time(date,time,zone,values)
    call date_and_time(DATE=date,ZONE=zone)
    call date_and_time(TIME=time)
    call date_and_time(VALUES=values)
    print '(a,2x,a,2x,a)', date, time, zone
    print '(8i5)', values
end program test_time_and_date
See also:

CPU_TIME — CPU elapsed time in seconds, SYSTEM_CLOCK — Time function


9.83 DBLE — Double conversion function

Description:

DBLE(A) Converts A to double precision real type.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = DBLE(A)

Arguments:
AThe type shall be INTEGER, REAL, or COMPLEX.
Return value:

The return value is of type double precision real.

Example:
program test_dble
    real    :: x = 2.18
    integer :: i = 5
    complex :: z = (2.3,1.14)
    print *, dble(x), dble(i), dble(z)
end program test_dble
See also:

REAL — Convert to real type


9.84 DCMPLX — Double complex conversion function

Description:

DCMPLX(X [,Y]) returns a double complex number where X is converted to the real component. If Y is present it is converted to the imaginary component. If Y is not present then the imaginary component is set to 0.0. If X is complex then Y must not be present.

Standard:

GNU extension

Class:

Elemental function

Syntax:

RESULT = DCMPLX(X [, Y])

Arguments:
XThe type may be INTEGER, REAL, or COMPLEX.
Y(Optional if X is not COMPLEX.) May be INTEGER or REAL.
Return value:

The return value is of type COMPLEX(8)

Example:
program test_dcmplx
    integer :: i = 42
    real :: x = 3.14
    complex :: z
    z = cmplx(i, x)
    print *, dcmplx(i)
    print *, dcmplx(x)
    print *, dcmplx(z)
    print *, dcmplx(x,i)
end program test_dcmplx

9.85 DIGITS — Significant binary digits function

Description:

DIGITS(X) returns the number of significant binary digits of the internal model representation of X. For example, on a system using a 32-bit floating point representation, a default real number would likely return 24.

Standard:

Fortran 90 and later

Class:

Inquiry function

Syntax:

RESULT = DIGITS(X)

Arguments:
XThe type may be INTEGER or REAL.
Return value:

The return value is of type INTEGER.

Example:
program test_digits
    integer :: i = 12345
    real :: x = 3.143
    real(8) :: y = 2.33
    print *, digits(i)
    print *, digits(x)
    print *, digits(y)
end program test_digits

9.86 DIM — Positive difference

Description:

DIM(X,Y) returns the difference X-Y if the result is positive; otherwise returns zero.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = DIM(X, Y)

Arguments:
XThe type shall be INTEGER or REAL
YThe type shall be the same type and kind as X. (As a GNU extension, arguments of different kinds are permitted.)
Return value:

The return value is of type INTEGER or REAL. (As a GNU extension, kind is the largest kind of the actual arguments.)

Example:
program test_dim
    integer :: i
    real(8) :: x
    i = dim(4, 15)
    x = dim(4.345_8, 2.111_8)
    print *, i
    print *, x
end program test_dim
Specific names:
NameArgumentReturn typeStandard
DIM(X,Y)REAL(4) X, YREAL(4)Fortran 77 and later
IDIM(X,Y)INTEGER(4) X, YINTEGER(4)Fortran 77 and later
DDIM(X,Y)REAL(8) X, YREAL(8)Fortran 77 and later

9.87 DOT_PRODUCT — Dot product function

Description:

DOT_PRODUCT(VECTOR_A, VECTOR_B) computes the dot product multiplication of two vectors VECTOR_A and VECTOR_B. The two vectors may be either numeric or logical and must be arrays of rank one and of equal size. If the vectors are INTEGER or REAL, the result is SUM(VECTOR_A*VECTOR_B). If the vectors are COMPLEX, the result is SUM(CONJG(VECTOR_A)*VECTOR_B). If the vectors are LOGICAL, the result is ANY(VECTOR_A .AND. VECTOR_B).

Standard:

Fortran 90 and later

Class:

Transformational function

Syntax:

RESULT = DOT_PRODUCT(VECTOR_A, VECTOR_B)

Arguments:
VECTOR_AThe type shall be numeric or LOGICAL, rank 1.
VECTOR_BThe type shall be numeric if VECTOR_A is of numeric type or LOGICAL if VECTOR_A is of type LOGICAL. VECTOR_B shall be a rank-one array.
Return value:

If the arguments are numeric, the return value is a scalar of numeric type, INTEGER, REAL, or COMPLEX. If the arguments are LOGICAL, the return value is .TRUE. or .FALSE..

Example:
program test_dot_prod
    integer, dimension(3) :: a, b
    a = (/ 1, 2, 3 /)
    b = (/ 4, 5, 6 /)
    print '(3i3)', a
    print *
    print '(3i3)', b
    print *
    print *, dot_product(a,b)
end program test_dot_prod

9.88 DPROD — Double product function

Description:

DPROD(X,Y) returns the product X*Y.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = DPROD(X, Y)

Arguments:
XThe type shall be REAL.
YThe type shall be REAL.
Return value:

The return value is of type REAL(8).

Example:
program test_dprod
    real :: x = 5.2
    real :: y = 2.3
    real(8) :: d
    d = dprod(x,y)
    print *, d
end program test_dprod
Specific names:
NameArgumentReturn typeStandard
DPROD(X,Y)REAL(4) X, YREAL(8)Fortran 77 and later

9.89 DREAL — Double real part function

Description:

DREAL(Z) returns the real part of complex variable Z.

Standard:

GNU extension

Class:

Elemental function

Syntax:

RESULT = DREAL(A)

Arguments:
AThe type shall be COMPLEX(8).
Return value:

The return value is of type REAL(8).

Example:
program test_dreal
    complex(8) :: z = (1.3_8,7.2_8)
    print *, dreal(z)
end program test_dreal
See also:

AIMAG — Imaginary part of complex number


9.90 DSHIFTL — Combined left shift

Description:

DSHIFTL(I, J, SHIFT) combines bits of I and J. The rightmost SHIFT bits of the result are the leftmost SHIFT bits of J, and the remaining bits are the rightmost bits of I.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = DSHIFTL(I, J, SHIFT)

Arguments:
IShall be of type INTEGER or a BOZ constant.
JShall be of type INTEGER or a BOZ constant. If both I and J have integer type, then they shall have the same kind type parameter. I and J shall not both be BOZ constants.
SHIFTShall be of type INTEGER. It shall be nonnegative. If I is not a BOZ constant, then SHIFT shall be less than or equal to BIT_SIZE(I); otherwise, SHIFT shall be less than or equal to BIT_SIZE(J).
Return value:

If either I or J is a BOZ constant, it is first converted as if by the intrinsic function INT to an integer type with the kind type parameter of the other.

See also:

DSHIFTR — Combined right shift


9.91 DSHIFTR — Combined right shift

Description:

DSHIFTR(I, J, SHIFT) combines bits of I and J. The leftmost SHIFT bits of the result are the rightmost SHIFT bits of I, and the remaining bits are the leftmost bits of J.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = DSHIFTR(I, J, SHIFT)

Arguments:
IShall be of type INTEGER or a BOZ constant.
JShall be of type INTEGER or a BOZ constant. If both I and J have integer type, then they shall have the same kind type parameter. I and J shall not both be BOZ constants.
SHIFTShall be of type INTEGER. It shall be nonnegative. If I is not a BOZ constant, then SHIFT shall be less than or equal to BIT_SIZE(I); otherwise, SHIFT shall be less than or equal to BIT_SIZE(J).
Return value:

If either I or J is a BOZ constant, it is first converted as if by the intrinsic function INT to an integer type with the kind type parameter of the other.

See also:

DSHIFTL — Combined left shift


9.92 DTIME — Execution time subroutine (or function)

Description:

DTIME(VALUES, TIME) initially returns the number of seconds of runtime since the start of the process’s execution in TIME. VALUES returns the user and system components of this time in VALUES(1) and VALUES(2) respectively. TIME is equal to VALUES(1) + VALUES(2).

Subsequent invocations of DTIME return values accumulated since the previous invocation.

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wrap around) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

Please note, that this implementation is thread safe if used within OpenMP directives, i.e., its state will be consistent while called from multiple threads. However, if DTIME is called from multiple threads, the result is still the time since the last invocation. This may not give the intended results. If possible, use CPU_TIME instead.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

VALUES and TIME are INTENT(OUT) and provide the following:

VALUES(1):User time in seconds.
VALUES(2):System time in seconds.
TIME:Run time since start in seconds.
Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL DTIME(VALUES, TIME).
TIME = DTIME(VALUES), (not recommended).
Arguments:
VALUESThe type shall be REAL(4), DIMENSION(2).
TIMEThe type shall be REAL(4).
Return value:

Elapsed time in seconds since the last invocation or since the start of program execution if not called before.

Example:
program test_dtime
    integer(8) :: i, j
    real, dimension(2) :: tarray
    real :: result
    call dtime(tarray, result)
    print *, result
    print *, tarray(1)
    print *, tarray(2)   
    do i=1,100000000    ! Just a delay
        j = i * i - i
    end do
    call dtime(tarray, result)
    print *, result
    print *, tarray(1)
    print *, tarray(2)
end program test_dtime
See also:

CPU_TIME — CPU elapsed time in seconds


9.93 EOSHIFT — End-off shift elements of an array

Description:

EOSHIFT(ARRAY, SHIFT[, BOUNDARY, DIM]) performs an end-off shift on elements of ARRAY along the dimension of DIM. If DIM is omitted it is taken to be 1. DIM is a scalar of type INTEGER in the range of 1 \leq DIM \leq n) where n is the rank of ARRAY. If the rank of ARRAY is one, then all elements of ARRAY are shifted by SHIFT places. If rank is greater than one, then all complete rank one sections of ARRAY along the given dimension are shifted. Elements shifted out one end of each rank one section are dropped. If BOUNDARY is present then the corresponding value of from BOUNDARY is copied back in the other end. If BOUNDARY is not present then the following are copied in depending on the type of ARRAY.

Array TypeBoundary Value
Numeric0 of the type and kind of ARRAY.
Logical.FALSE..
Character(len)len blanks.
Standard:

Fortran 90 and later

Class:

Transformational function

Syntax:

RESULT = EOSHIFT(ARRAY, SHIFT [, BOUNDARY, DIM])

Arguments:
ARRAYMay be any type, not scalar.
SHIFTThe type shall be INTEGER.
BOUNDARYSame type as ARRAY.
DIMThe type shall be INTEGER.
Return value:

Returns an array of same type and rank as the ARRAY argument.

Example:
program test_eoshift
    integer, dimension(3,3) :: a
    a = reshape( (/ 1, 2, 3, 4, 5, 6, 7, 8, 9 /), (/ 3, 3 /))
    print '(3i3)', a(1,:)
    print '(3i3)', a(2,:)
    print '(3i3)', a(3,:)    
    a = EOSHIFT(a, SHIFT=(/1, 2, 1/), BOUNDARY=-5, DIM=2)
    print *
    print '(3i3)', a(1,:)
    print '(3i3)', a(2,:)
    print '(3i3)', a(3,:)
end program test_eoshift

9.94 EPSILON — Epsilon function

Description:

EPSILON(X) returns the smallest number E of the same kind as X such that 1 + E > 1.

Standard:

Fortran 90 and later

Class:

Inquiry function

Syntax:

RESULT = EPSILON(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of same type as the argument.

Example:
program test_epsilon
    real :: x = 3.143
    real(8) :: y = 2.33
    print *, EPSILON(x)
    print *, EPSILON(y)
end program test_epsilon

9.95 ERF — Error function

Description:

ERF(X) computes the error function of X.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = ERF(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type REAL, of the same kind as X and lies in the range -1 \leq erf (x) \leq 1 .

Example:
program test_erf
  real(8) :: x = 0.17_8
  x = erf(x)
end program test_erf
Specific names:
NameArgumentReturn typeStandard
DERF(X)REAL(8) XREAL(8)GNU extension

9.96 ERFC — Error function

Description:

ERFC(X) computes the complementary error function of X.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = ERFC(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type REAL and of the same kind as X. It lies in the range 0 \leq erfc (x) \leq 2 .

Example:
program test_erfc
  real(8) :: x = 0.17_8
  x = erfc(x)
end program test_erfc
Specific names:
NameArgumentReturn typeStandard
DERFC(X)REAL(8) XREAL(8)GNU extension

9.97 ERFC_SCALED — Error function

Description:

ERFC_SCALED(X) computes the exponentially-scaled complementary error function of X.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = ERFC_SCALED(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type REAL and of the same kind as X.

Example:
program test_erfc_scaled
  real(8) :: x = 0.17_8
  x = erfc_scaled(x)
end program test_erfc_scaled

9.98 ETIME — Execution time subroutine (or function)

Description:

ETIME(VALUES, TIME) returns the number of seconds of runtime since the start of the process’s execution in TIME. VALUES returns the user and system components of this time in VALUES(1) and VALUES(2) respectively. TIME is equal to VALUES(1) + VALUES(2).

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wrap around) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

VALUES and TIME are INTENT(OUT) and provide the following:

VALUES(1):User time in seconds.
VALUES(2):System time in seconds.
TIME:Run time since start in seconds.
Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL ETIME(VALUES, TIME).
TIME = ETIME(VALUES), (not recommended).
Arguments:
VALUESThe type shall be REAL(4), DIMENSION(2).
TIMEThe type shall be REAL(4).
Return value:

Elapsed time in seconds since the start of program execution.

Example:
program test_etime
    integer(8) :: i, j
    real, dimension(2) :: tarray
    real :: result
    call ETIME(tarray, result)
    print *, result
    print *, tarray(1)
    print *, tarray(2)   
    do i=1,100000000    ! Just a delay
        j = i * i - i
    end do
    call ETIME(tarray, result)
    print *, result
    print *, tarray(1)
    print *, tarray(2)
end program test_etime
See also:

CPU_TIME — CPU elapsed time in seconds


9.99 EVENT_QUERY — Query whether a coarray event has occurred

Description:

EVENT_QUERY assignes the number of events to COUNT which have been posted to the EVENT variable and not yet been removed by calling EVENT WAIT. When STAT is present and the invocation was successful, it is assigned the value 0. If it is present and the invocation has failed, it is assigned a positive value and COUNT is assigned the value -1.

Standard:

TS 18508 or later

Class:

subroutine

Syntax:

CALL EVENT_QUERY (EVENT, COUNT [, STAT])

Arguments:
EVENT(intent(IN)) Scalar of type EVENT_TYPE, defined in ISO_FORTRAN_ENV; shall not be coindexed.
COUNT(intent(out))Scalar integer with at least the precision of default integer.
STAT(optional) Scalar default-kind integer variable.
Example:
program atomic
  use iso_fortran_env
  implicit none
  type(event_type) :: event_value_has_been_set[*]
  integer :: cnt
  if (this_image() == 1) then
    call event_query (event_value_has_been_set, cnt)
    if (cnt > 0) write(*,*) "Value has been set"
  elseif (this_image() == 2) then
    event post (event_value_has_been_set[1])
  end if
end program atomic

9.100 EXECUTE_COMMAND_LINE — Execute a shell command

Description:

EXECUTE_COMMAND_LINE runs a shell command, synchronously or asynchronously.

The COMMAND argument is passed to the shell and executed (The shell is sh on Unix systems, and cmd.exe on Windows.). If WAIT is present and has the value false, the execution of the command is asynchronous if the system supports it; otherwise, the command is executed synchronously using the C library’s system call.

The three last arguments allow the user to get status information. After synchronous execution, EXITSTAT contains the integer exit code of the command, as returned by system. CMDSTAT is set to zero if the command line was executed (whatever its exit status was). CMDMSG is assigned an error message if an error has occurred.

Note that the system function need not be thread-safe. It is the responsibility of the user to ensure that system is not called concurrently.

For asynchronous execution on supported targets, the POSIX posix_spawn or fork functions are used. Also, a signal handler for the SIGCHLD signal is installed.

Standard:

Fortran 2008 and later

Class:

Subroutine

Syntax:

CALL EXECUTE_COMMAND_LINE(COMMAND [, WAIT, EXITSTAT, CMDSTAT, CMDMSG ])

Arguments:
COMMANDShall be a default CHARACTER scalar.
WAIT(Optional) Shall be a default LOGICAL scalar.
EXITSTAT(Optional) Shall be an INTEGER of the default kind.
CMDSTAT(Optional) Shall be an INTEGER of the default kind.
CMDMSG(Optional) Shall be an CHARACTER scalar of the default kind.
Example:
program test_exec
  integer :: i

  call execute_command_line ("external_prog.exe", exitstat=i)
  print *, "Exit status of external_prog.exe was ", i

  call execute_command_line ("reindex_files.exe", wait=.false.)
  print *, "Now reindexing files in the background"

end program test_exec
Note:

Because this intrinsic is implemented in terms of the system function call, its behavior with respect to signaling is processor dependent. In particular, on POSIX-compliant systems, the SIGINT and SIGQUIT signals will be ignored, and the SIGCHLD will be blocked. As such, if the parent process is terminated, the child process might not be terminated alongside.

See also:

SYSTEM — Execute a shell command


9.101 EXIT — Exit the program with status.

Description:

EXIT causes immediate termination of the program with status. If status is omitted it returns the canonical success for the system. All Fortran I/O units are closed.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL EXIT([STATUS])

Arguments:
STATUSShall be an INTEGER of the default kind.
Return value:

STATUS is passed to the parent process on exit.

Example:
program test_exit
  integer :: STATUS = 0
  print *, 'This program is going to exit.'
  call EXIT(STATUS)
end program test_exit
See also:

ABORT — Abort the program, KILL — Send a signal to a process


9.102 EXP — Exponential function

Description:

EXP(X) computes the base e exponential of X.

Standard:

Fortran 77 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = EXP(X)

Arguments:
XThe type shall be REAL or COMPLEX.
Return value:

The return value has same type and kind as X.

Example:
program test_exp
  real :: x = 1.0
  x = exp(x)
end program test_exp
Specific names:
NameArgumentReturn typeStandard
EXP(X)REAL(4) XREAL(4)Fortran 77 and later
DEXP(X)REAL(8) XREAL(8)Fortran 77 and later
CEXP(X)COMPLEX(4) XCOMPLEX(4)Fortran 77 and later
ZEXP(X)COMPLEX(8) XCOMPLEX(8)GNU extension
CDEXP(X)COMPLEX(8) XCOMPLEX(8)GNU extension

9.103 EXPONENT — Exponent function

Description:

EXPONENT(X) returns the value of the exponent part of X. If X is zero the value returned is zero.

Standard:

Fortran 90 and later

Class:

Elemental function

Syntax:

RESULT = EXPONENT(X)

Arguments:
XThe type shall be REAL.
Return value:

The return value is of type default INTEGER.

Example:
program test_exponent
  real :: x = 1.0
  integer :: i
  i = exponent(x)
  print *, i
  print *, exponent(0.0)
end program test_exponent

9.104 EXTENDS_TYPE_OF — Query dynamic type for extension

Description:

Query dynamic type for extension.

Standard:

Fortran 2003 and later

Class:

Inquiry function

Syntax:

RESULT = EXTENDS_TYPE_OF(A, MOLD)

Arguments:
AShall be an object of extensible declared type or unlimited polymorphic.
MOLDShall be an object of extensible declared type or unlimited polymorphic.
Return value:

The return value is a scalar of type default logical. It is true if and only if the dynamic type of A is an extension type of the dynamic type of MOLD.

See also:

SAME_TYPE_AS — Query dynamic types for equality


9.105 FDATE — Get the current time as a string

Description:

FDATE(DATE) returns the current date (using the same format as CTIME — Convert a time into a string) in DATE. It is equivalent to CALL CTIME(DATE, TIME()).

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL FDATE(DATE).
DATE = FDATE().
Arguments:
DATEThe type shall be of type CHARACTER of the default kind. It is an INTENT(OUT) argument. If the length of this variable is too short for the date and time string to fit completely, it will be blank on procedure return.
Return value:

The current date and time as a string.

Example:
program test_fdate
    integer(8) :: i, j
    character(len=30) :: date
    call fdate(date)
    print *, 'Program started on ', date
    do i = 1, 100000000 ! Just a delay
        j = i * i - i
    end do
    call fdate(date)
    print *, 'Program ended on ', date
end program test_fdate
See also:

DATE_AND_TIME — Date and time subroutine, CTIME — Convert a time into a string


9.106 FGET — Read a single character in stream mode from stdin

Description:

Read a single character in stream mode from stdin by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Note that the FGET intrinsic is provided for backwards compatibility with g77. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL FGET(C [, STATUS])
STATUS = FGET(C)
Arguments:
CThe type shall be CHARACTER and of default kind.
STATUS(Optional) status flag of type INTEGER. Returns 0 on success, -1 on end-of-file, and a system specific positive error code otherwise.
Example:
PROGRAM test_fget
  INTEGER, PARAMETER :: strlen = 100
  INTEGER :: status, i = 1
  CHARACTER(len=strlen) :: str = ""

  WRITE (*,*) 'Enter text:'
  DO
    CALL fget(str(i:i), status)
    if (status /= 0 .OR. i > strlen) exit
    i = i + 1
  END DO
  WRITE (*,*) TRIM(str)
END PROGRAM
See also:

FGETC — Read a single character in stream mode, FPUT — Write a single character in stream mode to stdout, FPUTC — Write a single character in stream mode


9.107 FGETC — Read a single character in stream mode

Description:

Read a single character in stream mode by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Note that the FGET intrinsic is provided for backwards compatibility with g77. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL FGETC(UNIT, C [, STATUS])
STATUS = FGETC(UNIT, C)
Arguments:
UNITThe type shall be INTEGER.
CThe type shall be CHARACTER and of default kind.
STATUS(Optional) status flag of type INTEGER. Returns 0 on success, -1 on end-of-file and a system specific positive error code otherwise.
Example:
PROGRAM test_fgetc
  INTEGER :: fd = 42, status
  CHARACTER :: c

  OPEN(UNIT=fd, FILE="/etc/passwd", ACTION="READ", STATUS = "OLD")
  DO
    CALL fgetc(fd, c, status)
    IF (status /= 0) EXIT
    call fput(c)
  END DO
  CLOSE(UNIT=fd)
END PROGRAM
See also:

FGET — Read a single character in stream mode from stdin, FPUT — Write a single character in stream mode to stdout, FPUTC — Write a single character in stream mode


9.108 FINDLOC — Search an array for a value

Description:

Determines the location of the element in the array with the value given in the VALUE argument, or, if the DIM argument is supplied, determines the locations of the elements equal to the VALUE argument element along each row of the array in the DIM direction. If MASK is present, only the elements for which MASK is .TRUE. are considered. If more than one element in the array has the value VALUE, the location returned is that of the first such element in array element order if the BACK is not present or if it is .FALSE.. If BACK is true, the location returned is that of the last such element. If the array has zero size, or all of the elements of MASK are .FALSE., then the result is an array of zeroes. Similarly, if DIM is supplied and all of the elements of MASK along a given row are zero, the result value for that row is zero.

Standard:

Fortran 2008 and later.

Class:

Transformational function

Syntax:
RESULT = FINDLOC(ARRAY, VALUE, DIM [, MASK] [,KIND] [,BACK])
RESULT = FINDLOC(ARRAY, VALUE, [, MASK] [,KIND] [,BACK])
Arguments:
ARRAYShall be an array of intrinsic type.
VALUEA scalar of intrinsic type which is in type conformance with ARRAY.
DIM(Optional) Shall be a scalar of type INTEGER, with a value between one and the rank of ARRAY, inclusive. It may not be an optional dummy argument.
MASK(Optional) Shall be of type LOGICAL, and conformable with ARRAY.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
BACK(Optional) A scalar of type LOGICAL.
Return value:

If DIM is absent, the result is a rank-one array with a length equal to the rank of ARRAY. If DIM is present, the result is an array with a rank one less than the rank of ARRAY, and a size corresponding to the size of ARRAY with the DIM dimension removed. If DIM is present and ARRAY has a rank of one, the result is a scalar. If the optional argument KIND is present, the result is an integer of kind KIND, otherwise it is of default kind.

See also:

MAXLOC — Location of the maximum value within an array, MINLOC — Location of the minimum value within an array


9.109 FLOOR — Integer floor function

Description:

FLOOR(A) returns the greatest integer less than or equal to X.

Standard:

Fortran 95 and later

Class:

Elemental function

Syntax:

RESULT = FLOOR(A [, KIND])

Arguments:
AThe type shall be REAL.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER(KIND) if KIND is present and of default-kind INTEGER otherwise.

Example:
program test_floor
    real :: x = 63.29
    real :: y = -63.59
    print *, floor(x) ! returns 63
    print *, floor(y) ! returns -64
end program test_floor
See also:

CEILING — Integer ceiling function, NINT — Nearest whole number


9.110 FLUSH — Flush I/O unit(s)

Description:

Flushes Fortran unit(s) currently open for output. Without the optional argument, all units are flushed, otherwise just the unit specified.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL FLUSH(UNIT)

Arguments:
UNIT(Optional) The type shall be INTEGER.
Note:

Beginning with the Fortran 2003 standard, there is a FLUSH statement that should be preferred over the FLUSH intrinsic.

The FLUSH intrinsic and the Fortran 2003 FLUSH statement have identical effect: they flush the runtime library’s I/O buffer so that the data becomes visible to other processes. This does not guarantee that the data is committed to disk.

On POSIX systems, you can request that all data is transferred to the storage device by calling the fsync function, with the POSIX file descriptor of the I/O unit as argument (retrieved with GNU intrinsic FNUM). The following example shows how:

  ! Declare the interface for POSIX fsync function
  interface
    function fsync (fd) bind(c,name="fsync")
    use iso_c_binding, only: c_int
      integer(c_int), value :: fd
      integer(c_int) :: fsync
    end function fsync
  end interface

  ! Variable declaration
  integer :: ret

  ! Opening unit 10
  open (10,file="foo")

  ! ...
  ! Perform I/O on unit 10
  ! ...

  ! Flush and sync
  flush(10)
  ret = fsync(fnum(10))

  ! Handle possible error
  if (ret /= 0) stop "Error calling FSYNC"

9.111 FNUM — File number function

Description:

FNUM(UNIT) returns the POSIX file descriptor number corresponding to the open Fortran I/O unit UNIT.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = FNUM(UNIT)

Arguments:
UNITThe type shall be INTEGER.
Return value:

The return value is of type INTEGER

Example:
program test_fnum
  integer :: i
  open (unit=10, status = "scratch")
  i = fnum(10)
  print *, i
  close (10)
end program test_fnum

9.112 FPUT — Write a single character in stream mode to stdout

Description:

Write a single character in stream mode to stdout by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Note that the FGET intrinsic is provided for backwards compatibility with g77. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL FPUT(C [, STATUS])
STATUS = FPUT(C)
Arguments:
CThe type shall be CHARACTER and of default kind.
STATUS(Optional) status flag of type INTEGER. Returns 0 on success, -1 on end-of-file and a system specific positive error code otherwise.
Example:
PROGRAM test_fput
  CHARACTER(len=10) :: str = "gfortran"
  INTEGER :: i
  DO i = 1, len_trim(str)
    CALL fput(str(i:i))
  END DO
END PROGRAM
See also:

FPUTC — Write a single character in stream mode, FGET — Read a single character in stream mode from stdin, FGETC — Read a single character in stream mode


9.113 FPUTC — Write a single character in stream mode

Description:

Write a single character in stream mode by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Note that the FGET intrinsic is provided for backwards compatibility with g77. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL FPUTC(UNIT, C [, STATUS])
STATUS = FPUTC(UNIT, C)
Arguments:
UNITThe type shall be INTEGER.
CThe type shall be CHARACTER and of default kind.
STATUS(Optional) status flag of type INTEGER. Returns 0 on success, -1 on end-of-file and a system specific positive error code otherwise.
Example:
PROGRAM test_fputc
  CHARACTER(len=10) :: str = "gfortran"
  INTEGER :: fd = 42, i

  OPEN(UNIT = fd, FILE = "out", ACTION = "WRITE", STATUS="NEW")
  DO i = 1, len_trim(str)
    CALL fputc(fd, str(i:i))
  END DO
  CLOSE(fd)
END PROGRAM
See also:

FPUT — Write a single character in stream mode to stdout, FGET — Read a single character in stream mode from stdin, FGETC — Read a single character in stream mode


9.114 FRACTION — Fractional part of the model representation

Description:

FRACTION(X) returns the fractional part of the model representation of X.

Standard:

Fortran 90 and later

Class:

Elemental function

Syntax:

Y = FRACTION(X)

Arguments:
XThe type of the argument shall be a REAL.
Return value:

The return value is of the same type and kind as the argument. The fractional part of the model representation of X is returned; it is X * RADIX(X)**(-EXPONENT(X)).

Example:
program test_fraction
  real :: x
  x = 178.1387e-4
  print *, fraction(x), x * radix(x)**(-exponent(x))
end program test_fraction

9.115 FREE — Frees memory

Description:

Frees memory previously allocated by MALLOC. The FREE intrinsic is an extension intended to be used with Cray pointers, and is provided in GNU Fortran to allow user to compile legacy code. For new code using Fortran 95 pointers, the memory de-allocation intrinsic is DEALLOCATE.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL FREE(PTR)

Arguments:
PTRThe type shall be INTEGER. It represents the location of the memory that should be de-allocated.
Return value:

None

Example:

See MALLOC for an example.

See also:

MALLOC — Allocate dynamic memory


9.116 FSEEK — Low level file positioning subroutine

Description:

Moves UNIT to the specified OFFSET. If WHENCE is set to 0, the OFFSET is taken as an absolute value SEEK_SET, if set to 1, OFFSET is taken to be relative to the current position SEEK_CUR, and if set to 2 relative to the end of the file SEEK_END. On error, STATUS is set to a nonzero value. If STATUS the seek fails silently.

This intrinsic routine is not fully backwards compatible with g77. In g77, the FSEEK takes a statement label instead of a STATUS variable. If FSEEK is used in old code, change

  CALL FSEEK(UNIT, OFFSET, WHENCE, *label)

to

  INTEGER :: status
  CALL FSEEK(UNIT, OFFSET, WHENCE, status)
  IF (status /= 0) GOTO label

Please note that GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL FSEEK(UNIT, OFFSET, WHENCE[, STATUS])

Arguments:
UNITShall be a scalar of type INTEGER.
OFFSETShall be a scalar of type INTEGER.
WHENCEShall be a scalar of type INTEGER. Its value shall be either 0, 1 or 2.
STATUS(Optional) shall be a scalar of type INTEGER(4).
Example:
PROGRAM test_fseek
  INTEGER, PARAMETER :: SEEK_SET = 0, SEEK_CUR = 1, SEEK_END = 2
  INTEGER :: fd, offset, ierr

  ierr   = 0
  offset = 5
  fd     = 10

  OPEN(UNIT=fd, FILE="fseek.test")
  CALL FSEEK(fd, offset, SEEK_SET, ierr)  ! move to OFFSET
  print *, FTELL(fd), ierr

  CALL FSEEK(fd, 0, SEEK_END, ierr)       ! move to end
  print *, FTELL(fd), ierr

  CALL FSEEK(fd, 0, SEEK_SET, ierr)       ! move to beginning
  print *, FTELL(fd), ierr

  CLOSE(UNIT=fd)
END PROGRAM
See also:

FTELL — Current stream position


9.117 FSTAT — Get file status

Description:

FSTAT is identical to STAT — Get file status, except that information about an already opened file is obtained.

The elements in VALUES are the same as described by STAT — Get file status.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL FSTAT(UNIT, VALUES [, STATUS])
STATUS = FSTAT(UNIT, VALUES)
Arguments:
UNITAn open I/O unit number of type INTEGER.
VALUESThe type shall be INTEGER(4), DIMENSION(13).
STATUS(Optional) status flag of type INTEGER(4). Returns 0 on success and a system specific error code otherwise.
Example:

See STAT — Get file status for an example.

See also:

To stat a link: LSTAT — Get file status To stat a file: STAT — Get file status


9.118 FTELL — Current stream position

Description:

Retrieves the current position within an open file.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL FTELL(UNIT, OFFSET)
OFFSET = FTELL(UNIT)
Arguments:
OFFSETShall of type INTEGER.
UNITShall of type INTEGER.
Return value:

In either syntax, OFFSET is set to the current offset of unit number UNIT, or to -1 if the unit is not currently open.

Example:
PROGRAM test_ftell
  INTEGER :: i
  OPEN(10, FILE="temp.dat")
  CALL ftell(10,i)
  WRITE(*,*) i
END PROGRAM
See also:

FSEEK — Low level file positioning subroutine


9.119 GAMMA — Gamma function

Description:

GAMMA(X) computes Gamma (\Gamma) of X. For positive, integer values of X the Gamma function simplifies to the factorial function \Gamma(x)=(x-1)!.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

X = GAMMA(X)

Arguments:
XShall be of type REAL and neither zero nor a negative integer.
Return value:

The return value is of type REAL of the same kind as X.

Example:
program test_gamma
  real :: x = 1.0
  x = gamma(x) ! returns 1.0
end program test_gamma
Specific names:
NameArgumentReturn typeStandard
DGAMMA(X)REAL(8) XREAL(8)GNU extension
See also:

Logarithm of the Gamma function: LOG_GAMMA — Logarithm of the Gamma function


9.120 GERROR — Get last system error message

Description:

Returns the system error message corresponding to the last system error. This resembles the functionality of strerror(3) in C.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL GERROR(RESULT)

Arguments:
RESULTShall be of type CHARACTER and of default kind.
Example:
PROGRAM test_gerror
  CHARACTER(len=100) :: msg
  CALL gerror(msg)
  WRITE(*,*) msg
END PROGRAM
See also:

IERRNO — Get the last system error number, PERROR — Print system error message


9.121 GETARG — Get command line arguments

Description:

Retrieve the POS-th argument that was passed on the command line when the containing program was invoked.

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the GET_COMMAND_ARGUMENT — Get command line arguments intrinsic defined by the Fortran 2003 standard.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL GETARG(POS, VALUE)

Arguments:
POSShall be of type INTEGER and not wider than the default integer kind; POS \geq 0
VALUEShall be of type CHARACTER and of default kind.
Return value:

After GETARG returns, the VALUE argument holds the POSth command line argument. If VALUE cannot hold the argument, it is truncated to fit the length of VALUE. If there are less than POS arguments specified at the command line, VALUE will be filled with blanks. If POS = 0, VALUE is set to the name of the program (on systems that support this feature).

Example:
PROGRAM test_getarg
  INTEGER :: i
  CHARACTER(len=32) :: arg

  DO i = 1, iargc()
    CALL getarg(i, arg)
    WRITE (*,*) arg
  END DO
END PROGRAM
See also:

GNU Fortran 77 compatibility function: IARGC — Get the number of command line arguments Fortran 2003 functions and subroutines: GET_COMMAND — Get the entire command line, GET_COMMAND_ARGUMENT — Get command line arguments, COMMAND_ARGUMENT_COUNT — Get number of command line arguments


9.122 GET_COMMAND — Get the entire command line

Description:

Retrieve the entire command line that was used to invoke the program.

Standard:

Fortran 2003 and later

Class:

Subroutine

Syntax:

CALL GET_COMMAND([COMMAND, LENGTH, STATUS])

Arguments:
COMMAND(Optional) shall be of type CHARACTER and of default kind.
LENGTH(Optional) Shall be of type INTEGER and of default kind.
STATUS(Optional) Shall be of type INTEGER and of default kind.
Return value:

If COMMAND is present, stores the entire command line that was used to invoke the program in COMMAND. If LENGTH is present, it is assigned the length of the command line. If STATUS is present, it is assigned 0 upon success of the command, -1 if COMMAND is too short to store the command line, or a positive value in case of an error.

Example:
PROGRAM test_get_command
  CHARACTER(len=255) :: cmd
  CALL get_command(cmd)
  WRITE (*,*) TRIM(cmd)
END PROGRAM
See also:

GET_COMMAND_ARGUMENT — Get command line arguments, COMMAND_ARGUMENT_COUNT — Get number of command line arguments


9.123 GET_COMMAND_ARGUMENT — Get command line arguments

Description:

Retrieve the NUMBER-th argument that was passed on the command line when the containing program was invoked.

Standard:

Fortran 2003 and later

Class:

Subroutine

Syntax:

CALL GET_COMMAND_ARGUMENT(NUMBER [, VALUE, LENGTH, STATUS])

Arguments:
NUMBERShall be a scalar of type INTEGER and of default kind, NUMBER \geq 0
VALUE(Optional) Shall be a scalar of type CHARACTER and of default kind.
LENGTH(Optional) Shall be a scalar of type INTEGER and of default kind.
STATUS(Optional) Shall be a scalar of type INTEGER and of default kind.
Return value:

After GET_COMMAND_ARGUMENT returns, the VALUE argument holds the NUMBER-th command line argument. If VALUE cannot hold the argument, it is truncated to fit the length of VALUE. If there are less than NUMBER arguments specified at the command line, VALUE will be filled with blanks. If NUMBER = 0, VALUE is set to the name of the program (on systems that support this feature). The LENGTH argument contains the length of the NUMBER-th command line argument. If the argument retrieval fails, STATUS is a positive number; if VALUE contains a truncated command line argument, STATUS is -1; and otherwise the STATUS is zero.

Example:
PROGRAM test_get_command_argument
  INTEGER :: i
  CHARACTER(len=32) :: arg

  i = 0
  DO
    CALL get_command_argument(i, arg)
    IF (LEN_TRIM(arg) == 0) EXIT

    WRITE (*,*) TRIM(arg)
    i = i+1
  END DO
END PROGRAM
See also:

GET_COMMAND — Get the entire command line, COMMAND_ARGUMENT_COUNT — Get number of command line arguments


9.124 GETCWD — Get current working directory

Description:

Get current working directory.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL GETCWD(C [, STATUS])
STATUS = GETCWD(C)
Arguments:
CThe type shall be CHARACTER and of default kind.
STATUS(Optional) status flag. Returns 0 on success, a system specific and nonzero error code otherwise.
Example:
PROGRAM test_getcwd
  CHARACTER(len=255) :: cwd
  CALL getcwd(cwd)
  WRITE(*,*) TRIM(cwd)
END PROGRAM
See also:

CHDIR — Change working directory


9.125 GETENV — Get an environmental variable

Description:

Get the VALUE of the environmental variable NAME.

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the GET_ENVIRONMENT_VARIABLE — Get an environmental variable intrinsic defined by the Fortran 2003 standard.

Note that GETENV need not be thread-safe. It is the responsibility of the user to ensure that the environment is not being updated concurrently with a call to the GETENV intrinsic.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL GETENV(NAME, VALUE)

Arguments:
NAMEShall be of type CHARACTER and of default kind.
VALUEShall be of type CHARACTER and of default kind.
Return value:

Stores the value of NAME in VALUE. If VALUE is not large enough to hold the data, it is truncated. If NAME is not set, VALUE will be filled with blanks.

Example:
PROGRAM test_getenv
  CHARACTER(len=255) :: homedir
  CALL getenv("HOME", homedir)
  WRITE (*,*) TRIM(homedir)
END PROGRAM
See also:

GET_ENVIRONMENT_VARIABLE — Get an environmental variable


9.126 GET_ENVIRONMENT_VARIABLE — Get an environmental variable

Description:

Get the VALUE of the environmental variable NAME.

Note that GET_ENVIRONMENT_VARIABLE need not be thread-safe. It is the responsibility of the user to ensure that the environment is not being updated concurrently with a call to the GET_ENVIRONMENT_VARIABLE intrinsic.

Standard:

Fortran 2003 and later

Class:

Subroutine

Syntax:

CALL GET_ENVIRONMENT_VARIABLE(NAME[, VALUE, LENGTH, STATUS, TRIM_NAME)

Arguments:
NAMEShall be a scalar of type CHARACTER and of default kind.
VALUE(Optional) Shall be a scalar of type CHARACTER and of default kind.
LENGTH(Optional) Shall be a scalar of type INTEGER and of default kind.
STATUS(Optional) Shall be a scalar of type INTEGER and of default kind.
TRIM_NAME(Optional) Shall be a scalar of type LOGICAL and of default kind.
Return value:

Stores the value of NAME in VALUE. If VALUE is not large enough to hold the data, it is truncated. If NAME is not set, VALUE will be filled with blanks. Argument LENGTH contains the length needed for storing the environment variable NAME or zero if it is not present. STATUS is -1 if VALUE is present but too short for the environment variable; it is 1 if the environment variable does not exist and 2 if the processor does not support environment variables; in all other cases STATUS is zero. If TRIM_NAME is present with the value .FALSE., the trailing blanks in NAME are significant; otherwise they are not part of the environment variable name.

Example:
PROGRAM test_getenv
  CHARACTER(len=255) :: homedir
  CALL get_environment_variable("HOME", homedir)
  WRITE (*,*) TRIM(homedir)
END PROGRAM

9.127 GETGID — Group ID function

Description:

Returns the numerical group ID of the current process.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = GETGID()

Return value:

The return value of GETGID is an INTEGER of the default kind.

Example:

See GETPID for an example.

See also:

GETPID — Process ID function, GETUID — User ID function


9.128 GETLOG — Get login name

Description:

Gets the username under which the program is running.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL GETLOG(C)

Arguments:
CShall be of type CHARACTER and of default kind.
Return value:

Stores the current user name in C. (On systems where POSIX functions geteuid and getpwuid are not available, and the getlogin function is not implemented either, this will return a blank string.)

Example:
PROGRAM TEST_GETLOG
  CHARACTER(32) :: login
  CALL GETLOG(login)
  WRITE(*,*) login
END PROGRAM
See also:

GETUID — User ID function


9.129 GETPID — Process ID function

Description:

Returns the numerical process identifier of the current process.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = GETPID()

Return value:

The return value of GETPID is an INTEGER of the default kind.

Example:
program info
  print *, "The current process ID is ", getpid()
  print *, "Your numerical user ID is ", getuid()
  print *, "Your numerical group ID is ", getgid()
end program info
See also:

GETGID — Group ID function, GETUID — User ID function


9.130 GETUID — User ID function

Description:

Returns the numerical user ID of the current process.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = GETUID()

Return value:

The return value of GETUID is an INTEGER of the default kind.

Example:

See GETPID for an example.

See also:

GETPID — Process ID function, GETLOG — Get login name


9.131 GMTIME — Convert time to GMT info

Description:

Given a system time value TIME (as provided by the TIME — Time function intrinsic), fills VALUES with values extracted from it appropriate to the UTC time zone (Universal Coordinated Time, also known in some countries as GMT, Greenwich Mean Time), using gmtime(3).

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the DATE_AND_TIME — Date and time subroutine intrinsic defined by the Fortran 95 standard.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL GMTIME(TIME, VALUES)

Arguments:
TIMEAn INTEGER scalar expression corresponding to a system time, with INTENT(IN).
VALUESA default INTEGER array with 9 elements, with INTENT(OUT).
Return value:

The elements of VALUES are assigned as follows:

  1. Seconds after the minute, range 0–59 or 0–61 to allow for leap seconds
  2. Minutes after the hour, range 0–59
  3. Hours past midnight, range 0–23
  4. Day of month, range 1–31
  5. Number of months since January, range 0–11
  6. Years since 1900
  7. Number of days since Sunday, range 0–6
  8. Days since January 1, range 0–365
  9. Daylight savings indicator: positive if daylight savings is in effect, zero if not, and negative if the information is not available.
See also:

DATE_AND_TIME — Date and time subroutine, CTIME — Convert a time into a string, LTIME — Convert time to local time info, TIME — Time function, TIME8 — Time function (64-bit)


9.132 HOSTNM — Get system host name

Description:

Retrieves the host name of the system on which the program is running.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL HOSTNM(C [, STATUS])
STATUS = HOSTNM(NAME)
Arguments:
CShall of type CHARACTER and of default kind.
STATUS(Optional) status flag of type INTEGER. Returns 0 on success, or a system specific error code otherwise.
Return value:

In either syntax, NAME is set to the current hostname if it can be obtained, or to a blank string otherwise.


9.133 HUGE — Largest number of a kind

Description:

HUGE(X) returns the largest number that is not an infinity in the model of the type of X.

Standard:

Fortran 90 and later

Class:

Inquiry function

Syntax:

RESULT = HUGE(X)

Arguments:
XShall be of type REAL or INTEGER.
Return value:

The return value is of the same type and kind as X

Example:
program test_huge_tiny
  print *, huge(0), huge(0.0), huge(0.0d0)
  print *, tiny(0.0), tiny(0.0d0)
end program test_huge_tiny

9.134 HYPOT — Euclidean distance function

Description:

HYPOT(X,Y) is the Euclidean distance function. It is equal to \sqrt{X^2 + Y^2}, without undue underflow or overflow.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = HYPOT(X, Y)

Arguments:
XThe type shall be REAL.
YThe type and kind type parameter shall be the same as X.
Return value:

The return value has the same type and kind type parameter as X.

Example:
program test_hypot
  real(4) :: x = 1.e0_4, y = 0.5e0_4
  x = hypot(x,y)
end program test_hypot

9.135 IACHAR — Code in ASCII collating sequence

Description:

IACHAR(C) returns the code for the ASCII character in the first character position of C.

Standard:

Fortran 95 and later, with KIND argument Fortran 2003 and later

Class:

Elemental function

Syntax:

RESULT = IACHAR(C [, KIND])

Arguments:
CShall be a scalar CHARACTER, with INTENT(IN)
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER and of kind KIND. If KIND is absent, the return value is of default integer kind.

Example:
program test_iachar
  integer i
  i = iachar(' ')
end program test_iachar
Note:

See ICHAR — Character-to-integer conversion function for a discussion of converting between numerical values and formatted string representations.

See also:

ACHAR — Character in ASCII collating sequence, CHAR — Character conversion function, ICHAR — Character-to-integer conversion function


9.136 IALL — Bitwise AND of array elements

Description:

Reduces with bitwise AND the elements of ARRAY along dimension DIM if the corresponding element in MASK is TRUE.

Standard:

Fortran 2008 and later

Class:

Transformational function

Syntax:
RESULT = IALL(ARRAY[, MASK])
RESULT = IALL(ARRAY, DIM[, MASK])
Arguments:
ARRAYShall be an array of type INTEGER
DIM(Optional) shall be a scalar of type INTEGER with a value in the range from 1 to n, where n equals the rank of ARRAY.
MASK(Optional) shall be of type LOGICAL and either be a scalar or an array of the same shape as ARRAY.
Return value:

The result is of the same type as ARRAY.

If DIM is absent, a scalar with the bitwise ALL of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:
PROGRAM test_iall
  INTEGER(1) :: a(2)

  a(1) = b'00100100'
  a(2) = b'01101010'

  ! prints 00100000
  PRINT '(b8.8)', IALL(a)
END PROGRAM
See also:

IANY — Bitwise OR of array elements, IPARITY — Bitwise XOR of array elements, IAND — Bitwise logical and


9.137 IAND — Bitwise logical and

Description:

Bitwise logical AND.

Standard:

Fortran 90 and later, with boz-literal-constant Fortran 2008 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = IAND(I, J)

Arguments:
IThe type shall be INTEGER or a boz-literal-constant.
JThe type shall be INTEGER with the same kind type parameter as I or a boz-literal-constant. I and J shall not both be boz-literal-constants.
Return value:

The return type is INTEGER with the kind type parameter of the arguments. A boz-literal-constant is converted to an INTEGER with the kind type parameter of the other argument as-if a call to INT — Convert to integer type occurred.

Example:
PROGRAM test_iand
  INTEGER :: a, b
  DATA a / Z'F' /, b / Z'3' /
  WRITE (*,*) IAND(a, b)
END PROGRAM
Specific names:
NameArgumentReturn typeStandard
IAND(A)INTEGER AINTEGERFortran 90 and later
BIAND(A)INTEGER(1) AINTEGER(1)GNU extension
IIAND(A)INTEGER(2) AINTEGER(2)GNU extension
JIAND(A)INTEGER(4) AINTEGER(4)GNU extension
KIAND(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

IOR — Bitwise logical or, IEOR — Bitwise logical exclusive or, IBITS — Bit extraction, IBSET — Set bit, IBCLR — Clear bit, NOT — Logical negation


9.138 IANY — Bitwise OR of array elements

Description:

Reduces with bitwise OR (inclusive or) the elements of ARRAY along dimension DIM if the corresponding element in MASK is TRUE.

Standard:

Fortran 2008 and later

Class:

Transformational function

Syntax:
RESULT = IANY(ARRAY[, MASK])
RESULT = IANY(ARRAY, DIM[, MASK])
Arguments:
ARRAYShall be an array of type INTEGER
DIM(Optional) shall be a scalar of type INTEGER with a value in the range from 1 to n, where n equals the rank of ARRAY.
MASK(Optional) shall be of type LOGICAL and either be a scalar or an array of the same shape as ARRAY.
Return value:

The result is of the same type as ARRAY.

If DIM is absent, a scalar with the bitwise OR of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:
PROGRAM test_iany
  INTEGER(1) :: a(2)

  a(1) = b'00100100'
  a(2) = b'01101010'

  ! prints 01101110
  PRINT '(b8.8)', IANY(a)
END PROGRAM
See also:

IPARITY — Bitwise XOR of array elements, IALL — Bitwise AND of array elements, IOR — Bitwise logical or


9.139 IARGC — Get the number of command line arguments

Description:

IARGC returns the number of arguments passed on the command line when the containing program was invoked.

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the COMMAND_ARGUMENT_COUNT — Get number of command line arguments intrinsic defined by the Fortran 2003 standard.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = IARGC()

Arguments:

None

Return value:

The number of command line arguments, type INTEGER(4).

Example:

See GETARG — Get command line arguments

See also:

GNU Fortran 77 compatibility subroutine: GETARG — Get command line arguments Fortran 2003 functions and subroutines: GET_COMMAND — Get the entire command line, GET_COMMAND_ARGUMENT — Get command line arguments, COMMAND_ARGUMENT_COUNT — Get number of command line arguments


9.140 IBCLR — Clear bit

Description:

IBCLR returns the value of I with the bit at position POS set to zero.

Standard:

Fortran 90 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = IBCLR(I, POS)

Arguments:
IThe type shall be INTEGER.
POSThe type shall be INTEGER.
Return value:

The return value is of type INTEGER and of the same kind as I.

Specific names:
NameArgumentReturn typeStandard
IBCLR(A)INTEGER AINTEGERFortran 90 and later
BBCLR(A)INTEGER(1) AINTEGER(1)GNU extension
IIBCLR(A)INTEGER(2) AINTEGER(2)GNU extension
JIBCLR(A)INTEGER(4) AINTEGER(4)GNU extension
KIBCLR(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

IBITS — Bit extraction, IBSET — Set bit, IAND — Bitwise logical and, IOR — Bitwise logical or, IEOR — Bitwise logical exclusive or, MVBITS — Move bits from one integer to another


9.141 IBITS — Bit extraction

Description:

IBITS extracts a field of length LEN from I, starting from bit position POS and extending left for LEN bits. The result is right-justified and the remaining bits are zeroed. The value of POS+LEN must be less than or equal to the value BIT_SIZE(I).

Standard:

Fortran 90 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = IBITS(I, POS, LEN)

Arguments:
IThe type shall be INTEGER.
POSThe type shall be INTEGER.
LENThe type shall be INTEGER.
Return value:

The return value is of type INTEGER and of the same kind as I.

Specific names:
NameArgumentReturn typeStandard
IBITS(A)INTEGER AINTEGERFortran 90 and later
BBITS(A)INTEGER(1) AINTEGER(1)GNU extension
IIBITS(A)INTEGER(2) AINTEGER(2)GNU extension
JIBITS(A)INTEGER(4) AINTEGER(4)GNU extension
KIBITS(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

BIT_SIZE — Bit size inquiry function, IBCLR — Clear bit, IBSET — Set bit, IAND — Bitwise logical and, IOR — Bitwise logical or, IEOR — Bitwise logical exclusive or


9.142 IBSET — Set bit

Description:

IBSET returns the value of I with the bit at position POS set to one.

Standard:

Fortran 90 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = IBSET(I, POS)

Arguments:
IThe type shall be INTEGER.
POSThe type shall be INTEGER.
Return value:

The return value is of type INTEGER and of the same kind as I.

Specific names:
NameArgumentReturn typeStandard
IBSET(A)INTEGER AINTEGERFortran 90 and later
BBSET(A)INTEGER(1) AINTEGER(1)GNU extension
IIBSET(A)INTEGER(2) AINTEGER(2)GNU extension
JIBSET(A)INTEGER(4) AINTEGER(4)GNU extension
KIBSET(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

IBCLR — Clear bit, IBITS — Bit extraction, IAND — Bitwise logical and, IOR — Bitwise logical or, IEOR — Bitwise logical exclusive or, MVBITS — Move bits from one integer to another


9.143 ICHAR — Character-to-integer conversion function

Description:

ICHAR(C) returns the code for the character in the first character position of C in the system’s native character set. The correspondence between characters and their codes is not necessarily the same across different GNU Fortran implementations.

Standard:

Fortran 77 and later, with KIND argument Fortran 2003 and later

Class:

Elemental function

Syntax:

RESULT = ICHAR(C [, KIND])

Arguments:
CShall be a scalar CHARACTER, with INTENT(IN)
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER and of kind KIND. If KIND is absent, the return value is of default integer kind.

Example:
program test_ichar
  integer i
  i = ichar(' ')
end program test_ichar
Specific names:
NameArgumentReturn typeStandard
ICHAR(C)CHARACTER CINTEGER(4)Fortran 77 and later
Note:

No intrinsic exists to convert between a numeric value and a formatted character string representation – for instance, given the CHARACTER value '154', obtaining an INTEGER or REAL value with the value 154, or vice versa. Instead, this functionality is provided by internal-file I/O, as in the following example:

program read_val
  integer value
  character(len=10) string, string2
  string = '154'
  
  ! Convert a string to a numeric value
  read (string,'(I10)') value
  print *, value
  
  ! Convert a value to a formatted string
  write (string2,'(I10)') value
  print *, string2
end program read_val
See also:

ACHAR — Character in ASCII collating sequence, CHAR — Character conversion function, IACHAR — Code in ASCII collating sequence


9.144 IDATE — Get current local time subroutine (day/month/year)

Description:

IDATE(VALUES) Fills VALUES with the numerical values at the current local time. The day (in the range 1-31), month (in the range 1-12), and year appear in elements 1, 2, and 3 of VALUES, respectively. The year has four significant digits.

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the DATE_AND_TIME — Date and time subroutine intrinsic defined by the Fortran 95 standard.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL IDATE(VALUES)

Arguments:
VALUESThe type shall be INTEGER, DIMENSION(3) and the kind shall be the default integer kind.
Return value:

Does not return anything.

Example:
program test_idate
  integer, dimension(3) :: tarray
  call idate(tarray)
  print *, tarray(1)
  print *, tarray(2)
  print *, tarray(3)
end program test_idate
See also:

DATE_AND_TIME — Date and time subroutine


9.145 IEOR — Bitwise logical exclusive or

Description:

IEOR returns the bitwise Boolean exclusive-OR of I and J.

Standard:

Fortran 90 and later, with boz-literal-constant Fortran 2008 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = IEOR(I, J)

Arguments:
IThe type shall be INTEGER or a boz-literal-constant.
JThe type shall be INTEGER with the same kind type parameter as I or a boz-literal-constant. I and J shall not both be boz-literal-constants.
Return value:

The return type is INTEGER with the kind type parameter of the arguments. A boz-literal-constant is converted to an INTEGER with the kind type parameter of the other argument as-if a call to INT — Convert to integer type occurred.

Specific names:
NameArgumentReturn typeStandard
IEOR(A)INTEGER AINTEGERFortran 90 and later
BIEOR(A)INTEGER(1) AINTEGER(1)GNU extension
IIEOR(A)INTEGER(2) AINTEGER(2)GNU extension
JIEOR(A)INTEGER(4) AINTEGER(4)GNU extension
KIEOR(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

IOR — Bitwise logical or, IAND — Bitwise logical and, IBITS — Bit extraction, IBSET — Set bit, IBCLR — Clear bit, NOT — Logical negation


9.146 IERRNO — Get the last system error number

Description:

Returns the last system error number, as given by the C errno variable.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = IERRNO()

Arguments:

None

Return value:

The return value is of type INTEGER and of the default integer kind.

See also:

PERROR — Print system error message


9.147 IMAGE_INDEX — Function that converts a cosubscript to an image index

Description:

Returns the image index belonging to a cosubscript.

Standard:

Fortran 2008 and later

Class:

Inquiry function.

Syntax:

RESULT = IMAGE_INDEX(COARRAY, SUB)

Arguments:
COARRAYCoarray of any type.
SUBdefault integer rank-1 array of a size equal to the corank of COARRAY.
Return value:

Scalar default integer with the value of the image index which corresponds to the cosubscripts. For invalid cosubscripts the result is zero.

Example:
INTEGER :: array[2,-1:4,8,*]
! Writes  28 (or 0 if there are fewer than 28 images)
WRITE (*,*) IMAGE_INDEX (array, [2,0,3,1])
See also:

THIS_IMAGE — Function that returns the cosubscript index of this image, NUM_IMAGES — Function that returns the number of images


9.148 INDEX — Position of a substring within a string

Description:

Returns the position of the start of the first occurrence of string SUBSTRING as a substring in STRING, counting from one. If SUBSTRING is not present in STRING, zero is returned. If the BACK argument is present and true, the return value is the start of the last occurrence rather than the first.

Standard:

Fortran 77 and later, with KIND argument Fortran 2003 and later

Class:

Elemental function

Syntax:

RESULT = INDEX(STRING, SUBSTRING [, BACK [, KIND]])

Arguments:
STRINGShall be a scalar CHARACTER, with INTENT(IN)
SUBSTRINGShall be a scalar CHARACTER, with INTENT(IN)
BACK(Optional) Shall be a scalar LOGICAL, with INTENT(IN)
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER and of kind KIND. If KIND is absent, the return value is of default integer kind.

Specific names:
NameArgumentReturn typeStandard
INDEX(STRING, SUBSTRING)CHARACTERINTEGER(4)Fortran 77 and later
See also:

SCAN — Scan a string for the presence of a set of characters, VERIFY — Scan a string for characters not a given set


9.149 INT — Convert to integer type

Description:

Convert to integer type

Standard:

Fortran 77 and later, with boz-literal-constant Fortran 2008 and later.

Class:

Elemental function

Syntax:

RESULT = INT(A [, KIND))

Arguments:
AShall be of type INTEGER, REAL, or COMPLEX or a boz-literal-constant.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

These functions return a INTEGER variable or array under the following rules:

(A)

If A is of type INTEGER, INT(A) = A

(B)

If A is of type REAL and |A| < 1, INT(A) equals 0. If |A| \geq 1, then INT(A) is the integer whose magnitude is the largest integer that does not exceed the magnitude of A and whose sign is the same as the sign of A.

(C)

If A is of type COMPLEX, rule B is applied to the real part of A.

Example:
program test_int
  integer :: i = 42
  complex :: z = (-3.7, 1.0)
  print *, int(i)
  print *, int(z), int(z,8)
end program
Specific names:
NameArgumentReturn typeStandard
INT(A)REAL(4) AINTEGERFortran 77 and later
IFIX(A)REAL(4) AINTEGERFortran 77 and later
IDINT(A)REAL(8) AINTEGERFortran 77 and later

9.150 INT2 — Convert to 16-bit integer type

Description:

Convert to a KIND=2 integer type. This is equivalent to the standard INT intrinsic with an optional argument of KIND=2, and is only included for backwards compatibility.

The SHORT intrinsic is equivalent to INT2.

Standard:

GNU extension

Class:

Elemental function

Syntax:

RESULT = INT2(A)

Arguments:
AShall be of type INTEGER, REAL, or COMPLEX.
Return value:

The return value is a INTEGER(2) variable.

See also:

INT — Convert to integer type, INT8 — Convert to 64-bit integer type, LONG — Convert to integer type


9.151 INT8 — Convert to 64-bit integer type

Description:

Convert to a KIND=8 integer type. This is equivalent to the standard INT intrinsic with an optional argument of KIND=8, and is only included for backwards compatibility.

Standard:

GNU extension

Class:

Elemental function

Syntax:

RESULT = INT8(A)

Arguments:
AShall be of type INTEGER, REAL, or COMPLEX.
Return value:

The return value is a INTEGER(8) variable.

See also:

INT — Convert to integer type, INT2 — Convert to 16-bit integer type, LONG — Convert to integer type


9.152 IOR — Bitwise logical or

Description:

IOR returns the bitwise Boolean inclusive-OR of I and J.

Standard:

Fortran 90 and later, with boz-literal-constant Fortran 2008 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = IOR(I, J)

Arguments:
IThe type shall be INTEGER or a boz-literal-constant.
JThe type shall be INTEGER with the same kind type parameter as I or a boz-literal-constant. I and J shall not both be boz-literal-constants.
Return value:

The return type is INTEGER with the kind type parameter of the arguments. A boz-literal-constant is converted to an INTEGER with the kind type parameter of the other argument as-if a call to INT — Convert to integer type occurred.

Specific names:
NameArgumentReturn typeStandard
IOR(A)INTEGER AINTEGERFortran 90 and later
BIOR(A)INTEGER(1) AINTEGER(1)GNU extension
IIOR(A)INTEGER(2) AINTEGER(2)GNU extension
JIOR(A)INTEGER(4) AINTEGER(4)GNU extension
KIOR(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

IEOR — Bitwise logical exclusive or, IAND — Bitwise logical and, IBITS — Bit extraction, IBSET — Set bit, IBCLR — Clear bit, NOT — Logical negation


9.153 IPARITY — Bitwise XOR of array elements

Description:

Reduces with bitwise XOR (exclusive or) the elements of ARRAY along dimension DIM if the corresponding element in MASK is TRUE.

Standard:

Fortran 2008 and later

Class:

Transformational function

Syntax:
RESULT = IPARITY(ARRAY[, MASK])
RESULT = IPARITY(ARRAY, DIM[, MASK])
Arguments:
ARRAYShall be an array of type INTEGER
DIM(Optional) shall be a scalar of type INTEGER with a value in the range from 1 to n, where n equals the rank of ARRAY.
MASK(Optional) shall be of type LOGICAL and either be a scalar or an array of the same shape as ARRAY.
Return value:

The result is of the same type as ARRAY.

If DIM is absent, a scalar with the bitwise XOR of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:
PROGRAM test_iparity
  INTEGER(1) :: a(2)

  a(1) = int(b'00100100', 1)
  a(2) = int(b'01101010', 1)

  ! prints 01001110
  PRINT '(b8.8)', IPARITY(a)
END PROGRAM
See also:

IANY — Bitwise OR of array elements, IALL — Bitwise AND of array elements, IEOR — Bitwise logical exclusive or, PARITY — Reduction with exclusive OR


9.154 IRAND — Integer pseudo-random number

Description:

IRAND(FLAG) returns a pseudo-random number from a uniform distribution between 0 and a system-dependent limit (which is in most cases 2147483647). If FLAG is 0, the next number in the current sequence is returned; if FLAG is 1, the generator is restarted by CALL SRAND(0); if FLAG has any other value, it is used as a new seed with SRAND.

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. It implements a simple modulo generator as provided by g77. For new code, one should consider the use of RANDOM_NUMBER — Pseudo-random number as it implements a superior algorithm.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = IRAND(I)

Arguments:
IShall be a scalar INTEGER of kind 4.
Return value:

The return value is of INTEGER(kind=4) type.

Example:
program test_irand
  integer,parameter :: seed = 86456
  
  call srand(seed)
  print *, irand(), irand(), irand(), irand()
  print *, irand(seed), irand(), irand(), irand()
end program test_irand

9.155 IS_CONTIGUOUS — Test whether an array is contiguous

Description:

IS_CONTIGUOUS tests whether an array is contiguous.

Standard:

Fortran 2008 and later

Class:

Inquiry function

Syntax:

RESULT = IS_CONTIGUOUS(ARRAY)

Arguments:
ARRAYShall be an array of any type.
Return value:

Returns a LOGICAL of the default kind, which .TRUE. if ARRAY is contiguous and false otherwise.

Example:
program test
  integer :: a(10)
  a = [1,2,3,4,5,6,7,8,9,10]
  call sub (a)      ! every element, is contiguous
  call sub (a(::2)) ! every other element, is noncontiguous
contains
  subroutine sub (x)
    integer :: x(:)
    if (is_contiguous (x)) then
      write (*,*) 'X is contiguous'
    else
      write (*,*) 'X is not contiguous'
    end if
  end subroutine sub
end program test

9.156 IS_IOSTAT_END — Test for end-of-file value

Description:

IS_IOSTAT_END tests whether an variable has the value of the I/O status “end of file”. The function is equivalent to comparing the variable with the IOSTAT_END parameter of the intrinsic module ISO_FORTRAN_ENV.

Standard:

Fortran 2003 and later

Class:

Elemental function

Syntax:

RESULT = IS_IOSTAT_END(I)

Arguments:
IShall be of the type INTEGER.
Return value:

Returns a LOGICAL of the default kind, which .TRUE. if I has the value which indicates an end of file condition for IOSTAT= specifiers, and is .FALSE. otherwise.

Example:
PROGRAM iostat
  IMPLICIT NONE
  INTEGER :: stat, i
  OPEN(88, FILE='test.dat')
  READ(88, *, IOSTAT=stat) i
  IF(IS_IOSTAT_END(stat)) STOP 'END OF FILE'
END PROGRAM

9.157 IS_IOSTAT_EOR — Test for end-of-record value

Description:

IS_IOSTAT_EOR tests whether an variable has the value of the I/O status “end of record”. The function is equivalent to comparing the variable with the IOSTAT_EOR parameter of the intrinsic module ISO_FORTRAN_ENV.

Standard:

Fortran 2003 and later

Class:

Elemental function

Syntax:

RESULT = IS_IOSTAT_EOR(I)

Arguments:
IShall be of the type INTEGER.
Return value:

Returns a LOGICAL of the default kind, which .TRUE. if I has the value which indicates an end of file condition for IOSTAT= specifiers, and is .FALSE. otherwise.

Example:
PROGRAM iostat
  IMPLICIT NONE
  INTEGER :: stat, i(50)
  OPEN(88, FILE='test.dat', FORM='UNFORMATTED')
  READ(88, IOSTAT=stat) i
  IF(IS_IOSTAT_EOR(stat)) STOP 'END OF RECORD'
END PROGRAM

9.158 ISATTY — Whether a unit is a terminal device.

Description:

Determine whether a unit is connected to a terminal device.

Standard:

GNU extension

Class:

Function

Syntax:

RESULT = ISATTY(UNIT)

Arguments:
UNITShall be a scalar INTEGER.
Return value:

Returns .TRUE. if the UNIT is connected to a terminal device, .FALSE. otherwise.

Example:
PROGRAM test_isatty
  INTEGER(kind=1) :: unit
  DO unit = 1, 10
    write(*,*) isatty(unit=unit)
  END DO
END PROGRAM
See also:

TTYNAM — Get the name of a terminal device.


9.159 ISHFT — Shift bits

Description:

ISHFT returns a value corresponding to I with all of the bits shifted SHIFT places. A value of SHIFT greater than zero corresponds to a left shift, a value of zero corresponds to no shift, and a value less than zero corresponds to a right shift. If the absolute value of SHIFT is greater than BIT_SIZE(I), the value is undefined. Bits shifted out from the left end or right end are lost; zeros are shifted in from the opposite end.

Standard:

Fortran 90 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = ISHFT(I, SHIFT)

Arguments:
IThe type shall be INTEGER.
SHIFTThe type shall be INTEGER.
Return value:

The return value is of type INTEGER and of the same kind as I.

Specific names:
NameArgumentReturn typeStandard
ISHFT(A)INTEGER AINTEGERFortran 90 and later
BSHFT(A)INTEGER(1) AINTEGER(1)GNU extension
IISHFT(A)INTEGER(2) AINTEGER(2)GNU extension
JISHFT(A)INTEGER(4) AINTEGER(4)GNU extension
KISHFT(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

ISHFTC — Shift bits circularly


9.160 ISHFTC — Shift bits circularly

Description:

ISHFTC returns a value corresponding to I with the rightmost SIZE bits shifted circularly SHIFT places; that is, bits shifted out one end are shifted into the opposite end. A value of SHIFT greater than zero corresponds to a left shift, a value of zero corresponds to no shift, and a value less than zero corresponds to a right shift. The absolute value of SHIFT must be less than SIZE. If the SIZE argument is omitted, it is taken to be equivalent to BIT_SIZE(I).

Standard:

Fortran 90 and later, has overloads that are GNU extensions

Class:

Elemental function

Syntax:

RESULT = ISHFTC(I, SHIFT [, SIZE])

Arguments:
IThe type shall be INTEGER.
SHIFTThe type shall be INTEGER.
SIZE(Optional) The type shall be INTEGER; the value must be greater than zero and less than or equal to BIT_SIZE(I).
Return value:

The return value is of type INTEGER and of the same kind as I.

Specific names:
NameArgumentReturn typeStandard
ISHFTC(A)INTEGER AINTEGERFortran 90 and later
BSHFTC(A)INTEGER(1) AINTEGER(1)GNU extension
IISHFTC(A)INTEGER(2) AINTEGER(2)GNU extension
JISHFTC(A)INTEGER(4) AINTEGER(4)GNU extension
KISHFTC(A)INTEGER(8) AINTEGER(8)GNU extension
See also:

ISHFT — Shift bits


9.161 ISNAN — Test for a NaN

Description:

ISNAN tests whether a floating-point value is an IEEE Not-a-Number (NaN).

Standard:

GNU extension

Class:

Elemental function

Syntax:

ISNAN(X)

Arguments:
XVariable of the type REAL.
Return value:

Returns a default-kind LOGICAL. The returned value is TRUE if X is a NaN and FALSE otherwise.

Example:
program test_nan
  implicit none
  real :: x
  x = -1.0
  x = sqrt(x)
  if (isnan(x)) stop '"x" is a NaN'
end program test_nan

9.162 ITIME — Get current local time subroutine (hour/minutes/seconds)

Description:

ITIME(VALUES) Fills VALUES with the numerical values at the current local time. The hour (in the range 1-24), minute (in the range 1-60), and seconds (in the range 1-60) appear in elements 1, 2, and 3 of VALUES, respectively.

This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the DATE_AND_TIME — Date and time subroutine intrinsic defined by the Fortran 95 standard.

Standard:

GNU extension

Class:

Subroutine

Syntax:

CALL ITIME(VALUES)

Arguments:
VALUESThe type shall be INTEGER, DIMENSION(3) and the kind shall be the default integer kind.
Return value:

Does not return anything.

Example:
program test_itime
  integer, dimension(3) :: tarray
  call itime(tarray)
  print *, tarray(1)
  print *, tarray(2)
  print *, tarray(3)
end program test_itime
See also:

DATE_AND_TIME — Date and time subroutine


9.163 KILL — Send a signal to a process

Description:

Sends the signal specified by SIG to the process PID. See kill(2).

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:

GNU extension

Standard:

GNU extension

Class:

Subroutine, function

Syntax:
CALL KILL(PID, SIG [, STATUS])
STATUS = KILL(PID, SIG)
Arguments:
PIDShall be a scalar INTEGER with INTENT(IN).
SIGShall be a scalar INTEGER with INTENT(IN).
STATUS[Subroutine](Optional) Shall be a scalar INTEGER. Returns 0 on success; otherwise a system-specific error code is returned.
STATUS[Function] The kind type parameter is that of pid. Returns 0 on success; otherwise a system-specific error code is returned.
See also:

ABORT — Abort the program, EXIT — Exit the program with status.


9.164 KIND — Kind of an entity

Description:

KIND(X) returns the kind value of the entity X.

Standard:

Fortran 95 and later

Class:

Inquiry function

Syntax:

K = KIND(X)

Arguments:
XShall be of type LOGICAL, INTEGER, REAL, COMPLEX or CHARACTER. It may be scalar or array valued.
Return value:

The return value is a scalar of type INTEGER and of the default integer kind.

Example:
program test_kind
  integer,parameter :: kc = kind(' ')
  integer,parameter :: kl = kind(.true.)

  print *, "The default character kind is ", kc
  print *, "The default logical kind is ", kl
end program test_kind

9.165 LBOUND — Lower dimension bounds of an array

Description:

Returns the lower bounds of an array, or a single lower bound along the DIM dimension.

Standard:

Fortran 90 and later, with KIND argument Fortran 2003 and later

Class:

Inquiry function

Syntax:

RESULT = LBOUND(ARRAY [, DIM [, KIND]])

Arguments:
ARRAYShall be an array, of any type.
DIM(Optional) Shall be a scalar INTEGER.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is absent, the result is an array of the lower bounds of ARRAY. If DIM is present, the result is a scalar corresponding to the lower bound of the array along that dimension. If ARRAY is an expression rather than a whole array or array structure component, or if it has a zero extent along the relevant dimension, the lower bound is taken to be 1.

See also:

UBOUND — Upper dimension bounds of an array, LCOBOUND — Lower codimension bounds of an array


9.166 LCOBOUND — Lower codimension bounds of an array

Description:

Returns the lower bounds of a coarray, or a single lower cobound along the DIM codimension.

Standard:

Fortran 2008 and later

Class:

Inquiry function

Syntax:

RESULT = LCOBOUND(COARRAY [, DIM [, KIND]])

Arguments:
ARRAYShall be an coarray, of any type.
DIM(Optional) Shall be a scalar INTEGER.
KIND(Optional) An INTEGER initialization expression indicating the kind parameter of the result.
Return value:

The return value is of type INTEGER and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is absent, the result is an array of the lower cobounds of COARRAY. If DIM is present, the result is a scalar corresponding to the lower cobound of the array along that codimension.

See also:

UCOBOUND — Upper codimension bounds of an array, LBOUND — Lower dimension bounds of an array


9.167 LEADZ — Number of leading zero bits of an integer

Description:

LEADZ returns the number of leading zero bits of an integer.

Standard:

Fortran 2008 and later

Class:

Elemental function

Syntax:

RESULT = LEADZ(I)

Arguments:
IShall be of type INTEGER.
Return value:

The type of the return value is the default INTEGER. If all the bits of I are zero, the result value is BIT_SIZE(I).

Example:
PROGRAM test_leadz
  WRITE (*,*) BIT_SIZE(1)  ! prints 32
  WRITE (*,*) LEADZ(1)     ! prints 31
END PROGRAM
See also:

BIT_SIZE — Bit size inquiry function, TRAILZ — Number of trailing zero bits of an integer, POPCNT — Number of bits set, POPPAR — Parity of the number of bits set


9.168 LEN — Length of a character entity

Description:

Returns the length of a character string. If STRING is an array, the length of an element of STRING is returned. Note that STRING need no