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@settitle The GNU Fortran Compiler

@settitle The GNU Fortran Compiler

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Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc.

Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document

Permission is granted to copy, distribute and/or modify this document

under the terms of the GNU Free Documentation License, Version 1.2 or

under the terms of the GNU Free Documentation License, Version 1.2 or

any later version published by the Free Software Foundation; with the

any later version published by the Free Software Foundation; with the

Invariant Sections being ``Funding Free Software'', the Front-Cover

Invariant Sections being ``Funding Free Software'', the Front-Cover

Texts being (a) (see below), and with the Back-Cover Texts being (b)

Texts being (a) (see below), and with the Back-Cover Texts being (b)

(see below).  A copy of the license is included in the section entitled

(see below).  A copy of the license is included in the section entitled

``GNU Free Documentation License''.

``GNU Free Documentation License''.

(a) The FSF's Front-Cover Text is:

(a) The FSF's Front-Cover Text is:

     A GNU Manual

     A GNU Manual

(b) The FSF's Back-Cover Text is:

(b) The FSF's Back-Cover Text is:

     You have freedom to copy and modify this GNU Manual, like GNU

     You have freedom to copy and modify this GNU Manual, like GNU

     software.  Copies published by the Free Software Foundation raise

     software.  Copies published by the Free Software Foundation raise

     funds for GNU development.

     funds for GNU development.

@end copying

@end copying

@ifinfo

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@dircategory Software development

@dircategory Software development

@direntry

@direntry

* gfortran: (gfortran).                  The GNU Fortran Compiler.

* gfortran: (gfortran).                  The GNU Fortran Compiler.

@end direntry

@end direntry

This file documents the use and the internals of

This file documents the use and the internals of

the GNU Fortran compiler, (@command{gfortran}).

the GNU Fortran compiler, (@command{gfortran}).

Published by the Free Software Foundation

Published by the Free Software Foundation

51 Franklin Street, Fifth Floor

51 Franklin Street, Fifth Floor

Boston, MA 02110-1301 USA

Boston, MA 02110-1301 USA

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@title Using GNU Fortran

@title Using GNU Fortran

@versionsubtitle

@versionsubtitle

@author The @t{gfortran} team

@author The @t{gfortran} team

@page

@page

@vskip 0pt plus 1filll

@vskip 0pt plus 1filll

Published by the Free Software Foundation@*

Published by the Free Software Foundation@*

51 Franklin Street, Fifth Floor@*

51 Franklin Street, Fifth Floor@*

Boston, MA 02110-1301, USA@*

Boston, MA 02110-1301, USA@*

@c Last printed ??ber, 19??.@*

@c Last printed ??ber, 19??.@*

@c Printed copies are available for $? each.@*

@c Printed copies are available for $? each.@*

@c ISBN ???

@c ISBN ???

@sp 1

@sp 1

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@contents

@contents

@page

@page

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c TexInfo table of contents.

@c TexInfo table of contents.

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@ifnottex

@ifnottex

@node Top

@node Top

@top Introduction

@top Introduction

@cindex Introduction

@cindex Introduction

This manual documents the use of @command{gfortran},

This manual documents the use of @command{gfortran},

the GNU Fortran compiler. You can find in this manual how to invoke

the GNU Fortran compiler. You can find in this manual how to invoke

@command{gfortran}, as well as its features and incompatibilities.

@command{gfortran}, as well as its features and incompatibilities.

@ifset DEVELOPMENT

@ifset DEVELOPMENT

@emph{Warning:} This document, and the compiler it describes, are still

@emph{Warning:} This document, and the compiler it describes, are still

under development.  While efforts are made to keep it up-to-date, it might

under development.  While efforts are made to keep it up-to-date, it might

not accurately reflect the status of the most recent GNU Fortran compiler.

not accurately reflect the status of the most recent GNU Fortran compiler.

@end ifset

@end ifset

@comment

@comment

@comment  When you add a new menu item, please keep the right hand

@comment  When you add a new menu item, please keep the right hand

@comment  aligned to the same column.  Do not use tabs.  This provides

@comment  aligned to the same column.  Do not use tabs.  This provides

@comment  better formatting.

@comment  better formatting.

@comment

@comment

@menu

@menu

* Introduction::

* Introduction::

Part I: Invoking GNU Fortran

Part I: Invoking GNU Fortran

* Invoking GNU Fortran:: Command options supported by @command{gfortran}.

* Invoking GNU Fortran:: Command options supported by @command{gfortran}.

* Runtime::              Influencing runtime behavior with environment variables.

* Runtime::              Influencing runtime behavior with environment variables.

Part II: Language Reference

Part II: Language Reference

* Fortran 2003 and 2008 status::  Fortran 2003 and 2008 features supported by GNU Fortran.

* Fortran 2003 and 2008 status::  Fortran 2003 and 2008 features supported by GNU Fortran.

* Compiler Characteristics::      User-visible implementation details.

* Compiler Characteristics::      User-visible implementation details.

* Mixed-Language Programming::    Interoperability with C

* Mixed-Language Programming::    Interoperability with C

* Extensions::           Language extensions implemented by GNU Fortran.

* Extensions::           Language extensions implemented by GNU Fortran.

* Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.

* Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.

* Intrinsic Modules::    Intrinsic modules supported by GNU Fortran.

* Intrinsic Modules::    Intrinsic modules supported by GNU Fortran.

* Contributing::         How you can help.

* Contributing::         How you can help.

* Copying::              GNU General Public License says

* Copying::              GNU General Public License says

                         how you can copy and share GNU Fortran.

                         how you can copy and share GNU Fortran.

* GNU Free Documentation License::

* GNU Free Documentation License::

                         How you can copy and share this manual.

                         How you can copy and share this manual.

* Funding::              How to help assure continued work for free software.

* Funding::              How to help assure continued work for free software.

* Option Index::         Index of command line options

* Option Index::         Index of command line options

* Keyword Index::        Index of concepts

* Keyword Index::        Index of concepts

@end menu

@end menu

@end ifnottex

@end ifnottex

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c Introduction

@c Introduction

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node Introduction

@node Introduction

@chapter Introduction

@chapter Introduction

@c The following duplicates the text on the TexInfo table of contents.

@c The following duplicates the text on the TexInfo table of contents.

@iftex

@iftex

This manual documents the use of @command{gfortran}, the GNU Fortran

This manual documents the use of @command{gfortran}, the GNU Fortran

compiler. You can find in this manual how to invoke @command{gfortran},

compiler. You can find in this manual how to invoke @command{gfortran},

as well as its features and incompatibilities.

as well as its features and incompatibilities.

@ifset DEVELOPMENT

@ifset DEVELOPMENT

@emph{Warning:} This document, and the compiler it describes, are still

@emph{Warning:} This document, and the compiler it describes, are still

under development.  While efforts are made to keep it up-to-date, it

under development.  While efforts are made to keep it up-to-date, it

might not accurately reflect the status of the most recent GNU Fortran

might not accurately reflect the status of the most recent GNU Fortran

compiler.

compiler.

@end ifset

@end ifset

@end iftex

@end iftex

The GNU Fortran compiler front end was

The GNU Fortran compiler front end was

designed initially as a free replacement for,

designed initially as a free replacement for,

or alternative to, the unix @command{f95} command;

or alternative to, the unix @command{f95} command;

@command{gfortran} is the command you'll use to invoke the compiler.

@command{gfortran} is the command you'll use to invoke the compiler.

@menu

@menu

* About GNU Fortran::    What you should know about the GNU Fortran compiler.

* About GNU Fortran::    What you should know about the GNU Fortran compiler.

* GNU Fortran and GCC::  You can compile Fortran, C, or other programs.

* GNU Fortran and GCC::  You can compile Fortran, C, or other programs.

* Preprocessing and conditional compilation:: The Fortran preprocessor

* Preprocessing and conditional compilation:: The Fortran preprocessor

* GNU Fortran and G77::  Why we chose to start from scratch.

* GNU Fortran and G77::  Why we chose to start from scratch.

* Project Status::       Status of GNU Fortran, roadmap, proposed extensions.

* Project Status::       Status of GNU Fortran, roadmap, proposed extensions.

* Standards::            Standards supported by GNU Fortran.

* Standards::            Standards supported by GNU Fortran.

@end menu

@end menu

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c About GNU Fortran

@c About GNU Fortran

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node About GNU Fortran

@node About GNU Fortran

@section About GNU Fortran

@section About GNU Fortran

The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards

The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards

completely, parts of the Fortran 2003 and Fortran 2008 standards, and

completely, parts of the Fortran 2003 and Fortran 2008 standards, and

several vendor extensions. The development goal is to provide the

several vendor extensions. The development goal is to provide the

following features:

following features:

@itemize @bullet

@itemize @bullet

@item

@item

Read a user's program,

Read a user's program,

stored in a file and containing instructions written

stored in a file and containing instructions written

in Fortran 77, Fortran 90, Fortran 95, Fortran 2003 or Fortran 2008.

in Fortran 77, Fortran 90, Fortran 95, Fortran 2003 or Fortran 2008.

This file contains @dfn{source code}.

This file contains @dfn{source code}.

@item

@item

Translate the user's program into instructions a computer

Translate the user's program into instructions a computer

can carry out more quickly than it takes to translate the

can carry out more quickly than it takes to translate the

instructions in the first

instructions in the first

place.  The result after compilation of a program is

place.  The result after compilation of a program is

@dfn{machine code},

@dfn{machine code},

code designed to be efficiently translated and processed

code designed to be efficiently translated and processed

by a machine such as your computer.

by a machine such as your computer.

Humans usually aren't as good writing machine code

Humans usually aren't as good writing machine code

as they are at writing Fortran (or C++, Ada, or Java),

as they are at writing Fortran (or C++, Ada, or Java),

because it is easy to make tiny mistakes writing machine code.

because it is easy to make tiny mistakes writing machine code.

@item

@item

Provide the user with information about the reasons why

Provide the user with information about the reasons why

the compiler is unable to create a binary from the source code.

the compiler is unable to create a binary from the source code.

Usually this will be the case if the source code is flawed.

Usually this will be the case if the source code is flawed.

The Fortran 90 standard requires that the compiler can point out

The Fortran 90 standard requires that the compiler can point out

mistakes to the user.

mistakes to the user.

An incorrect usage of the language causes an @dfn{error message}.

An incorrect usage of the language causes an @dfn{error message}.

The compiler will also attempt to diagnose cases where the

The compiler will also attempt to diagnose cases where the

user's program contains a correct usage of the language,

user's program contains a correct usage of the language,

but instructs the computer to do something questionable.

but instructs the computer to do something questionable.

This kind of diagnostics message is called a @dfn{warning message}.

This kind of diagnostics message is called a @dfn{warning message}.

@item

@item

Provide optional information about the translation passes

Provide optional information about the translation passes

from the source code to machine code.

from the source code to machine code.

This can help a user of the compiler to find the cause of

This can help a user of the compiler to find the cause of

certain bugs which may not be obvious in the source code,

certain bugs which may not be obvious in the source code,

but may be more easily found at a lower level compiler output.

but may be more easily found at a lower level compiler output.

It also helps developers to find bugs in the compiler itself.

It also helps developers to find bugs in the compiler itself.

@item

@item

Provide information in the generated machine code that can

Provide information in the generated machine code that can

make it easier to find bugs in the program (using a debugging tool,

make it easier to find bugs in the program (using a debugging tool,

called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).

called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).

@item

@item

Locate and gather machine code already generated to

Locate and gather machine code already generated to

perform actions requested by statements in the user's program.

perform actions requested by statements in the user's program.

This machine code is organized into @dfn{modules} and is located

This machine code is organized into @dfn{modules} and is located

and @dfn{linked} to the user program.

and @dfn{linked} to the user program.

@end itemize

@end itemize

The GNU Fortran compiler consists of several components:

The GNU Fortran compiler consists of several components:

@itemize @bullet

@itemize @bullet

@item

@item

A version of the @command{gcc} command

A version of the @command{gcc} command

(which also might be installed as the system's @command{cc} command)

(which also might be installed as the system's @command{cc} command)

that also understands and accepts Fortran source code.

that also understands and accepts Fortran source code.

The @command{gcc} command is the @dfn{driver} program for

The @command{gcc} command is the @dfn{driver} program for

all the languages in the GNU Compiler Collection (GCC);

all the languages in the GNU Compiler Collection (GCC);

With @command{gcc},

With @command{gcc},

you can compile the source code of any language for

you can compile the source code of any language for

which a front end is available in GCC.

which a front end is available in GCC.

@item

@item

The @command{gfortran} command itself,

The @command{gfortran} command itself,

which also might be installed as the

which also might be installed as the

system's @command{f95} command.

system's @command{f95} command.

@command{gfortran} is just another driver program,

@command{gfortran} is just another driver program,

but specifically for the Fortran compiler only.

but specifically for the Fortran compiler only.

The difference with @command{gcc} is that @command{gfortran}

The difference with @command{gcc} is that @command{gfortran}

will automatically link the correct libraries to your program.

will automatically link the correct libraries to your program.

@item

@item

A collection of run-time libraries.

A collection of run-time libraries.

These libraries contain the machine code needed to support

These libraries contain the machine code needed to support

capabilities of the Fortran language that are not directly

capabilities of the Fortran language that are not directly

provided by the machine code generated by the

provided by the machine code generated by the

@command{gfortran} compilation phase,

@command{gfortran} compilation phase,

such as intrinsic functions and subroutines,

such as intrinsic functions and subroutines,

and routines for interaction with files and the operating system.

and routines for interaction with files and the operating system.

@c and mechanisms to spawn,

@c and mechanisms to spawn,

@c unleash and pause threads in parallelized code.

@c unleash and pause threads in parallelized code.

@item

@item

The Fortran compiler itself, (@command{f951}).

The Fortran compiler itself, (@command{f951}).

This is the GNU Fortran parser and code generator,

This is the GNU Fortran parser and code generator,

linked to and interfaced with the GCC backend library.

linked to and interfaced with the GCC backend library.

@command{f951} ``translates'' the source code to

@command{f951} ``translates'' the source code to

assembler code.  You would typically not use this

assembler code.  You would typically not use this

program directly;

program directly;

instead, the @command{gcc} or @command{gfortran} driver

instead, the @command{gcc} or @command{gfortran} driver

programs will call it for you.

programs will call it for you.

@end itemize

@end itemize

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c GNU Fortran and GCC

@c GNU Fortran and GCC

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node GNU Fortran and GCC

@node GNU Fortran and GCC

@section GNU Fortran and GCC

@section GNU Fortran and GCC

@cindex GNU Compiler Collection

@cindex GNU Compiler Collection

@cindex GCC

@cindex GCC

GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}.  GCC

GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}.  GCC

consists of a collection of front ends for various languages, which

consists of a collection of front ends for various languages, which

translate the source code into a language-independent form called

translate the source code into a language-independent form called

@dfn{GENERIC}.  This is then processed by a common middle end which

@dfn{GENERIC}.  This is then processed by a common middle end which

provides optimization, and then passed to one of a collection of back

provides optimization, and then passed to one of a collection of back

ends which generate code for different computer architectures and

ends which generate code for different computer architectures and

operating systems.

operating systems.

Functionally, this is implemented with a driver program (@command{gcc})

Functionally, this is implemented with a driver program (@command{gcc})

which provides the command-line interface for the compiler.  It calls

which provides the command-line interface for the compiler.  It calls

the relevant compiler front-end program (e.g., @command{f951} for

the relevant compiler front-end program (e.g., @command{f951} for

Fortran) for each file in the source code, and then calls the assembler

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

and linker as appropriate to produce the compiled output. In a copy of

GCC which has been compiled with Fortran language support enabled,

GCC which has been compiled with Fortran language support enabled,

@command{gcc} will recognize files with @file{.f}, @file{.for}, @file{.ftn},

@command{gcc} will recognize files with @file{.f}, @file{.for}, @file{.ftn},

@file{.f90}, @file{.f95}, @file{.f03} and @file{.f08} extensions as

@file{.f90}, @file{.f95}, @file{.f03} and @file{.f08} extensions as

Fortran source code, and compile it accordingly. A @command{gfortran}

Fortran source code, and compile it accordingly. A @command{gfortran}

driver program is also provided, which is identical to @command{gcc}

driver program is also provided, which is identical to @command{gcc}

except that it automatically links the Fortran runtime libraries into the

except that it automatically links the Fortran runtime libraries into the

compiled program.

compiled program.

Source files with @file{.f}, @file{.for}, @file{.fpp}, @file{.ftn}, @file{.F},

Source files with @file{.f}, @file{.for}, @file{.fpp}, @file{.ftn}, @file{.F},

@file{.FOR}, @file{.FPP}, and @file{.FTN} extensions are treated as fixed form.

@file{.FOR}, @file{.FPP}, and @file{.FTN} extensions are treated as fixed form.

Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.f08},

Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.f08},

@file{.F90}, @file{.F95}, @file{.F03} and @file{.F08} extensions are

@file{.F90}, @file{.F95}, @file{.F03} and @file{.F08} extensions are

treated as free form.  The capitalized versions of either form are run

treated as free form.  The capitalized versions of either form are run

through preprocessing. Source files with the lower case @file{.fpp}

through preprocessing. Source files with the lower case @file{.fpp}

extension are also run through preprocessing.

extension are also run through preprocessing.

This manual specifically documents the Fortran front end, which handles

This manual specifically documents the Fortran front end, which handles

the programming language's syntax and semantics.  The aspects of GCC

the programming language's syntax and semantics.  The aspects of GCC

which relate to the optimization passes and the back-end code generation

which relate to the optimization passes and the back-end code generation

are documented in the GCC manual; see

are documented in the GCC manual; see

@ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}.

@ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}.

The two manuals together provide a complete reference for the GNU

The two manuals together provide a complete reference for the GNU

Fortran compiler.

Fortran compiler.

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c Preprocessing and conditional compilation

@c Preprocessing and conditional compilation

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node Preprocessing and conditional compilation

@node Preprocessing and conditional compilation

@section Preprocessing and conditional compilation

@section Preprocessing and conditional compilation

@cindex CPP

@cindex CPP

@cindex FPP

@cindex FPP

@cindex Conditional compilation

@cindex Conditional compilation

@cindex Preprocessing

@cindex Preprocessing

@cindex preprocessor, include file handling

@cindex preprocessor, include file handling

Many Fortran compilers including GNU Fortran allow passing the source code

Many Fortran compilers including GNU Fortran allow passing the source code

through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,

through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,

FPP) to allow for conditional compilation. In the case of GNU Fortran,

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

this is the GNU C Preprocessor in the traditional mode. On systems with

case-preserving file names, the preprocessor is automatically invoked if the

case-preserving file names, the preprocessor is automatically invoked if the

filename extension is @code{.F}, @code{.FOR}, @code{.FTN}, @code{.fpp},

filename extension is @code{.F}, @code{.FOR}, @code{.FTN}, @code{.fpp},

@code{.FPP}, @code{.F90}, @code{.F95}, @code{.F03} or @code{.F08}. To manually

@code{.FPP}, @code{.F90}, @code{.F95}, @code{.F03} or @code{.F08}. To manually

invoke the preprocessor on any file, use @option{-cpp}, to disable

invoke the preprocessor on any file, use @option{-cpp}, to disable

preprocessing on files where the preprocessor is run automatically, use

preprocessing on files where the preprocessor is run automatically, use

@option{-nocpp}.

@option{-nocpp}.

If a preprocessed file includes another file with the Fortran @code{INCLUDE}

If a preprocessed file includes another file with the Fortran @code{INCLUDE}

statement, the included file is not preprocessed. To preprocess included

statement, the included file is not preprocessed. To preprocess included

files, use the equivalent preprocessor statement @code{#include}.

files, use the equivalent preprocessor statement @code{#include}.

If GNU Fortran invokes the preprocessor, @code{__GFORTRAN__}

If GNU Fortran invokes the preprocessor, @code{__GFORTRAN__}

is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and

is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and

@code{__GNUC_PATCHLEVEL__} can be used to determine the version of the

@code{__GNUC_PATCHLEVEL__} can be used to determine the version of the

compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.

compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.

While CPP is the de-facto standard for preprocessing Fortran code,

While CPP is the de-facto standard for preprocessing Fortran code,

Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines

Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines

Conditional Compilation, which is not widely used and not directly

Conditional Compilation, which is not widely used and not directly

supported by the GNU Fortran compiler. You can use the program coco

supported by the GNU Fortran compiler. You can use the program coco

to preprocess such files (@uref{http://users.erols.com/dnagle/coco.html}).

to preprocess such files (@uref{http://users.erols.com/dnagle/coco.html}).

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c GNU Fortran and G77

@c GNU Fortran and G77

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node GNU Fortran and G77

@node GNU Fortran and G77

@section GNU Fortran and G77

@section GNU Fortran and G77

@cindex Fortran 77

@cindex Fortran 77

@cindex @command{g77}

@cindex @command{g77}

The GNU Fortran compiler is the successor to @command{g77}, the Fortran

The GNU Fortran compiler is the successor to @command{g77}, the Fortran

77 front end included in GCC prior to version 4.  It is an entirely new

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

program that has been designed to provide Fortran 95 support and

extensibility for future Fortran language standards, as well as providing

extensibility for future Fortran language standards, as well as providing

backwards compatibility for Fortran 77 and nearly all of the GNU language

backwards compatibility for Fortran 77 and nearly all of the GNU language

extensions supported by @command{g77}.

extensions supported by @command{g77}.

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c Project Status

@c Project Status

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node Project Status

@node Project Status

@section Project Status

@section Project Status

@quotation

@quotation

As soon as @command{gfortran} can parse all of the statements correctly,

As soon as @command{gfortran} can parse all of the statements correctly,

it will be in the ``larva'' state.

it will be in the ``larva'' state.

When we generate code, the ``puppa'' state.

When we generate code, the ``puppa'' state.

When @command{gfortran} is done,

When @command{gfortran} is done,

we'll see if it will be a beautiful butterfly,

we'll see if it will be a beautiful butterfly,

or just a big bug....

or just a big bug....

--Andy Vaught, April 2000

--Andy Vaught, April 2000

@end quotation

@end quotation

The start of the GNU Fortran 95 project was announced on

The start of the GNU Fortran 95 project was announced on

the GCC homepage in March 18, 2000

the GCC homepage in March 18, 2000

(even though Andy had already been working on it for a while,

(even though Andy had already been working on it for a while,

of course).

of course).

The GNU Fortran compiler is able to compile nearly all

The GNU Fortran compiler is able to compile nearly all

standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,

standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,

including a number of standard and non-standard extensions, and can be

including a number of standard and non-standard extensions, and can be

used on real-world programs.  In particular, the supported extensions

used on real-world programs.  In particular, the supported extensions

include OpenMP, Cray-style pointers, and several Fortran 2003 and Fortran

include OpenMP, Cray-style pointers, and several Fortran 2003 and Fortran

2008 features such as enumeration, stream I/O, and some of the

2008 features such as enumeration, stream I/O, and some of the

enhancements to allocatable array support from TR 15581.  However, it is

enhancements to allocatable array support from TR 15581.  However, it is

still under development and has a few remaining rough edges.

still under development and has a few remaining rough edges.

At present, the GNU Fortran compiler passes the

At present, the GNU Fortran compiler passes the

@uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,

@uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,

NIST Fortran 77 Test Suite}, and produces acceptable results on the

NIST Fortran 77 Test Suite}, and produces acceptable results on the

@uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.

@uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.

It also provides respectable performance on

It also provides respectable performance on

the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran

the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran

compiler benchmarks} and the

compiler benchmarks} and the

@uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html,

@uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html,

Livermore Fortran Kernels test}.  It has been used to compile a number of

Livermore Fortran Kernels test}.  It has been used to compile a number of

large real-world programs, including

large real-world programs, including

@uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM

@uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM

weather-forecasting code} and

weather-forecasting code} and

@uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum

@uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum

chemistry package}; see @url{http://gcc.gnu.org/wiki/GfortranApps} for an

chemistry package}; see @url{http://gcc.gnu.org/wiki/GfortranApps} for an

extended list.

extended list.

Among other things, the GNU Fortran compiler is intended as a replacement

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

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

G77 can be compiled with GNU Fortran, although there are a few minor known

regressions.

regressions.

The primary work remaining to be done on GNU Fortran falls into three

The primary work remaining to be done on GNU Fortran falls into three

categories: bug fixing (primarily regarding the treatment of invalid code

categories: bug fixing (primarily regarding the treatment of invalid code

and providing useful error messages), improving the compiler optimizations

and providing useful error messages), improving the compiler optimizations

and the performance of compiled code, and extending the compiler to support

and the performance of compiled code, and extending the compiler to support

future standards---in particular, Fortran 2003 and Fortran 2008.

future standards---in particular, Fortran 2003 and Fortran 2008.

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c Standards

@c Standards

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node Standards

@node Standards

@section Standards

@section Standards

@cindex Standards

@cindex Standards

@menu

@menu

* Varying Length Character Strings::

* Varying Length Character Strings::

@end menu

@end menu

The GNU Fortran compiler implements

The GNU Fortran compiler implements

ISO/IEC 1539:1997 (Fortran 95).  As such, it can also compile essentially all

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

standard-compliant Fortran 90 and Fortran 77 programs.   It also supports

the ISO/IEC TR-15581 enhancements to allocatable arrays, and

the ISO/IEC TR-15581 enhancements to allocatable arrays, and

the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,

the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,

OpenMP Application Program Interface v2.5} specification.

OpenMP Application Program Interface v2.5} specification.

In the future, the GNU Fortran compiler will also support ISO/IEC

In the future, the GNU Fortran compiler will also support ISO/IEC

1539-1:2004 (Fortran 2003) and future Fortran standards. Partial support

1539-1:2004 (Fortran 2003) and future Fortran standards. Partial support

of that standard is already provided; the current status of Fortran 2003

of that standard is already provided; the current status of Fortran 2003

support is reported in the @ref{Fortran 2003 status} section of the

support is reported in the @ref{Fortran 2003 status} section of the

documentation.

documentation.

The next version of the Fortran standard (Fortran 2008) is currently

The next version of the Fortran standard (Fortran 2008) is currently

being developed and the GNU Fortran compiler supports some of its new

being developed and the GNU Fortran compiler supports some of its new

features. This support is based on the latest draft of the standard

features. This support is based on the latest draft of the standard

(available from @url{http://www.nag.co.uk/sc22wg5/}) and no guarantee of

(available from @url{http://www.nag.co.uk/sc22wg5/}) and no guarantee of

future compatibility is made, as the final standard might differ from the

future compatibility is made, as the final standard might differ from the

draft. For more information, see the @ref{Fortran 2008 status} section.

draft. For more information, see the @ref{Fortran 2008 status} section.

Additionally, the GNU Fortran compilers supports the OpenMP specification

Additionally, the GNU Fortran compilers supports the OpenMP specification

(version 3.0, @url{http://openmp.org/wp/openmp-specifications/}).

(version 3.0, @url{http://openmp.org/wp/openmp-specifications/}).

@node Varying Length Character Strings

@node Varying Length Character Strings

@subsection Varying Length Character Strings

@subsection Varying Length Character Strings

@cindex Varying length character strings

@cindex Varying length character strings

@cindex Varying length strings

@cindex Varying length strings

@cindex strings, varying length

@cindex strings, varying length

The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000)

The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000)

varying length character strings. While GNU Fortran currently does not

varying length character strings. While GNU Fortran currently does not

support such strings directly, there exist two Fortran implementations

support such strings directly, there exist two Fortran implementations

for them, which work with GNU Fortran. They can be found at

for them, which work with GNU Fortran. They can be found at

@uref{http://www.fortran.com/@/iso_varying_string.f95} and at

@uref{http://www.fortran.com/@/iso_varying_string.f95} and at

@uref{ftp://ftp.nag.co.uk/@/sc22wg5/@/ISO_VARYING_STRING/}.

@uref{ftp://ftp.nag.co.uk/@/sc22wg5/@/ISO_VARYING_STRING/}.

@c =====================================================================

@c =====================================================================

@c PART I: INVOCATION REFERENCE

@c PART I: INVOCATION REFERENCE

@c =====================================================================

@c =====================================================================

@tex

@tex

\part{I}{Invoking GNU Fortran}

\part{I}{Invoking GNU Fortran}

@end tex

@end tex

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c Compiler Options

@c Compiler Options

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@include invoke.texi

@include invoke.texi

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c Runtime

@c Runtime

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node Runtime

@node Runtime

@chapter Runtime:  Influencing runtime behavior with environment variables

@chapter Runtime:  Influencing runtime behavior with environment variables

@cindex environment variable

@cindex environment variable

The behavior of the @command{gfortran} can be influenced by

The behavior of the @command{gfortran} can be influenced by

environment variables.

environment variables.

Malformed environment variables are silently ignored.

Malformed environment variables are silently ignored.

@menu

@menu

* GFORTRAN_STDIN_UNIT:: Unit number for standard input

* GFORTRAN_STDIN_UNIT:: Unit number for standard input

* GFORTRAN_STDOUT_UNIT:: Unit number for standard output

* GFORTRAN_STDOUT_UNIT:: Unit number for standard output

* GFORTRAN_STDERR_UNIT:: Unit number for standard error

* GFORTRAN_STDERR_UNIT:: Unit number for standard error

* GFORTRAN_USE_STDERR:: Send library output to standard error

* GFORTRAN_USE_STDERR:: Send library output to standard error

* GFORTRAN_TMPDIR:: Directory for scratch files

* GFORTRAN_TMPDIR:: Directory for scratch files

* GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.

* GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.

* GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.

* GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.

* GFORTRAN_SHOW_LOCUS::  Show location for runtime errors

* GFORTRAN_SHOW_LOCUS::  Show location for runtime errors

* GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted

* GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted

* GFORTRAN_DEFAULT_RECL:: Default record length for new files

* GFORTRAN_DEFAULT_RECL:: Default record length for new files

* GFORTRAN_LIST_SEPARATOR::  Separator for list output

* GFORTRAN_LIST_SEPARATOR::  Separator for list output

* GFORTRAN_CONVERT_UNIT::  Set endianness for unformatted I/O

* GFORTRAN_CONVERT_UNIT::  Set endianness for unformatted I/O

* GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors

* GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors

* GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors

* GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors

@end menu

@end menu

@node GFORTRAN_STDIN_UNIT

@node GFORTRAN_STDIN_UNIT

@section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input

@section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input

This environment variable can be used to select the unit number

This environment variable can be used to select the unit number

preconnected to standard input.  This must be a positive integer.

preconnected to standard input.  This must be a positive integer.

The default value is 5.

The default value is 5.

@node GFORTRAN_STDOUT_UNIT

@node GFORTRAN_STDOUT_UNIT

@section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output

@section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output

This environment variable can be used to select the unit number

This environment variable can be used to select the unit number

preconnected to standard output.  This must be a positive integer.

preconnected to standard output.  This must be a positive integer.

The default value is 6.

The default value is 6.

@node GFORTRAN_STDERR_UNIT

@node GFORTRAN_STDERR_UNIT

@section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error

@section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error

This environment variable can be used to select the unit number

This environment variable can be used to select the unit number

preconnected to standard error.  This must be a positive integer.

preconnected to standard error.  This must be a positive integer.

The default value is 0.

The default value is 0.

@node GFORTRAN_USE_STDERR

@node GFORTRAN_USE_STDERR

@section @env{GFORTRAN_USE_STDERR}---Send library output to standard error

@section @env{GFORTRAN_USE_STDERR}---Send library output to standard error

This environment variable controls where library output is sent.

This environment variable controls where library output is sent.

If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard

If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard

error is used. If the first letter is @samp{n}, @samp{N} or

error is used. If the first letter is @samp{n}, @samp{N} or

@samp{0}, standard output is used.

@samp{0}, standard output is used.

@node GFORTRAN_TMPDIR

@node GFORTRAN_TMPDIR

@section @env{GFORTRAN_TMPDIR}---Directory for scratch files

@section @env{GFORTRAN_TMPDIR}---Directory for scratch files

This environment variable controls where scratch files are

This environment variable controls where scratch files are

created.  If this environment variable is missing,

created.  If this environment variable is missing,

GNU Fortran searches for the environment variable @env{TMP}.  If

GNU Fortran searches for the environment variable @env{TMP}.  If

this is also missing, the default is @file{/tmp}.

this is also missing, the default is @file{/tmp}.

@node GFORTRAN_UNBUFFERED_ALL

@node GFORTRAN_UNBUFFERED_ALL

@section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units

@section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units

This environment variable controls whether all I/O is unbuffered.  If

This environment variable controls whether all I/O is unbuffered.  If

the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is

the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is

unbuffered. This will slow down small sequential reads and writes.  If

unbuffered. This will slow down small sequential reads and writes.  If

the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.

the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.

This is the default.

This is the default.

@node GFORTRAN_UNBUFFERED_PRECONNECTED

@node GFORTRAN_UNBUFFERED_PRECONNECTED

@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units

@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units

The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls

The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls

whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered.  If

whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered.  If

the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This

the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This

will slow down small sequential reads and writes.  If the first letter

will slow down small sequential reads and writes.  If the first letter

is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.  This is the default.

is @samp{n}, @samp{N} or @samp{0}, I/O is buffered.  This is the default.

@node GFORTRAN_SHOW_LOCUS

@node GFORTRAN_SHOW_LOCUS

@section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors

@section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors

If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and

If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and

line numbers for runtime errors are printed.  If the first letter is

line numbers for runtime errors are printed.  If the first letter is

@samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers

@samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers

for runtime errors. The default is to print the location.

for runtime errors. The default is to print the location.

@node GFORTRAN_OPTIONAL_PLUS

@node GFORTRAN_OPTIONAL_PLUS

@section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted

@section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted

If the first letter is @samp{y}, @samp{Y} or @samp{1},

If the first letter is @samp{y}, @samp{Y} or @samp{1},

a plus sign is printed

a plus sign is printed

where permitted by the Fortran standard.  If the first letter

where permitted by the Fortran standard.  If the first letter

is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed

is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed

in most cases. Default is not to print plus signs.

in most cases. Default is not to print plus signs.

@node GFORTRAN_DEFAULT_RECL

@node GFORTRAN_DEFAULT_RECL

@section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files

@section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files

This environment variable specifies the default record length, in

This environment variable specifies the default record length, in

bytes, for files which are opened without a @code{RECL} tag in the

bytes, for files which are opened without a @code{RECL} tag in the

@code{OPEN} statement.  This must be a positive integer.  The

@code{OPEN} statement.  This must be a positive integer.  The

default value is 1073741824 bytes (1 GB).

default value is 1073741824 bytes (1 GB).

@node GFORTRAN_LIST_SEPARATOR

@node GFORTRAN_LIST_SEPARATOR

@section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output

@section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output

This environment variable specifies the separator when writing

This environment variable specifies the separator when writing

list-directed output.  It may contain any number of spaces and

list-directed output.  It may contain any number of spaces and

at most one comma.  If you specify this on the command line,

at most one comma.  If you specify this on the command line,

be sure to quote spaces, as in

be sure to quote spaces, as in

@smallexample

@smallexample

$ GFORTRAN_LIST_SEPARATOR='  ,  ' ./a.out

$ GFORTRAN_LIST_SEPARATOR='  ,  ' ./a.out

@end smallexample

@end smallexample

when @command{a.out} is the compiled Fortran program that you want to run.

when @command{a.out} is the compiled Fortran program that you want to run.

Default is a single space.

Default is a single space.

@node GFORTRAN_CONVERT_UNIT

@node GFORTRAN_CONVERT_UNIT

@section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O

@section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O

By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible

By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible

to change the representation of data for unformatted files.

to change the representation of data for unformatted files.

The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:

The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:

@smallexample

@smallexample

GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;

GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;

mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;

mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;

exception: mode ':' unit_list | unit_list ;

exception: mode ':' unit_list | unit_list ;

unit_list: unit_spec | unit_list unit_spec ;

unit_list: unit_spec | unit_list unit_spec ;

unit_spec: INTEGER | INTEGER '-' INTEGER ;

unit_spec: INTEGER | INTEGER '-' INTEGER ;

@end smallexample

@end smallexample

The variable consists of an optional default mode, followed by

The variable consists of an optional default mode, followed by

a list of optional exceptions, which are separated by semicolons

a list of optional exceptions, which are separated by semicolons

from the preceding default and each other.  Each exception consists

from the preceding default and each other.  Each exception consists

of a format and a comma-separated list of units.  Valid values for

of a format and a comma-separated list of units.  Valid values for

the modes are the same as for the @code{CONVERT} specifier:

the modes are the same as for the @code{CONVERT} specifier:

@itemize @w{}

@itemize @w{}

@item @code{NATIVE} Use the native format.  This is the default.

@item @code{NATIVE} Use the native format.  This is the default.

@item @code{SWAP} Swap between little- and big-endian.

@item @code{SWAP} Swap between little- and big-endian.

@item @code{LITTLE_ENDIAN} Use the little-endian format

@item @code{LITTLE_ENDIAN} Use the little-endian format

for unformatted files.

for unformatted files.

@item @code{BIG_ENDIAN} Use the big-endian format for unformatted files.

@item @code{BIG_ENDIAN} Use the big-endian format for unformatted files.

@end itemize

@end itemize

A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.

A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.

Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:

Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:

@itemize @w{}

@itemize @w{}

@item @code{'big_endian'}  Do all unformatted I/O in big_endian mode.

@item @code{'big_endian'}  Do all unformatted I/O in big_endian mode.

@item @code{'little_endian;native:10-20,25'}  Do all unformatted I/O

@item @code{'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

in little_endian mode, except for units 10 to 20 and 25, which are in

native format.

native format.

@item @code{'10-20'}  Units 10 to 20 are big-endian, the rest is native.

@item @code{'10-20'}  Units 10 to 20 are big-endian, the rest is native.

@end itemize

@end itemize

Setting the environment variables should be done on the command

Setting the environment variables should be done on the command

line or via the @command{export}

line or via the @command{export}

command for @command{sh}-compatible shells and via @command{setenv}

command for @command{sh}-compatible shells and via @command{setenv}

for @command{csh}-compatible shells.

for @command{csh}-compatible shells.

Example for @command{sh}:

Example for @command{sh}:

@smallexample

@smallexample

$ gfortran foo.f90

$ gfortran foo.f90

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

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

@end smallexample

@end smallexample

Example code for @command{csh}:

Example code for @command{csh}:

@smallexample

@smallexample

% gfortran foo.f90

% gfortran foo.f90

% setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'

% setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'

% ./a.out

% ./a.out

@end smallexample

@end smallexample

Using anything but the native representation for unformatted data

Using anything but the native representation for unformatted data

carries a significant speed overhead.  If speed in this area matters

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

to you, it is best if you use this only for data that needs to be

portable.

portable.

@xref{CONVERT specifier}, for an alternative way to specify the

@xref{CONVERT specifier}, for an alternative way to specify the

data representation for unformatted files.  @xref{Runtime Options}, for

data representation for unformatted files.  @xref{Runtime Options}, for

setting a default data representation for the whole program.  The

setting a default data representation for the whole program.  The

@code{CONVERT} specifier overrides the @option{-fconvert} compile options.

@code{CONVERT} specifier overrides the @option{-fconvert} compile options.

@emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT

@emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT

environment variable will override the CONVERT specifier in the

environment variable will override the CONVERT specifier in the

open statement}.  This is to give control over data formats to

open statement}.  This is to give control over data formats to

users who do not have the source code of their program available.

users who do not have the source code of their program available.

@node GFORTRAN_ERROR_DUMPCORE

@node GFORTRAN_ERROR_DUMPCORE

@section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors

@section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors

If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to

If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to

@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)

@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)

then library run-time errors cause core dumps. To disable the core

then library run-time errors cause core dumps. To disable the core

dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default

dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default

is not to core dump unless the @option{-fdump-core} compile option

is not to core dump unless the @option{-fdump-core} compile option

was used.

was used.

@node GFORTRAN_ERROR_BACKTRACE

@node GFORTRAN_ERROR_BACKTRACE

@section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors

@section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors

If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to

If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to

@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)

@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)

then a backtrace is printed when a run-time error occurs.

then a backtrace is printed when a run-time error occurs.

To disable the backtracing, set the variable to

To disable the backtracing, set the variable to

@samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace

@samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace

unless the @option{-fbacktrace} compile option

unless the @option{-fbacktrace} compile option

was used.

was used.

@c =====================================================================

@c =====================================================================

@c PART II: LANGUAGE REFERENCE

@c PART II: LANGUAGE REFERENCE

@c =====================================================================

@c =====================================================================

@tex

@tex

\part{II}{Language Reference}

\part{II}{Language Reference}

@end tex

@end tex

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@c Fortran 2003 and 2008 Status

@c Fortran 2003 and 2008 Status

@c ---------------------------------------------------------------------

@c ---------------------------------------------------------------------

@node Fortran 2003 and 2008 status

@node Fortran 2003 and 2008 status

@chapter Fortran 2003 and 2008 Status

@chapter Fortran 2003 and 2008 Status

@menu

@menu

* Fortran 2003 status::

* Fortran 2003 status::

* Fortran 2008 status::

* Fortran 2008 status::

@end menu

@end menu

@node Fortran 2003 status

@node Fortran 2003 status

@section Fortran 2003 status

@section Fortran 2003 status

GNU Fortran supports several Fortran 2003 features; an incomplete

GNU Fortran supports several Fortran 2003 features; an incomplete

list can be found below.  See also the

list can be found below.  See also the

@uref{http://gcc.gnu.org/wiki/Fortran2003, wiki page} about Fortran 2003.

@uref{http://gcc.gnu.org/wiki/Fortran2003, wiki page} about Fortran 2003.

@itemize

@itemize

@item

@item

Intrinsics @code{command_argument_count}, @code{get_command},

Intrinsics @code{command_argument_count}, @code{get_command},

@code{get_command_argument}, @code{get_environment_variable}, and

@code{get_command_argument}, @code{get_environment_variable}, and

@code{move_alloc}.

@code{move_alloc}.

@item

@item

@cindex array, constructors

@cindex array, constructors

@cindex @code{[...]}

@cindex @code{[...]}

Array constructors using square brackets. That is, @code{[...]} rather

Array constructors using square brackets. That is, @code{[...]} rather

than @code{(/.../)}.  Type-specification for array constructors like

than @code{(/.../)}.  Type-specification for array constructors like

@code{(/ some-type :: ... /)}.

@code{(/ some-type :: ... /)}.

@item

@item

@cindex @code{FLUSH} statement

@cindex @code{FLUSH} statement

@cindex statement, @code{FLUSH}

@cindex statement, @code{FLUSH}

@code{FLUSH} statement.

@code{FLUSH} statement.

@item

@item

@cindex @code{IOMSG=} specifier

@cindex @code{IOMSG=} specifier

@code{IOMSG=} specifier for I/O statements.

@code{IOMSG=} specifier for I/O statements.

@item

@item

@cindex @code{ENUM} statement

@cindex @code{ENUM} statement

@cindex @code{ENUMERATOR} statement

@cindex @code{ENUMERATOR} statement

@cindex statement, @code{ENUM}

@cindex statement, @code{ENUM}

@cindex statement, @code{ENUMERATOR}

@cindex statement, @code{ENUMERATOR}

@opindex @code{fshort-enums}

@opindex @code{fshort-enums}

Support for the declaration of enumeration constants via the

Support for the declaration of enumeration constants via the

@code{ENUM} and @code{ENUMERATOR} statements.  Interoperability with

@code{ENUM} and @code{ENUMERATOR} statements.  Interoperability with

@command{gcc} is guaranteed also for the case where the

@command{gcc} is guaranteed also for the case where the

@command{-fshort-enums} command line option is given.

@command{-fshort-enums} command line option is given.

@item

@item

@cindex TR 15581

@cindex TR 15581

TR 15581:

TR 15581:

@itemize

@itemize

@item

@item

@cindex @code{ALLOCATABLE} dummy arguments

@cindex @code{ALLOCATABLE} dummy arguments

@code{ALLOCATABLE} dummy arguments.

@code{ALLOCATABLE} dummy arguments.

@item

@item

@cindex @code{ALLOCATABLE} function results

@cindex @code{ALLOCATABLE} function results

@code{ALLOCATABLE} function results

@code{ALLOCATABLE} function results

@item

@item

@cindex @code{ALLOCATABLE} components of derived types

@cindex @code{ALLOCATABLE} components of derived types

@code{ALLOCATABLE} components of derived types

@code{ALLOCATABLE} components of derived types

@end itemize

@end itemize

@item

@item

@cindex @code{ALLOCATE}

@cindex @code{ALLOCATE}

The @code{ERRMSG=} tag is now supported in @code{ALLOCATE} and

The @code{ERRMSG=} tag is now supported in @code{ALLOCATE} and

@code{DEALLOCATE} statements.  The @code{SOURCE=} tag is supported

@code{DEALLOCATE} statements.  The @code{SOURCE=} tag is supported

in an @code{ALLOCATE} statement.  An @emph{intrinsic-type-spec}

in an @code{ALLOCATE} statement.  An @emph{intrinsic-type-spec}

can be used as the @emph{type-spec} in an @code{ALLOCATE} statement;

can be used as the @emph{type-spec} in an @code{ALLOCATE} statement;

while the use of a @emph{derived-type-name} is currently unsupported.

while the use of a @emph{derived-type-name} is currently unsupported.

@item

@item

@cindex @code{STREAM} I/O

@cindex @code{STREAM} I/O

@cindex @code{ACCESS='STREAM'} I/O

@cindex @code{ACCESS='STREAM'} I/O

The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,

The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,

allowing I/O without any record structure.

allowing I/O without any record structure.

@item

@item

Namelist input/output for internal files.

Namelist input/output for internal files.

@item

@item

@cindex @code{PROTECTED} statement

@cindex @code{PROTECTED} statement

@cindex statement, @code{PROTECTED}

@cindex statement, @code{PROTECTED}

The @code{PROTECTED} statement and attribute.

The @code{PROTECTED} statement and attribute.

@item

@item

@cindex @code{VALUE} statement

@cindex @code{VALUE} statement

@cindex statement, @code{VALUE}

@cindex statement, @code{VALUE}

The @code{VALUE} statement and attribute.

The @code{VALUE} statement and attribute.

@item

@item

@cindex @code{VOLATILE} statement

@cindex @code{VOLATILE} statement

@cindex statement, @code{VOLATILE}

@cindex statement, @code{VOLATILE}

The @code{VOLATILE} statement and attribute.

The @code{VOLATILE} statement and attribute.

@item

@item

@cindex @code{IMPORT} statement

@cindex @code{IMPORT} statement

@cindex statement, @code{IMPORT}

@cindex statement, @code{IMPORT}

The @code{IMPORT} statement, allowing to import

The @code{IMPORT} statement, allowing to import

host-associated derived types.

host-associated derived types.

@item

@item

@cindex @code{USE, INTRINSIC} statement

@cindex @code{USE, INTRINSIC} statement

@cindex statement, @code{USE, INTRINSIC}

@cindex statement, @code{USE, INTRINSIC}

@cindex @code{ISO_FORTRAN_ENV} statement

@cindex @code{ISO_FORTRAN_ENV} statement

@cindex statement, @code{ISO_FORTRAN_ENV}

@cindex statement, @code{ISO_FORTRAN_ENV}

@code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}

@code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}

attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},

attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},

@code{OMP_LIB} and @code{OMP_LIB_KINDS}.

@code{OMP_LIB} and @code{OMP_LIB_KINDS}.

@item

@item

Renaming of operators in the @code{USE} statement.

Renaming of operators in the @code{USE} statement.

@item

@item

@cindex ISO C Bindings

@cindex ISO C Bindings

Interoperability with C (ISO C Bindings)

Interoperability with C (ISO C Bindings)

@item

@item

BOZ as argument of @code{INT}, @code{REAL}, @code{DBLE} and @code{CMPLX}.

BOZ as argument of @code{INT}, @code{REAL}, @code{DBLE} and @code{CMPLX}.

@item

@item

@cindex type-bound procedure

@cindex type-bound procedure

@cindex type-bound operator

@cindex type-bound operator

Type-bound procedures with @code{PROCEDURE} or @code{GENERIC}, and operators

Type-bound procedures with @code{PROCEDURE} or @code{GENERIC}, and operators

bound to a derived-type.

bound to a derived-type.

@item

@item

@cindex @code{EXTENDS}

@cindex @code{EXTENDS}

@cindex derived-type extension

@cindex derived-type extension

Extension of derived-types (the @code{EXTENDS(...)} syntax).

Extension of derived-types (the @code{EXTENDS(...)} syntax).

@item

@item

@cindex @code{ABSTRACT} type

@cindex @code{ABSTRACT} type

@cindex @code{DEFERRED} procedure binding

@cindex @code{DEFERRED} procedure binding

@code{ABSTRACT} derived-types and declaring procedure bindings @code{DEFERRED}.

@code{ABSTRACT} derived-types and declaring procedure bindings @code{DEFERRED}.

@end itemize

@end itemize

@node Fortran 2008 status

@node Fortran 2008 status

@section Fortran 2008 status

@section Fortran 2008 status