\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename gfortran.info
-@set copyrights-gfortran 1999-2006
+@set copyrights-gfortran 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
@include gcc-common.texi
-@settitle The GNU Fortran 95 Compiler
+@settitle The GNU Fortran Compiler
@c Create a separate index for command line options
@defcodeindex op
@syncodeindex pg cp
@syncodeindex tp cp
+@c TODO: The following "Part" definitions are included here temporarily
+@c until they are incorporated into the official Texinfo distribution.
+@c They borrow heavily from Texinfo's \unnchapentry definitions.
+
+@tex
+\gdef\part#1#2{%
+ \pchapsepmacro
+ \gdef\thischapter{}
+ \begingroup
+ \vglue\titlepagetopglue
+ \titlefonts \rm
+ \leftline{Part #1:@* #2}
+ \vskip4pt \hrule height 4pt width \hsize \vskip4pt
+ \endgroup
+ \writetocentry{part}{#2}{#1}
+}
+\gdef\blankpart{%
+ \writetocentry{blankpart}{}{}
+}
+% Part TOC-entry definition for summary contents.
+\gdef\dosmallpartentry#1#2#3#4{%
+ \vskip .5\baselineskip plus.2\baselineskip
+ \begingroup
+ \let\rm=\bf \rm
+ \tocentry{Part #2: #1}{\doshortpageno\bgroup#4\egroup}
+ \endgroup
+}
+\gdef\dosmallblankpartentry#1#2#3#4{%
+ \vskip .5\baselineskip plus.2\baselineskip
+}
+% Part TOC-entry definition for regular contents. This has to be
+% equated to an existing entry to not cause problems when the PDF
+% outline is created.
+\gdef\dopartentry#1#2#3#4{%
+ \unnchapentry{Part #2: #1}{}{#3}{#4}
+}
+\gdef\doblankpartentry#1#2#3#4{}
+@end tex
+
@c %**end of header
@c Use with @@smallbook.
Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.1 or
+under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
-Invariant Sections being ``GNU General Public License'' and ``Funding
-Free Software'', the Front-Cover
-texts being (a) (see below), and with the Back-Cover Texts being (b)
+Invariant Sections being ``Funding Free Software'', the Front-Cover
+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
``GNU Free Documentation License''.
@end copying
@ifinfo
-@dircategory Programming
+@dircategory Software development
@direntry
-* gfortran: (gfortran). The GNU Fortran 95 Compiler.
+* gfortran: (gfortran). The GNU Fortran Compiler.
@end direntry
This file documents the use and the internals of
-the GNU Fortran 95 compiler, (@command{gfortran}).
+the GNU Fortran compiler, (@command{gfortran}).
Published by the Free Software Foundation
51 Franklin Street, Fifth Floor
@setchapternewpage odd
@titlepage
-@title Using GNU Fortran 95
-@sp 2
-@center The gfortran team
+@title Using GNU Fortran
+@versionsubtitle
+@author The @t{gfortran} team
@page
@vskip 0pt plus 1filll
-For the @value{version-GCC} Version*
-@sp 1
-Published by the Free Software Foundation @*
+Published by the Free Software Foundation@*
51 Franklin Street, Fifth Floor@*
Boston, MA 02110-1301, USA@*
@c Last printed ??ber, 19??.@*
@sp 1
@insertcopying
@end titlepage
+
+@c TODO: The following "Part" definitions are included here temporarily
+@c until they are incorporated into the official Texinfo distribution.
+
+@tex
+\global\let\partentry=\dosmallpartentry
+\global\let\blankpartentry=\dosmallblankpartentry
+@end tex
@summarycontents
+
+@tex
+\global\let\partentry=\dopartentry
+\global\let\blankpartentry=\doblankpartentry
+@end tex
@contents
+
@page
+@c ---------------------------------------------------------------------
+@c TexInfo table of contents.
+@c ---------------------------------------------------------------------
+
+@ifnottex
@node Top
@top Introduction
@cindex Introduction
This manual documents the use of @command{gfortran},
-the GNU Fortran 95 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.
@ifset DEVELOPMENT
@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
-not accurately reflect the status of the most recent @command{gfortran}.
+not accurately reflect the status of the most recent GNU Fortran compiler.
@end ifset
@comment
@comment better formatting.
@comment
@menu
-* Getting Started:: What you should know about @command{gfortran}.
-* GFORTRAN and GCC:: You can compile Fortran, C, or other programs.
-* GFORTRAN and G77:: Why we chose to start from scratch.
-* Invoking GFORTRAN:: Command options supported by @command{gfortran}.
-* Project Status:: Status of @command{gfortran}, roadmap, proposed extensions.
-* Contributing:: How you can help.
-* Standards:: Standards supported by @command{gfortran}
+* Introduction::
+
+Part I: Invoking GNU Fortran
+* Invoking GNU Fortran:: Command options supported by @command{gfortran}.
* Runtime:: Influencing runtime behavior with environment variables.
-* Extensions:: Language extensions implemented by @command{gfortran}
-* Intrinsic Procedures:: Intrinsic procedures supported by @command{gfortran}
+
+Part II: Language Reference
+* Fortran 2003 and 2008 status:: Fortran 2003 and 2008 features supported by GNU Fortran.
+* Compiler Characteristics:: User-visible implementation details.
+* Mixed-Language Programming:: Interoperability with C
+* Extensions:: Language extensions implemented by GNU Fortran.
+* Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran.
+* Intrinsic Modules:: Intrinsic modules supported by GNU Fortran.
+
+* Contributing:: How you can help.
* Copying:: GNU General Public License says
how you can copy and share GNU Fortran.
* 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.
-* Index:: Index of this documentation.
+* Option Index:: Index of command line options
+* Keyword Index:: Index of concepts
@end menu
-
-
+@end ifnottex
@c ---------------------------------------------------------------------
-@c Getting Started
+@c Introduction
@c ---------------------------------------------------------------------
-@node Getting Started
-@chapter Getting Started
+@node Introduction
+@chapter Introduction
-Gfortran is the GNU Fortran 95 compiler front end,
+@c The following duplicates the text on the TexInfo table of contents.
+@iftex
+This manual documents the use of @command{gfortran}, the GNU Fortran
+compiler. You can find in this manual how to invoke @command{gfortran},
+as well as its features and incompatibilities.
+
+@ifset DEVELOPMENT
+@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 not accurately reflect the status of the most recent GNU Fortran
+compiler.
+@end ifset
+@end iftex
+
+The GNU Fortran compiler front end was
designed initially as a free replacement for,
or alternative to, the unix @command{f95} command;
@command{gfortran} is the command you'll use to invoke the compiler.
-Gfortran is still in an early state of development.
-@command{gfortran} can generate code for most constructs and expressions,
-but much work remains to be done.
+@menu
+* About GNU Fortran:: What you should know about the GNU Fortran compiler.
+* GNU Fortran and GCC:: You can compile Fortran, C, or other programs.
+* Preprocessing and conditional compilation:: The Fortran preprocessor
+* GNU Fortran and G77:: Why we chose to start from scratch.
+* Project Status:: Status of GNU Fortran, roadmap, proposed extensions.
+* Standards:: Standards supported by GNU Fortran.
+@end menu
+
-When @command{gfortran} is finished,
-it will do everything you expect from any decent compiler:
+@c ---------------------------------------------------------------------
+@c About GNU Fortran
+@c ---------------------------------------------------------------------
+
+@node About GNU Fortran
+@section About GNU Fortran
+
+The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards
+completely, parts of the Fortran 2003 and Fortran 2008 standards, and
+several vendor extensions. The development goal is to provide the
+following features:
@itemize @bullet
@item
Read a user's program,
stored in a file and containing instructions written
-in Fortran 77, Fortran 90 or Fortran 95.
+in Fortran 77, Fortran 90, Fortran 95, Fortran 2003 or Fortran 2008.
This file contains @dfn{source code}.
@item
by a machine such as your computer.
Humans usually aren't as good writing machine code
as they are at writing Fortran (or C++, Ada, or Java),
-because is easy to make tiny mistakes writing machine code.
+because it is easy to make tiny mistakes writing machine code.
@item
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.
-When writing Fortran, it is easy to make big mistakes.
-The Fortran 90 requires that the compiler can point out
+The Fortran 90 standard requires that the compiler can point out
mistakes to the user.
An incorrect usage of the language causes an @dfn{error message}.
and @dfn{linked} to the user program.
@end itemize
-Gfortran consists of several components:
+The GNU Fortran compiler consists of several components:
@itemize @bullet
@item
which also might be installed as the
system's @command{f95} command.
@command{gfortran} is just another driver program,
-but specifically for the Fortran 95 compiler only.
+but specifically for the Fortran compiler only.
The difference with @command{gcc} is that @command{gfortran}
will automatically link the correct libraries to your program.
@item
The Fortran compiler itself, (@command{f951}).
-This is the gfortran parser and code generator,
+This is the GNU Fortran parser and code generator,
linked to and interfaced with the GCC backend library.
@command{f951} ``translates'' the source code to
assembler code. You would typically not use this
@end itemize
-
@c ---------------------------------------------------------------------
-@c GFORTRAN and GCC
+@c GNU Fortran and GCC
@c ---------------------------------------------------------------------
-@node GFORTRAN and GCC
-@chapter GFORTRAN and GCC
+@node GNU Fortran and GCC
+@section GNU Fortran and GCC
@cindex GNU Compiler Collection
+@cindex 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
+translate the source code into a language-independent form called
+@dfn{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 (@command{gcc})
+which provides the command-line interface for the compiler. It calls
+the relevant compiler front-end program (e.g., @command{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,
+@command{gcc} will recognize files with @file{.f}, @file{.for}, @file{.ftn},
+@file{.f90}, @file{.f95}, @file{.f03} and @file{.f08} extensions as
+Fortran source code, and compile it accordingly. A @command{gfortran}
+driver program is also provided, which is identical to @command{gcc}
+except that it automatically links the Fortran runtime libraries into the
+compiled program.
+
+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.
+Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.f08},
+@file{.F90}, @file{.F95}, @file{.F03} and @file{.F08} extensions are
+treated as free form. The capitalized versions of either form are run
+through preprocessing. Source files with the lower case @file{.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
+@ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}.
+The two manuals together provide a complete reference for the GNU
+Fortran compiler.
+
-GCC used to be the GNU ``C'' Compiler,
-but is now known as the @dfn{GNU Compiler Collection}.
-GCC provides the GNU system with a very versatile
-compiler middle end (shared optimization passes),
-and back ends (code generators) for many different
-computer architectures and operating systems.
-The code of the middle end and back end are shared by all
-compiler front ends that are in the GNU Compiler Collection.
-
-A GCC front end is essentially a source code parser
-and an intermediate code generator. The code generator translates the
-semantics of the source code into a language independent form called
-@dfn{GENERIC}.
-
-The parser takes a source file written in a
-particular computer language, reads and parses it,
-and tries to make sure that the source code conforms to
-the language rules.
-Once the correctness of a program has been established,
-the compiler will build a data structure known as the
-@dfn{Abstract Syntax tree},
-or just @dfn{AST} or ``tree'' for short.
-This data structure represents the whole program
-or a subroutine or a function.
-The ``tree'' is passed to the GCC middle end,
-which will perform optimization passes on it. The optimized AST is then
-handed off too the back end which assembles the program unit.
-
-Different phases in this translation process can be,
-and in fact @emph{are} merged in many compiler front ends.
-GNU Fortran 95 has a strict separation between the
-parser and code generator.
-
-The goal of the gfortran project is to build a new front end for GCC.
-Specifically, a Fortran 95 front end.
-In a non-gfortran installation,
-@command{gcc} will not be able to compile Fortran 95 source code
-(only the ``C'' front end has to be compiled if you want to build GCC,
-all other languages are optional).
-If you build GCC with gfortran, @command{gcc} will recognize
-@file{.f/.f90/.f95} source files and accepts Fortran 95 specific
-command line options.
+@c ---------------------------------------------------------------------
+@c Preprocessing and conditional compilation
+@c ---------------------------------------------------------------------
+@node Preprocessing and conditional compilation
+@section Preprocessing and conditional compilation
+@cindex CPP
+@cindex FPP
+@cindex Conditional compilation
+@cindex Preprocessing
+@cindex preprocessor, include file handling
+
+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 @file{.F}, @file{.FOR}, @file{.FTN}, @file{.fpp},
+@file{.FPP}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. To manually
+invoke the preprocessor on any file, use @option{-cpp}, to disable
+preprocessing on files where the preprocessor is run automatically, use
+@option{-nocpp}.
+
+If a preprocessed file includes another file with the Fortran @code{INCLUDE}
+statement, the included file is not preprocessed. To preprocess included
+files, use the equivalent preprocessor statement @code{#include}.
+
+If GNU Fortran invokes the preprocessor, @code{__GFORTRAN__}
+is defined and @code{__GNUC__}, @code{__GNUC_MINOR__} and
+@code{__GNUC_PATCHLEVEL__} can be used to determine the version of the
+compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details.
+
+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 (@uref{http://www.daniellnagle.com/coco.html}).
@c ---------------------------------------------------------------------
-@c GFORTRAN and G77
+@c GNU Fortran and G77
@c ---------------------------------------------------------------------
-@node GFORTRAN and G77
-@chapter GFORTRAN and G77
+@node GNU Fortran and G77
+@section GNU Fortran and G77
@cindex Fortran 77
-@cindex G77
-
-Why do we write a compiler front end from scratch?
-There's a fine Fortran 77 compiler in the
-GNU Compiler Collection that accepts some features
-of the Fortran 90 standard as extensions.
-Why not start from there and revamp it?
-
-One of the reasons is that Craig Burley, the author of G77,
-has decided to stop working on the G77 front end.
-On @uref{http://world.std.com/~burley/g77-why.html,
-Craig explains the reasons for his decision to stop working on G77}
-in one of the pages in his homepage.
-Among the reasons is a lack of interest in improvements to
-@command{g77}.
-Users appear to be quite satisfied with @command{g77} as it is.
-While @command{g77} is still being maintained (by Toon Moene),
-it is unlikely that sufficient people will be willing
-to completely rewrite the existing code.
-
-But there are other reasons to start from scratch.
-Many people, including Craig Burley,
-no longer agreed with certain design decisions in the G77 front end.
-Also, the interface of @command{g77} to the back end is written in
-a style which is confusing and not up to date on recommended practice.
-In fact, a full rewrite had already been planned for GCC 3.0.
-
-When Craig decided to stop,
-it just seemed to be a better idea to start a new project from scratch,
-because it was expected to be easier to maintain code we
-develop ourselves than to do a major overhaul of @command{g77} first,
-and then build a Fortran 95 compiler out of it.
+@cindex @command{g77}
+
+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
+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 @command{g77}.
-@include invoke.texi
@c ---------------------------------------------------------------------
@c Project Status
@c ---------------------------------------------------------------------
@node Project Status
-@chapter Project Status
+@section Project Status
@quotation
-As soon as 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.
When we generate code, the ``puppa'' state.
-When gfortran is done,
+When @command{gfortran} is done,
we'll see if it will be a beautiful butterfly,
or just a big bug....
(even though Andy had already been working on it for a while,
of course).
-Gfortran is currently reaching the stage where is is able to compile real
-world programs. However it is still under development and has many rough
-edges.
-
-@menu
-* Compiler Status::
-* Library Status::
-* Proposed Extensions::
-@end menu
-
-@node Compiler Status
-@section Compiler Status
-
-@table @emph
-@item Front end
-This is the part of gfortran which parses a source file, verifies that it
-is valid Fortran 95, performs compile time replacement of constants
-(PARAMETER variables) and reads and generate module files. This is
-almost complete. Every Fortran 95 source should be accepted, and most
-none-Fortran 95 source should be rejected. If you find a source file where
-this is not true, please tell us. You can use the -fsyntax-only switch to
-make gfortran quit after running the front end, effectively reducing it to
-a syntax checker.
-
-@item Middle end interface
-These are the parts of gfortran that take the parse tree generated by the
-front end and translate it to the GENERIC form required by the GCC back
-end. Work is ongoing in these parts of gfortran, but a large part has
-already been completed.
-@end table
-
-@node Library Status
-@section Library Status
-
-Some intrinsic functions map directly to library functions, and in most
-cases the name of the library function used depends on the type of the
-arguments. For some intrinsics we generate inline code, and for others,
-such as sin, cos and sqrt, we rely on the backend to use special
-instructions in the floating point unit of the CPU if available, or to
-fall back to a call to libm if these are not available.
-
-Implementation of some non-elemental intrinsic functions (eg. DOT_PRODUCT,
-AVERAGE) is not yet optimal. This is hard because we have to make decisions
-whether to use inline code (good for small arrays as no function call
-overhead occurs) or generate function calls (good for large arrays as it
-allows use of hand-optimized assembly routines, SIMD instructions, etc.)
-
-The IO library is in a mostly usable state. Unformatted I/O for
-@code{REAL(KIND=10)} variables is currently not recommended.
-
-Array intrinsics mostly work.
-
-@node Proposed Extensions
-@section Proposed Extensions
-
-Here's a list of proposed extensions for @command{gfortran}, in no particular
-order. Most of these are necessary to be fully compatible with
-existing Fortran compilers, but they are not part of the official
-J3 Fortran 95 standard.
-
-@subsection Compiler extensions:
-@itemize @bullet
-@item
-Flag for defining the kind number for default logicals.
-
-@item
-User-specified alignment rules for structures.
-@item
-Flag to generate @code{Makefile} info.
-
-@item
-Automatically extend single precision constants to double.
-
-@item
-Compile code that conserves memory by dynamically allocating common and
-module storage either on stack or heap.
-
-@item
-Flag to cause the compiler to distinguish between upper and lower case
-names. The Fortran 95 standard does not distinguish them.
-
-@item
-Compile flag to generate code for array conformance checking (suggest -CC).
-
-@item
-User control of symbol names (underscores, etc).
-
-@item
-Compile setting for maximum size of stack frame size before spilling
-parts to static or heap.
-
-@item
-Flag to force local variables into static space.
-
-@item
-Flag to force local variables onto stack.
-
-@item
-Flag to compile lines beginning with ``D''.
-
-@item
-Flag to ignore lines beginning with ``D''.
-
-@item
-Flag for maximum errors before ending compile.
-
-@item
-Generate code to check for null pointer dereferences -- prints locus of
-dereference instead of segfaulting. There was some discussion about this
-option in the g95 development mailing list.
+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, and several Fortran 2003 and Fortran
+2008 features, including TR 15581. However, it is still under
+development and has a few remaining rough edges.
+
+At present, the GNU Fortran compiler passes the
+@uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html,
+NIST Fortran 77 Test Suite}, and produces acceptable results on the
+@uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}.
+It also provides respectable performance on
+the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran
+compiler benchmarks} and the
+@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
+large real-world programs, including
+@uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM
+weather-forecasting code} and
+@uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum
+chemistry package}; see @url{http://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 and Fortran 2008.
-@item
-Allow setting the default unit number.
-@item
-Option to initialize otherwise uninitialized integer and floating
-point variables.
+@c ---------------------------------------------------------------------
+@c Standards
+@c ---------------------------------------------------------------------
-@item
-Support for Fortran 200x. This includes several new features including
-floating point exceptions, extended use of allocatable arrays, C
-interoperability, Parameterizer data types and function pointers.
-@end itemize
+@node Standards
+@section Standards
+@cindex Standards
+@menu
+* Varying Length Character Strings::
+@end menu
-@subsection Environment Options
-@itemize @bullet
-@item
-Pluggable library modules for random numbers, linear algebra.
-LA should use BLAS calling conventions.
+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.
-@item
-Environment variables controlling actions on arithmetic exceptions like
-overflow, underflow, precision loss -- Generate NaN, abort, default.
-action.
+In the future, the GNU Fortran compiler will also support ISO/IEC
+1539-1:2004 (Fortran 2003), ISO/IEC 1539-1:2010 (Fortran 2008) and
+future Fortran standards. Partial support of the Fortran 2003 and
+Fortran 2008 standard is already provided; the current status of the
+support is reported in the @ref{Fortran 2003 status} and
+@ref{Fortran 2008 status} sections of the documentation.
-@item
-Set precision for fp units that support it (i387).
+Additionally, the GNU Fortran compilers supports the OpenMP specification
+(version 3.0, @url{http://openmp.org/@/wp/@/openmp-specifications/}).
-@item
-Variable for setting fp rounding mode.
+@node Varying Length Character Strings
+@subsection Varying Length Character Strings
+@cindex Varying length character strings
+@cindex Varying length strings
+@cindex strings, varying length
-@item
-Variable to fill uninitialized variables with a user-defined bit
-pattern.
+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
+@uref{http://www.fortran.com/@/iso_varying_string.f95} and at
+@uref{ftp://ftp.nag.co.uk/@/sc22wg5/@/ISO_VARYING_STRING/}.
-@item
-Environment variable controlling filename that is opened for that unit
-number.
-@item
-Environment variable to clear/trash memory being freed.
-@item
-Environment variable to control tracing of allocations and frees.
+@c =====================================================================
+@c PART I: INVOCATION REFERENCE
+@c =====================================================================
-@item
-Environment variable to display allocated memory at normal program end.
+@tex
+\part{I}{Invoking GNU Fortran}
+@end tex
-@item
-Environment variable for filename for * IO-unit.
+@c ---------------------------------------------------------------------
+@c Compiler Options
+@c ---------------------------------------------------------------------
-@item
-Environment variable for temporary file directory.
+@include invoke.texi
-@item
-Environment variable forcing standard output to be line buffered (unix).
-@end itemize
+@c ---------------------------------------------------------------------
+@c Runtime
+@c ---------------------------------------------------------------------
@node Runtime
@chapter Runtime: Influencing runtime behavior with environment variables
-@cindex Runtime
+@cindex environment variable
The behavior of the @command{gfortran} can be influenced by
environment variables.
* GFORTRAN_STDERR_UNIT:: Unit number for standard error
* GFORTRAN_USE_STDERR:: Send library output to standard error
* GFORTRAN_TMPDIR:: Directory for scratch files
-* GFORTRAN_UNBUFFERED_ALL:: Don't buffer output
+* GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
+* GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
* GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
* GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
* GFORTRAN_DEFAULT_RECL:: Default record length for new files
* GFORTRAN_LIST_SEPARATOR:: Separator for list output
* GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
+* GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors
+* GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
@end menu
@node GFORTRAN_STDIN_UNIT
This environment variable controls where library output is sent.
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.
@node GFORTRAN_TMPDIR
This environment variable controls where scratch files are
created. If this environment variable is missing,
-gfortran searches for the environment variable @env{TMP}. If
-this is also missing, the default is @file{/tmp}.
+GNU Fortran searches for the environment variable @env{TMP}, then @env{TEMP}.
+If these are missing, the default is @file{/tmp}.
@node GFORTRAN_UNBUFFERED_ALL
-@section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer output
+@section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer I/O on all units
+
+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
+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.
+This is the default.
+
+@node GFORTRAN_UNBUFFERED_PRECONNECTED
+@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units
-This environment variable controls whether all output is unbuffered.
-If the first letter is @samp{y}, @samp{Y} or @samp{1}, all output is
-unbuffered. This will slow down large writes. If the first letter is
-@samp{n}, @samp{N} or @samp{0}, output is buffered. This is the
-default.
+The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
+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
+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.
@node GFORTRAN_SHOW_LOCUS
@section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors
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
@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
@section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted
a plus sign is printed
where permitted by the Fortran standard. If the first letter
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
@section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files
-This environment variable specifies the default record length for
-files which are opened without a @code{RECL} tag in the @code{OPEN}
-statement. This must be a positive integer. The default value is
-1073741824.
+This environment variable specifies the default record length, in
+bytes, for files which are opened without a @code{RECL} tag in the
+@code{OPEN} statement. This must be a positive integer. The
+default value is 1073741824 bytes (1 GB).
@node GFORTRAN_LIST_SEPARATOR
@section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output
@smallexample
$ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out
@end smallexample
-when @code{a.out} is the gfortran 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.
@node GFORTRAN_CONVERT_UNIT
to change the representation of data for unformatted files.
The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is:
@smallexample
-GFORTRAN_CONVERT_UNIT: mode | mode ';' exception ;
+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 ;
@item @code{NATIVE} Use the native format. This is the default.
@item @code{SWAP} Swap between little- and big-endian.
@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.
@end itemize
A missing mode for an exception is taken to mean @code{BIG_ENDIAN}.
-Examples of values for @code{GFORTRAN_CONVERT_UNIT} are:
+Examples of values for @env{GFORTRAN_CONVERT_UNIT} are:
@itemize @w{}
@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
@end itemize
Setting the environment variables should be done on the command
-line or via the @code{export}
-command for @code{sh}-compatible shells and via @code{setenv}
-for @code{csh}-compatible shells.
+line or via the @command{export}
+command for @command{sh}-compatible shells and via @command{setenv}
+for @command{csh}-compatible shells.
-Example for @code{sh}:
+Example for @command{sh}:
@smallexample
$ gfortran foo.f90
$ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out
@end smallexample
-Example code for @code{csh}:
+Example code for @command{csh}:
@smallexample
% gfortran foo.f90
% setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
@xref{CONVERT specifier}, for an alternative way to specify the
data representation for unformatted files. @xref{Runtime Options}, for
setting a default data representation for the whole program. The
-@code{CONVERT} specifier overrides the @code{-fconvert} compile options.
+@code{CONVERT} specifier overrides the @option{-fconvert} compile options.
-@c ---------------------------------------------------------------------
-@c Extensions
-@c ---------------------------------------------------------------------
+@emph{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.
-@c Maybe this chapter should be merged with the 'Standards' section,
-@c whenever that is written :-)
+@node GFORTRAN_ERROR_DUMPCORE
+@section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors
-@node Extensions
-@chapter Extensions
-@cindex Extension
+If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to
+@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
+dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default
+is not to core dump unless the @option{-fdump-core} compile option
+was used.
-@command{gfortran} implements a number of extensions over standard
-Fortran. This chapter contains information on their syntax and
-meaning. There are currently two categories of @command{gfortran}
-extensions, those that provide functionality beyond that provided
-by any standard, and those that are supported by @command{gfortran}
-purely for backward compatibility with legacy compilers. By default,
-@option{-std=gnu} allows the compiler to accept both types of
-extensions, but to warn about the use of the latter. Specifying
-either @option{-std=f95} or @option{-std=f2003} disables both types
-of extensions, and @option{-std=legacy} allows both without warning.
+@node GFORTRAN_ERROR_BACKTRACE
+@section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
+
+If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to
+@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
+then a backtrace is printed when a run-time error occurs.
+To disable the backtracing, set the variable to
+@samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
+unless the @option{-fbacktrace} compile option
+was used.
+
+@c =====================================================================
+@c PART II: LANGUAGE REFERENCE
+@c =====================================================================
+
+@tex
+\part{II}{Language Reference}
+@end tex
+
+@c ---------------------------------------------------------------------
+@c Fortran 2003 and 2008 Status
+@c ---------------------------------------------------------------------
+
+@node Fortran 2003 and 2008 status
+@chapter Fortran 2003 and 2008 Status
@menu
-* Old-style kind specifications::
-* Old-style variable initialization::
-* Extensions to namelist::
-* X format descriptor::
-* Commas in FORMAT specifications::
-* Missing period in FORMAT specifications::
-* I/O item lists::
-* Hexadecimal constants::
-* Real array indices::
-* Unary operators::
-* Implicitly interconvert LOGICAL and INTEGER::
-* Hollerith constants support::
-* Cray pointers::
-* CONVERT specifier::
-* OpenMP::
+* Fortran 2003 status::
+* Fortran 2008 status::
@end menu
-@node Old-style kind specifications
-@section Old-style kind specifications
-@cindex Kind specifications
+@node Fortran 2003 status
+@section Fortran 2003 status
-@command{gfortran} allows old-style kind specifications in
-declarations. These look like:
-@smallexample
- TYPESPEC*k x,y,z
-@end smallexample
-where @code{TYPESPEC} is a basic type, and where @code{k} is a valid kind
-number for that type. The statement then declares @code{x}, @code{y}
-and @code{z} to be of type @code{TYPESPEC} with kind @code{k}. In
-other words, it is equivalent to the standard conforming declaration
-@smallexample
- TYPESPEC(k) x,y,z
-@end smallexample
+GNU Fortran supports several Fortran 2003 features; an incomplete
+list can be found below. See also the
+@uref{http://gcc.gnu.org/wiki/Fortran2003, wiki page} about Fortran 2003.
-@node Old-style variable initialization
-@section Old-style variable initialization
-@cindex Initialization
+@itemize
+@item
+Intrinsics @code{command_argument_count}, @code{get_command},
+@code{get_command_argument}, @code{get_environment_variable}, and
+@code{move_alloc}.
-@command{gfortran} allows old-style initialization of variables of the
-form:
-@smallexample
- INTEGER*4 i/1/,j/2/
- REAL*8 x(2,2) /3*0.,1./
-@end smallexample
-These are only allowed in declarations without double colons
-(@code{::}), as these were introduced in Fortran 90 which also
-introduced a new syntax for variable initializations. The syntax for
-the individual initializers is as for the @code{DATA} statement, but
-unlike in a @code{DATA} statement, an initializer only applies to the
-variable immediately preceding. In other words, something like
-@code{INTEGER I,J/2,3/} is not valid.
+@item
+@cindex array, constructors
+@cindex @code{[...]}
+Array constructors using square brackets. That is, @code{[...]} rather
+than @code{(/.../)}. Type-specification for array constructors like
+@code{(/ some-type :: ... /)}.
-Examples of standard conforming code equivalent to the above example, are:
-@smallexample
-! Fortran 90
- INTEGER(4) :: i = 1, j = 2
- REAL(8) :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
-! Fortran 77
- INTEGER i, j
- DOUBLE PRECISION x(2,2)
- DATA i,j,x /1,2,3*0.,1./
-@end smallexample
+@item
+@cindex @code{FLUSH} statement
+@cindex statement, @code{FLUSH}
+@code{FLUSH} statement.
-@node Extensions to namelist
-@section Extensions to namelist
-@cindex Namelist
+@item
+@cindex @code{IOMSG=} specifier
+@code{IOMSG=} specifier for I/O statements.
-@command{gfortran} 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:
+@item
+@cindex @code{ENUM} statement
+@cindex @code{ENUMERATOR} statement
+@cindex statement, @code{ENUM}
+@cindex statement, @code{ENUMERATOR}
+@opindex @code{fshort-enums}
+Support for the declaration of enumeration constants via the
+@code{ENUM} and @code{ENUMERATOR} statements. Interoperability with
+@command{gcc} is guaranteed also for the case where the
+@command{-fshort-enums} command line option is given.
-Old-style use of $ instead of &
-@smallexample
-$MYNML
- X(:)%Y(2) = 1.0 2.0 3.0
- CH(1:4) = "abcd"
-$END
-@end smallexample
+@item
+@cindex TR 15581
+TR 15581:
+@itemize
+@item
+@cindex @code{ALLOCATABLE} dummy arguments
+@code{ALLOCATABLE} dummy arguments.
+@item
+@cindex @code{ALLOCATABLE} function results
+@code{ALLOCATABLE} function results
+@item
+@cindex @code{ALLOCATABLE} components of derived types
+@code{ALLOCATABLE} components of derived types
+@end itemize
-It should be noticed that the default terminator is / rather than &END.
+@item
+@cindex @code{ALLOCATE}
+The @code{ERRMSG=} tag is now supported in @code{ALLOCATE} and
+@code{DEALLOCATE} statements. The @code{SOURCE=} tag is supported
+in an @code{ALLOCATE} statement. An @emph{intrinsic-type-spec}
+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.
-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:
-@smallexample
-?
+@item
+@cindex @code{STREAM} I/O
+@cindex @code{ACCESS='STREAM'} I/O
+The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,
+allowing I/O without any record structure.
-&mynml
- x
- x%y
- ch
-&end
-@end smallexample
+@item
+Namelist input/output for internal files.
-Entering =? outputs the namelist to stdout, as if WRITE (*,NML = mynml)
-had been called:
-@smallexample
-=?
+@item
+@cindex @code{PROTECTED} statement
+@cindex statement, @code{PROTECTED}
+The @code{PROTECTED} statement and attribute.
-&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, /
-@end smallexample
+@item
+@cindex @code{VALUE} statement
+@cindex statement, @code{VALUE}
+The @code{VALUE} statement and attribute.
+
+@item
+@cindex @code{VOLATILE} statement
+@cindex statement, @code{VOLATILE}
+The @code{VOLATILE} statement and attribute.
+
+@item
+@cindex @code{IMPORT} statement
+@cindex statement, @code{IMPORT}
+The @code{IMPORT} statement, allowing to import
+host-associated derived types.
+
+@item
+@cindex @code{USE, INTRINSIC} statement
+@cindex statement, @code{USE, INTRINSIC}
+@cindex @code{ISO_FORTRAN_ENV} statement
+@cindex statement, @code{ISO_FORTRAN_ENV}
+@code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC}
+attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV},
+@code{OMP_LIB} and @code{OMP_LIB_KINDS}.
+
+@item
+Renaming of operators in the @code{USE} statement.
+
+@item
+@cindex ISO C Bindings
+Interoperability with C (ISO C Bindings)
+
+@item
+BOZ as argument of @code{INT}, @code{REAL}, @code{DBLE} and @code{CMPLX}.
+
+@item
+@cindex type-bound procedure
+@cindex type-bound operator
+Type-bound procedures with @code{PROCEDURE} or @code{GENERIC}, and operators
+bound to a derived-type.
+
+@item
+@cindex @code{EXTENDS}
+@cindex derived-type extension
+Extension of derived-types (the @code{EXTENDS(...)} syntax).
+
+@item
+@cindex @code{ABSTRACT} type
+@cindex @code{DEFERRED} procedure binding
+@code{ABSTRACT} derived-types and declaring procedure bindings @code{DEFERRED}.
+
+@end itemize
+
+
+@node Fortran 2008 status
+@section 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
+@url{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
+@uref{http://www.nag.co.uk/sc22wg5/, WG5}.
+
+The GNU Fortran supports several of the new features of Fortran 2008; the
+@uref{http://gcc.gnu.org/wiki/Fortran2008Status, wiki} has some information
+about the current Fortran 2008 implementation status. In particular, the
+following is implemented.
+
+@itemize
+@item The @option{-std=f2008} option and support for the file extensions
+@file{.f08} and @file{.F08}.
+
+@item The @code{OPEN} statement now supports the @code{NEWUNIT=} option,
+which returns a unique file unit, thus preventing inadvertent use of the
+same unit in different parts of the program.
+
+@item The @code{g0} format descriptor and unlimited format items.
+
+@item The mathematical intrinsics @code{ASINH}, @code{ACOSH}, @code{ATANH},
+@code{ERF}, @code{ERFC}, @code{GAMMA}, @code{LOG_GAMMA}, @code{BESSEL_J0},
+@code{BESSEL_J1}, @code{BESSEL_JN}, @code{BESSEL_Y0}, @code{BESSEL_Y1},
+@code{BESSEL_YN}, @code{HYPOT}, @code{NORM2}, and @code{ERFC_SCALED}.
+
+@item Using complex arguments with @code{TAN}, @code{SINH}, @code{COSH},
+@code{TANH}, @code{ASIN}, @code{ACOS}, and @code{ATAN} is now possible;
+@code{ATAN}(@var{Y},@var{X}) is now an alias for @code{ATAN2}(@var{Y},@var{X}).
+
+@item Support of the @code{PARITY} intrinsic functions.
+
+@item The following bit intrinsics: @code{LEADZ} and @code{TRAILZ} for
+counting the number of leading and trailing zero bits, @code{POPCNT} and
+@code{POPPAR} for counting the number of one bits and returning the parity;
+@code{BGE}, @code{BGT}, @code{BLE}, and @code{BLT} for bitwise comparisons;
+@code{DSHIFTL} and @code{DSHIFTR} for combined left and right shifts,
+@code{MASKL} and @code{MASKR} for simple left and right justified masks,
+@code{MERGE_BITS} for a bitwise merge using a mask, @code{SHIFTA},
+@code{SHIFTL} and @code{SHIFTR} for shift operations, and the
+transformational bit intrinsics @code{IALL}, @code{IANY} and @code{IPARITY}.
+
+@item Support of the @code{EXECUTE_COMMAND_LINE} intrinsic subroutine.
+
+@item Support for the @code{STORAGE_SIZE} intrinsic inquiry function.
+
+@item The @code{INT@{8,16,32@}} and @code{REAL@{32,64,128@}} kind type
+parameters and the array-valued named constants @code{INTEGER_KINDS},
+@code{LOGICAL_KINDS}, @code{REAL_KINDS} and @code{CHARACTER_KINDS} of
+the intrinsic module @code{ISO_FORTRAN_ENV}.
+
+@item The module procedures @code{C_SIZEOF} of the intrinsic module
+@code{ISO_C_BINDINGS} and @code{COMPILER_VERSION} and @code{COMPILER_OPTIONS}
+of @code{ISO_FORTRAN_ENV}.
+
+@item Experimental coarray support (for one image only), use the
+@option{-fcoarray=single} flag to enable it.
+
+@item The @code{BLOCK} construct is supported.
+
+@item The @code{STOP} and the new @code{ERROR STOP} statements now
+support all constant expressions.
+
+@item Support for the @code{CONTIGUOUS} attribute.
+
+@item Support for @code{ALLOCATE} with @code{MOLD}.
+
+@item Support for the @code{IMPURE} attribute for procedures, which
+allows for @code{ELEMENTAL} procedures without the restrictions of
+@code{PURE}.
+
+@item Null pointers (including @code{NULL()}) and not-allocated variables
+can be used as actual argument to optional non-pointer, non-allocatable
+dummy arguments, denoting an absent argument.
+
+@item Non-pointer variables with @code{TARGET} attribute can be used as
+actual argument to @code{POINTER} dummies with @code{INTENT(IN)}.
+
+@item Pointers including procedure pointers and those in a derived
+type (pointer components) can now be initialized by a target instead
+of only by @code{NULL}.
+
+@item The @code{EXIT} statement (with construct-name) can be now be
+used to leave not only the @code{DO} but also the @code{ASSOCIATE},
+@code{BLOCK}, @code{IF}, @code{SELECT CASE} and @code{SELECT TYPE}
+constructs.
+
+@item Internal procedures can now be used as actual argument.
+
+@item Minor features: obsolesce diagnostics for @code{ENTRY} with
+@option{-std=f2008}; a line may start with a semicolon; for internal
+and module procedures @code{END} can be used instead of
+@code{END SUBROUTINE} and @code{END FUNCTION}; @code{SELECTED_REAL_KIND}
+now also takes a @code{RADIX} argument; intrinsic types are supported
+for @code{TYPE}(@var{intrinsic-type-spec}); multiple type-bound procedures
+can be declared in a single @code{PROCEDURE} statement; implied-shape
+arrays are supported for named constants (@code{PARAMETER}).
+@end itemize
+
+
+
+@c ---------------------------------------------------------------------
+@c Compiler Characteristics
+@c ---------------------------------------------------------------------
+
+@node Compiler Characteristics
+@chapter 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.
+
+@menu
+* KIND Type Parameters::
+* Internal representation of LOGICAL variables::
+@end menu
+
+
+@node KIND Type Parameters
+@section KIND Type Parameters
+@cindex kind
+
+The @code{KIND} type parameters supported by GNU Fortran for the primitive
+data types are:
+
+@table @code
+
+@item INTEGER
+1, 2, 4, 8*, 16*, default: 4 (1)
+
+@item LOGICAL
+1, 2, 4, 8*, 16*, default: 4 (1)
+
+@item REAL
+4, 8, 10**, 16**, default: 4 (2)
+
+@item COMPLEX
+4, 8, 10**, 16**, default: 4 (2)
+
+@item CHARACTER
+1, 4, default: 1
+
+@end table
+
+@noindent
+* = not available on all systems @*
+** = not available on all systems; additionally 10 and 16 are never
+available at the same time @*
+(1) Unless -fdefault-integer-8 is used @*
+(2) Unless -fdefault-real-8 is used
+
+@noindent
+The @code{KIND} value matches the storage size in bytes, except for
+@code{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 @code{SELECT_*_KIND} intrinsics instead of the concrete values.
+
+
+@node Internal representation of LOGICAL variables
+@section Internal representation of LOGICAL variables
+@cindex logical, variable representation
+
+The Fortran standard does not specify how variables of @code{LOGICAL}
+type are represented, beyond requiring that @code{LOGICAL} variables
+of default kind have the same storage size as default @code{INTEGER}
+and @code{REAL} variables. The GNU Fortran internal representation is
+as follows.
+
+A @code{LOGICAL(KIND=N)} variable is represented as an
+@code{INTEGER(KIND=N)} variable, however, with only two permissible
+values: @code{1} for @code{.TRUE.} and @code{0} for
+@code{.FALSE.}. Any other integer value results in undefined behavior.
+
+Note that for mixed-language programming using the
+@code{ISO_C_BINDING} feature, there is a @code{C_BOOL} kind that can
+be used to create @code{LOGICAL(KIND=C_BOOL)} variables which are
+interoperable with the C99 _Bool type. The C99 _Bool type has an
+internal representation described in the C99 standard, which is
+identical to the above description, i.e. with 1 for true and 0 for
+false being the only permissible values. Thus the internal
+representation of @code{LOGICAL} variables in GNU Fortran is identical
+to C99 _Bool, except for a possible difference in storage size
+depending on the kind.
+
+@c ---------------------------------------------------------------------
+@c Extensions
+@c ---------------------------------------------------------------------
+
+@c Maybe this chapter should be merged with the 'Standards' section,
+@c whenever that is written :-)
+
+@node Extensions
+@chapter Extensions
+@cindex 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.
+
+@menu
+* Extensions implemented in GNU Fortran::
+* Extensions not implemented in GNU Fortran::
+@end menu
+
+
+@node Extensions implemented in GNU Fortran
+@section Extensions implemented in GNU Fortran
+@cindex extensions, implemented
+
+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,
+@option{-std=gnu} allows the compiler to accept both types of
+extensions, but to warn about the use of the latter. Specifying
+either @option{-std=f95}, @option{-std=f2003} or @option{-std=f2008}
+disables both types of extensions, and @option{-std=legacy} allows both
+without warning.
+
+@menu
+* Old-style kind specifications::
+* Old-style variable initialization::
+* Extensions to namelist::
+* X format descriptor without count field::
+* Commas in FORMAT specifications::
+* Missing period in FORMAT specifications::
+* I/O item lists::
+* BOZ literal constants::
+* Real array indices::
+* Unary operators::
+* Implicitly convert LOGICAL and INTEGER values::
+* Hollerith constants support::
+* Cray pointers::
+* CONVERT specifier::
+* OpenMP::
+* Argument list functions::
+@end menu
+
+@node Old-style kind specifications
+@subsection Old-style kind specifications
+@cindex kind, old-style
+
+GNU Fortran allows old-style kind specifications in declarations. These
+look like:
+@smallexample
+ TYPESPEC*size x,y,z
+@end smallexample
+@noindent
+where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL},
+etc.), and where @code{size} is a byte count corresponding to the
+storage size of a valid kind for that type. (For @code{COMPLEX}
+variables, @code{size} is the total size of the real and imaginary
+parts.) The statement then declares @code{x}, @code{y} and @code{z} to
+be of type @code{TYPESPEC} with the appropriate kind. This is
+equivalent to the standard-conforming declaration
+@smallexample
+ TYPESPEC(k) x,y,z
+@end smallexample
+@noindent
+where @code{k} is the kind parameter suitable for the intended precision. As
+kind parameters are implementation-dependent, use the @code{KIND},
+@code{SELECTED_INT_KIND} and @code{SELECTED_REAL_KIND} intrinsics to retrieve
+the correct value, for instance @code{REAL*8 x} can be replaced by:
+@smallexample
+INTEGER, PARAMETER :: dbl = KIND(1.0d0)
+REAL(KIND=dbl) :: x
+@end smallexample
+
+@node Old-style variable initialization
+@subsection Old-style variable initialization
+
+GNU Fortran allows old-style initialization of variables of the
+form:
+@smallexample
+ INTEGER i/1/,j/2/
+ REAL x(2,2) /3*0.,1./
+@end smallexample
+The syntax for the initializers is as for the @code{DATA} statement, but
+unlike in a @code{DATA} statement, an initializer only applies to the
+variable immediately preceding the initialization. In other words,
+something like @code{INTEGER I,J/2,3/} is not valid. This style of
+initialization is only allowed in declarations without double colons
+(@code{::}); 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:
+@smallexample
+! 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./
+@end smallexample
+
+Note that variables which are explicitly initialized in declarations
+or in @code{DATA} statements automatically acquire the @code{SAVE}
+attribute.
+
+@node Extensions to namelist
+@subsection Extensions to namelist
+@cindex 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 @samp{$} instead of @samp{&}
+@smallexample
+$MYNML
+ X(:)%Y(2) = 1.0 2.0 3.0
+ CH(1:4) = "abcd"
+$END
+@end smallexample
+
+It should be noted that the default terminator is @samp{/} rather than
+@samp{&END}.
+
+Querying of the namelist when inputting from stdin. After at least
+one space, entering @samp{?} sends to stdout the namelist name and the names of
+the variables in the namelist:
+@smallexample
+ ?
+
+&mynml
+ x
+ x%y
+ ch
+&end
+@end smallexample
+
+Entering @samp{=?} outputs the namelist to stdout, as if
+@code{WRITE(*,NML = mynml)} had been called:
+@smallexample
+=?
+
+&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, /
+@end smallexample
To aid this dialog, when input is from stdin, errors send their
-messages to stderr and execution continues, even if IOSTAT is set.
+messages to stderr and execution continues, even if @code{IOSTAT} is set.
-PRINT namelist is permitted. This causes an error if -std=f95 is used.
+@code{PRINT} namelist is permitted. This causes an error if
+@option{-std=f95} is used.
@smallexample
PROGRAM test_print
REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/)
END PROGRAM test_print
@end smallexample
-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 succeeding elements will be 1.00 and 2.00.
+Expanded namelist reads are permitted. This causes an error if
+@option{-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.
@smallexample
&MYNML
X(1,1) = 0.00 , 1.00 , 2.00
/
@end smallexample
-@node X format descriptor
-@section X format descriptor
-@cindex X format descriptor
+@node X format descriptor without count field
+@subsection @code{X} format descriptor without count field
-To support legacy codes, @command{gfortran} 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.
+To support legacy codes, GNU Fortran permits the count field of the
+@code{X} edit descriptor in @code{FORMAT} statements to be omitted.
+When omitted, the count is implicitly assumed to be one.
@smallexample
PRINT 10, 2, 3
@end smallexample
@node Commas in FORMAT specifications
-@section Commas in FORMAT specifications
-@cindex Commas in FORMAT specifications
+@subsection Commas in @code{FORMAT} specifications
-To support legacy codes, @command{gfortran} allows the comma separator
+To support legacy codes, GNU Fortran allows the comma separator
to be omitted immediately before and after character string edit
-descriptors in FORMAT statements.
+descriptors in @code{FORMAT} statements.
@smallexample
PRINT 10, 2, 3
@node Missing period in FORMAT specifications
-@section Missing period in FORMAT specifications
-@cindex Missing period in FORMAT specifications
+@subsection Missing period in @code{FORMAT} specifications
-To support legacy codes, @command{gfortran} 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.
+To support legacy codes, GNU Fortran allows missing periods in format
+specifications if and only if @option{-std=legacy} is given on the
+command line. This is considered non-conforming code and is
+discouraged.
@smallexample
REAL :: value
@end smallexample
@node I/O item lists
-@section I/O item lists
+@subsection I/O item lists
@cindex I/O item lists
-To support legacy codes, @command{gfortran} 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.
-
-@node Hexadecimal constants
-@section Hexadecimal constants
-@cindex Hexadecimal constants
-
-As a GNU extension, @command{gfortran} allows hexadecimal constants to
-be specified using the X prefix, in addition to the standard Z prefix.
+To support legacy codes, GNU Fortran allows the input item list
+of the @code{READ} statement, and the output item lists of the
+@code{WRITE} and @code{PRINT} statements, to start with a comma.
+
+@node BOZ literal constants
+@subsection BOZ literal constants
+@cindex BOZ literal constants
+
+Besides decimal constants, Fortran also supports binary (@code{b}),
+octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
+syntax is: @samp{prefix quote digits quote}, were the prefix is
+either @code{b}, @code{o} or @code{z}, quote is either @code{'} or
+@code{"} and the digits are for binary @code{0} or @code{1}, for
+octal between @code{0} and @code{7}, and for hexadecimal between
+@code{0} and @code{F}. (Example: @code{b'01011101'}.)
+
+Up to Fortran 95, BOZ literals were only allowed to initialize
+integer variables in DATA statements. Since Fortran 2003 BOZ literals
+are also allowed as argument of @code{REAL}, @code{DBLE}, @code{INT}
+and @code{CMPLX}; the result is the same as if the integer BOZ
+literal had been converted by @code{TRANSFER} to, respectively,
+@code{real}, @code{double precision}, @code{integer} or @code{complex}.
+As GNU Fortran extension the intrinsic procedures @code{FLOAT},
+@code{DFLOAT}, @code{COMPLEX} and @code{DCMPLX} are treated alike.
+
+As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
+be specified using the @code{X} prefix, in addition to the standard
+@code{Z} prefix. The BOZ literal can also be specified by adding a
+suffix to the string, for example, @code{Z'ABC'} and @code{'ABC'Z} are
+equivalent.
+
+Furthermore, GNU Fortran allows using BOZ literal constants outside
+DATA statements and the four intrinsic functions allowed by Fortran 2003.
+In DATA statements, in direct assignments, where the right-hand side
+only contains a BOZ literal constant, and for old-style initializers of
+the form @code{integer i /o'0173'/}, the constant is transferred
+as if @code{TRANSFER} had been used; for @code{COMPLEX} numbers, only
+the real part is initialized unless @code{CMPLX} is used. In all other
+cases, the BOZ literal constant is converted to an @code{INTEGER} value with
+the largest decimal representation. This value is then converted
+numerically to the type and kind of the variable in question.
+(For instance, @code{real :: r = b'0000001' + 1} initializes @code{r}
+with @code{2.0}.) As different compilers implement the extension
+differently, one should be careful when doing bitwise initialization
+of non-integer variables.
+
+Note that initializing an @code{INTEGER} variable with a statement such
+as @code{DATA i/Z'FFFFFFFF'/} will give an integer overflow error rather
+than the desired result of @math{-1} when @code{i} is a 32-bit integer
+on a system that supports 64-bit integers. The @samp{-fno-range-check}
+option can be used as a workaround for legacy code that initializes
+integers in this manner.
@node Real array indices
-@section Real array indices
-@cindex Real array indices
+@subsection Real array indices
+@cindex array, indices of type real
-As a GNU extension, @command{gfortran} allows arrays to be indexed using
-real types, whose values are implicitly converted to integers.
+As an extension, GNU Fortran allows the use of @code{REAL} expressions
+or variables as array indices.
@node Unary operators
-@section Unary operators
-@cindex Unary operators
+@subsection Unary operators
+@cindex operators, unary
-As a GNU extension, @command{gfortran} allows unary plus and unary
-minus operators to appear as the second operand of binary arithmetic
-operators without the need for parenthesis.
+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.
@smallexample
X = Y * -Z
@end smallexample
-@node Implicitly interconvert LOGICAL and INTEGER
-@section Implicitly interconvert LOGICAL and INTEGER
-@cindex Implicitly interconvert LOGICAL and INTEGER
-
-As a GNU extension for backwards compatibility with other compilers,
-@command{gfortran} allows the implicit conversion of LOGICALs to INTEGERs
-and vice versa. When converting from a LOGICAL to an INTEGER, the numeric
-value of @code{.FALSE.} is zero, and that of @code{.TRUE.} is one. When
-converting from INTEGER to LOGICAL, the value zero is interpreted as
+@node Implicitly convert LOGICAL and INTEGER values
+@subsection Implicitly convert @code{LOGICAL} and @code{INTEGER} values
+@cindex conversion, to integer
+@cindex conversion, to logical
+
+As an extension for backwards compatibility with other compilers, GNU
+Fortran allows the implicit conversion of @code{LOGICAL} values to
+@code{INTEGER} values and vice versa. When converting from a
+@code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as
+zero, and @code{.TRUE.} is interpreted as one. When converting from
+@code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as
@code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}.
@smallexample
- INTEGER*4 i
- i = .FALSE.
+ LOGICAL :: l
+ l = 1
+@end smallexample
+@smallexample
+ INTEGER :: i
+ i = .TRUE.
@end smallexample
+However, there is no implicit conversion of @code{INTEGER} values in
+@code{if}-statements, nor of @code{LOGICAL} or @code{INTEGER} values
+in I/O operations.
+
@node Hollerith constants support
-@section Hollerith constants support
+@subsection Hollerith constants support
@cindex Hollerith constants
-A Hollerith constant is a string of characters preceded by the letter @samp{H}
-or @samp{h}, and there must be an literal, unsigned, nonzero default integer
-constant indicating the number of characters in the string. Hollerith constants
-are stored as byte strings, one character per byte.
-
-@command{gfortran} supports Hollerith constants. They can be used as the right
-hands in the @code{DATA} statement and @code{ASSIGN} statement, also as the
-arguments. The left hands can be of Integer, Real, Complex and Logical type.
-The constant will be padded or truncated to fit the size of left hand.
+GNU Fortran supports Hollerith constants in assignments, function
+arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith
+constant is written as a string of characters preceded by an integer
+constant indicating the character count, and the letter @code{H} or
+@code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER},
+@code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The
+constant will be padded or truncated to fit the size of the variable in
+which it is stored.
-Valid Hollerith constants examples:
+Examples of valid uses of Hollerith constants:
@smallexample
-complex*16 x(2)
-data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
-call foo (4H abc)
-x(1) = 16Habcdefghijklmnop
+ complex*16 x(2)
+ data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
+ x(1) = 16HABCDEFGHIJKLMNOP
+ call foo (4h abc)
@end smallexample
Invalid Hollerith constants examples:
@smallexample
-integer*4 a
-a = 8H12345678 ! The Hollerith constant is too long. It will be truncated.
-a = 0H ! At least one character needed.
+ integer*4 a
+ a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
+ a = 0H ! At least one character is needed.
@end smallexample
+In general, Hollerith constants were used to provide a rudimentary
+facility for handling character strings in early Fortran compilers,
+prior to the introduction of @code{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 @code{TRANSFER} statement, as in this example.
+@smallexample
+ INTEGER(KIND=4) :: a
+ a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd
+@end smallexample
+
+
@node Cray pointers
-@section Cray pointers
-@cindex Cray pointers
+@subsection Cray pointers
+@cindex pointer, Cray
Cray pointers are part of a non-standard extension that provides a
C-like pointer in Fortran. This is accomplished through a pair of
@end smallexample
The pointer is an integer that is intended to hold a memory address.
The pointee may be an array or scalar. 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 -- but a pointee cannot be an assumed
-shape array. No space is allocated for the pointee.
+size array---that is, the last dimension may be left unspecified by
+using a @code{*} in place of a value---but 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
ipt = loc (target)
ipt = ipt + 1
@end smallexample
-The last statement does not set ipt to the address of
-@code{target(1)}, as one familiar with C pointer arithmetic might
-expect. Adding 1 to ipt just adds one byte to the address stored in
-ipt.
+The last statement does not set @code{ipt} to the address of
+@code{target(1)}, as it would in C pointer arithmetic. Adding @code{1}
+to @code{ipt} just adds one byte to the address stored in @code{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(), loc() is essentially the C '&' operator, except the
-address is cast to an integer type:
+function @code{LOC()}. The @code{LOC()} function is equivalent to the
+@code{&} operator in C, except the address is cast to an integer type:
@smallexample
real ar(10)
pointer(ipt, arpte(10))
ipt = loc(ar) ! Makes arpte is an alias for ar
arpte(1) = 1.0 ! Sets ar(1) to 1.0
@end smallexample
-The pointer can also be set by a call to a malloc-type
-function. There is no malloc intrinsic implemented as part of the
-Cray pointer extension, but it might be a useful future addition to
-@command{gfortran}. Even without an intrinsic malloc function,
-dynamic memory allocation can be combined with Cray pointers by
-calling a short C function:
-@smallexample
-mymalloc.c:
-
- void mymalloc_(void **ptr, int *nbytes)
- @{
- *ptr = malloc(*nbytes);
- return;
- @}
-
-caller.f:
-
- program caller
- integer ipinfo;
- real*4 data
- pointer (ipdata, data(1024))
- call mymalloc(ipdata,4*1024)
- end
-@end smallexample
+The pointer can also be set by a call to the @code{MALLOC} intrinsic
+(see @ref{MALLOC}).
+
Cray pointees often are used to alias an existing variable. For
example:
@smallexample
pointer (ipt, iarr)
ipt = loc(target)
@end smallexample
-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're 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 gfortran; 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
-attributes ALLOCATABLE, INTENT, OPTIONAL, DUMMY, TARGET, EXTERNAL,
-INTRINSIC, or POINTER. Pointers may not have the attributes
-DIMENSION, POINTER, TARGET, ALLOCATABLE, EXTERNAL, or INTRINSIC.
-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.
+As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for
+@code{target}. The optimizer, however, will not detect this aliasing, so
+it is unsafe to use @code{iarr} and @code{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
+@code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY},
+@code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers
+may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET},
+@code{ALLOCATABLE}, @code{EXTERNAL}, or @code{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:
+@smallexample
+ implicit none
+ external sub
+ pointer (subptr,subpte)
+ external subpte
+ subptr = loc(sub)
+ call subpte()
+ [...]
+ subroutine sub
+ [...]
+ end subroutine sub
+@end smallexample
A pointer may be modified during the course of a program, and this
will change the location to which the pointee refers. However, when
will not change the base address of the array that was passed.
@node CONVERT specifier
-@section CONVERT specifier
-@cindex CONVERT specifier
+@subsection @code{CONVERT} specifier
+@cindex @code{CONVERT} specifier
-gfortran allows the conversion of unformatted data between little-
+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 @code{CONVERT} specifier on the @code{OPEN} statement.
@item @code{CONVERT='NATIVE'} Use the native format. This is the default.
@item @code{CONVERT='SWAP'} Swap between little- and big-endian.
@item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation
- for unformatted files.
+for unformatted files.
@item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for
- unformatted files.
+unformatted files.
@end itemize
Using the option could look like this:
@code{INTEGER} values of all supported kinds and for @code{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 gfortran
-supports as @code{REAL(KIND=10)} will probably not work.
+m68k and x86_64, which GNU Fortran
+supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will
+probably not work.
@emph{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
-a user who does not have the source code of his program available.
+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
portable.
@node OpenMP
-@section OpenMP
+@subsection OpenMP
@cindex OpenMP
-gfortran attempts to be OpenMP Application Program Interface v2.5
-compatible when invoked with the @code{-fopenmp} option. gfortran
-then generates parallellized code according to the OpenMP directives
-used in the source. The OpenMP Fortran runtime library
-routines are provided both in a form of Fortran 90 module named
-@code{omp_lib} and in a form of a Fortran @code{include} file named
-@code{omp_lib.h}.
+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
+@uref{http://www.openmp.org/mp-documents/spec30.pdf,
+OpenMP Application Program Interface v3.0}.
+
+To enable the processing of the OpenMP directive @code{!$omp} in
+free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp}
+directives in fixed form; the @code{!$} conditional compilation sentinels
+in free form; and the @code{c$}, @code{*$} and @code{!$} sentinels
+in fixed form, @command{gfortran} needs to be invoked with the
+@option{-fopenmp}. This also arranges for automatic linking of the
+GNU OpenMP runtime library @ref{Top,,libgomp,libgomp,GNU OpenMP
+runtime library}.
+
+The OpenMP Fortran runtime library routines are provided both in a
+form of a Fortran 90 module named @code{omp_lib} and in a form of
+a Fortran @code{include} file named @file{omp_lib.h}.
+
+An example of a parallelized loop taken from Appendix A.1 of
+the OpenMP Application Program Interface v2.5:
+@smallexample
+SUBROUTINE A1(N, A, B)
+ INTEGER I, N
+ REAL B(N), A(N)
+!$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
+@end smallexample
+
+Please note:
+@itemize
+@item
+@option{-fopenmp} implies @option{-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.
+
+@item
+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
+@command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added
+to the command line. However, this is not supported by @command{gcc} and
+thus not recommended.
+@end itemize
+
+@node Argument list functions
+@subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC}
+@cindex argument list functions
+@cindex @code{%VAL}
+@cindex @code{%REF}
+@cindex @code{%LOC}
+
+GNU Fortran supports argument list functions @code{%VAL}, @code{%REF}
+and @code{%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.
+
+@code{%VAL} passes a scalar argument by value, @code{%REF} passes it by
+reference and @code{%LOC} passes its memory location. Since gfortran
+already passes scalar arguments by reference, @code{%REF} is in effect
+a do-nothing. @code{%LOC} has the same effect as a Fortran pointer.
+
+An example of passing an argument by value to a C subroutine foo.:
+@smallexample
+C
+C prototype void foo_ (float x);
+C
+ external foo
+ real*4 x
+ x = 3.14159
+ call foo (%VAL (x))
+ end
+@end smallexample
+
+For details refer to the g77 manual
+@uref{http://gcc.gnu.org/@/onlinedocs/@/gcc-3.4.6/@/g77/@/index.html#Top}.
+
+Also, @code{c_by_val.f} and its partner @code{c_by_val.c} of the
+GNU Fortran testsuite are worth a look.
+
+
+@node Extensions not implemented in GNU Fortran
+@section Extensions not implemented in GNU Fortran
+@cindex extensions, not implemented
+
+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.
+
+@c More can be found here:
+@c -- http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html
+@c -- the list of Fortran and libgfortran bugs closed as WONTFIX:
+@c http://tinyurl.com/2u4h5y
+
+@menu
+* STRUCTURE and RECORD::
+@c * UNION and MAP::
+* ENCODE and DECODE statements::
+* Variable FORMAT expressions::
+@c * Q edit descriptor::
+@c * AUTOMATIC statement::
+@c * TYPE and ACCEPT I/O Statements::
+@c * .XOR. operator::
+@c * CARRIAGECONTROL, DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers::
+@c * Omitted arguments in procedure call::
+* Alternate complex function syntax::
+@end menu
+
+
+@node STRUCTURE and RECORD
+@subsection @code{STRUCTURE} and @code{RECORD}
+@cindex @code{STRUCTURE}
+@cindex @code{RECORD}
+
+Structures are user-defined aggregate data types; this functionality was
+standardized in Fortran 90 with an different syntax, under the name of
+``derived types''. Here is an example of code using the non portable
+structure syntax:
+
+@example
+! 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)
+@end example
+
+@noindent
+This code can easily be rewritten in the Fortran 90 syntax as following:
+
+@example
+! ``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 don't change
+store_catalog(12) = pear
+print *, store_catalog(12)
+@end example
+
+
+@c @node UNION and MAP
+@c @subsection @code{UNION} and @code{MAP}
+@c @cindex @code{UNION}
+@c @cindex @code{MAP}
+@c
+@c For help writing this one, see
+@c http://www.eng.umd.edu/~nsw/ench250/fortran1.htm#UNION and
+@c http://www.tacc.utexas.edu/services/userguides/pgi/pgiws_ug/pgi32u06.htm
+
+
+@node ENCODE and DECODE statements
+@subsection @code{ENCODE} and @code{DECODE} statements
+@cindex @code{ENCODE}
+@cindex @code{DECODE}
+
+GNU Fortran doesn't support the @code{ENCODE} and @code{DECODE}
+statements. These statements are best replaced by @code{READ} and
+@code{WRITE} statements involving internal files (@code{CHARACTER}
+variables and arrays), which have been part of the Fortran standard since
+Fortran 77. For example, replace a code fragment like
+
+@smallexample
+ 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))
+@end smallexample
+
+@noindent
+with the following:
+
+@smallexample
+ 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))
+@end smallexample
+
+Similarly, replace a code fragment like
+
+@smallexample
+ 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))
+@end smallexample
+
+@noindent
+with the following:
+
+@smallexample
+ 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))
+@end smallexample
+
+
+@node Variable FORMAT expressions
+@subsection Variable @code{FORMAT} expressions
+@cindex @code{FORMAT}
+
+A variable @code{FORMAT} expression is format statement which includes
+angle brackets enclosing a Fortran expression: @code{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:
+
+@smallexample
+ WRITE(6,20) INT1
+ 20 FORMAT(I<N+1>)
+@end smallexample
+
+@noindent
+with the following:
+
+@smallexample
+c Variable declaration
+ CHARACTER(LEN=20) FMT
+c
+c Other code here...
+c
+ WRITE(FMT,'("(I", I0, ")")') N+1
+ WRITE(6,FMT) INT1
+@end smallexample
+
+@noindent
+or with:
+
+@smallexample
+c Variable declaration
+ CHARACTER(LEN=20) FMT
+c
+c Other code here...
+c
+ WRITE(FMT,*) N+1
+ WRITE(6,"(I" // ADJUSTL(FMT) // ")") INT1
+@end smallexample
+
+
+@node Alternate complex function syntax
+@subsection Alternate complex function syntax
+@cindex Complex function
+
+Some Fortran compilers, including @command{g77}, let the user declare
+complex functions with the syntax @code{COMPLEX FUNCTION name*16()}, as
+well as @code{COMPLEX*16 FUNCTION name()}. Both are non-standard, legacy
+extensions. @command{gfortran} accepts the latter form, which is more
+common, but not the former.
+
-For details refer to the actual
-@uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
-OpenMP Application Program Interface v2.5} specification.
@c ---------------------------------------------------------------------
-@include intrinsic.texi
+@c Mixed-Language Programming
+@c ---------------------------------------------------------------------
+
+@node Mixed-Language Programming
+@chapter Mixed-Language Programming
+@cindex Interoperability
+@cindex Mixed-language programming
+
+@menu
+* Interoperability with C::
+* GNU Fortran Compiler Directives::
+* Non-Fortran Main Program::
+@end menu
+
+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.
+
+
+@node Interoperability with C
+@section Interoperability with C
+
+@menu
+* Intrinsic Types::
+* Derived Types and struct::
+* Interoperable Global Variables::
+* Interoperable Subroutines and Functions::
+* Working with Pointers::
+* Further Interoperability of Fortran with C::
+@end menu
+
+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 @code{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 @code{A(n,m)} in Fortran matches
+@code{A[m][n]} in C and accessing the element @code{A(i,j)} matches
+@code{A[j-1][i-1]}. The element following @code{A(i,j)} (C: @code{A[j-1][i-1]};
+assuming @math{i < n}) in memory is @code{A(i+1,j)} (C: @code{A[j-1][i]}).
+
+@node Intrinsic Types
+@subsection 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
+@code{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 @ref{ISO_C_BINDING}.
+
+@node Derived Types and struct
+@subsection Derived Types and struct
+
+For compatibility of derived types with @code{struct}, one needs to use
+the @code{BIND(C)} attribute in the type declaration. For instance, the
+following type declaration
+
+@smallexample
+ 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
+@end smallexample
+
+matches the following @code{struct} declaration in C
+
+@smallexample
+ struct @{
+ int i1, i2;
+ /* Note: "char" might be signed or unsigned. */
+ signed char i3;
+ double d1;
+ float _Complex c1;
+ char str[5];
+ @} myType;
+@end smallexample
+
+Derived types with the C binding attribute shall not have the @code{sequence}
+attribute, type parameters, the @code{extends} attribute, nor type-bound
+procedures. Every component must be of interoperable type and kind and may not
+have the @code{pointer} or @code{allocatable} attribute. The names of the
+variables 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.
+
+@node Interoperable Global Variables
+@subsection 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 @code{MODULE},
+be of interoperable type, and have neither the @code{pointer} nor
+the @code{allocatable} attribute.
+
+@smallexample
+ 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
+@end smallexample
+
+Here, @code{_MyProject_flags} is the case-sensitive name of the variable
+as seen from C programs while @code{global_flag} is the case-insensitive
+name as seen from Fortran. If no binding name is specified, as for
+@var{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 @var{errno} of the C library as the C standard allows it to be
+a macro. Use the @code{IERRNO} intrinsic (GNU extension) instead.
+
+@node Interoperable Subroutines and Functions
+@subsection Interoperable Subroutines and Functions
+
+Subroutines and functions have to have the @code{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 only explicit size and assumed-size arrays are
+supported but not assumed-shape or allocatable arrays.
+
+To pass a variable by value, use the @code{VALUE} attribute.
+Thus the following C prototype
+
+@smallexample
+@code{int func(int i, int *j)}
+@end smallexample
+
+matches the Fortran declaration
+
+@smallexample
+ integer(c_int) function func(i,j)
+ use iso_c_binding, only: c_int
+ integer(c_int), VALUE :: i
+ integer(c_int) :: j
+@end smallexample
+
+Note that pointer arguments also frequently need the @code{VALUE} attribute,
+see @ref{Working with Pointers}.
+
+Strings are handled quite differently in C and Fortran. In C a string
+is a @code{NUL}-terminated array of characters while in Fortran each string
+has a length associated with it and is thus not terminated (by e.g.
+@code{NUL}). For example, if one wants to use the following C function,
+
+@smallexample
+ #include <stdio.h>
+ void print_C(char *string) /* equivalent: char string[] */
+ @{
+ printf("%s\n", string);
+ @}
+@end smallexample
+
+to print ``Hello World'' from Fortran, one can call it using
+
+@smallexample
+ 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)
+@end smallexample
+
+As the example shows, one needs to ensure that the
+string is @code{NUL} terminated. Additionally, the dummy argument
+@var{string} of @code{print_C} is a length-one assumed-size
+array; using @code{character(len=*)} is not allowed. The example
+above uses @code{c_char_"Hello World"} to ensure the string
+literal has the right type; typically the default character
+kind and @code{c_char} are the same and thus @code{"Hello World"}
+is equivalent. However, the standard does not guarantee this.
+
+The use of strings is now further illustrated using the C library
+function @code{strncpy}, whose prototype is
+
+@smallexample
+ char *strncpy(char *restrict s1, const char *restrict s2, size_t n);
+@end smallexample
+
+The function @code{strncpy} copies at most @var{n} characters from
+string @var{s2} to @var{s1} and returns @var{s1}. In the following
+example, we ignore the return value:
+
+@smallexample
+ 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
+@end smallexample
+
+The intrinsic procedures are described in @ref{Intrinsic Procedures}.
+
+@node Working with Pointers
+@subsection Working with Pointers
+
+C pointers are represented in Fortran via the special opaque derived type
+@code{type(c_ptr)} (with private components). Thus one needs to
+use intrinsic conversion procedures to convert from or to C pointers.
+For example,
+
+@smallexample
+ 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])
+@end smallexample
+
+When converting C to Fortran arrays, the one-dimensional @code{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 @code{VALUE} attribute. @code{void*}
+matches @code{TYPE(C_PTR), VALUE}, while @code{TYPE(C_PTR)} alone
+matches @code{void**}.
+
+Procedure pointers are handled analogously to pointers; the C type is
+@code{TYPE(C_FUNPTR)} and the intrinsic conversion procedures are
+@code{C_F_PROCPOINTER} and @code{C_FUNLOC}.
+
+Let's 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:
+
+@smallexample
+/* 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);
+@}
+@end smallexample
+
+A matching implementation for @code{get_values} in Fortran, that correctly
+receives the procedure pointer from C and is able to call it, is given
+in the following @code{MODULE}:
+
+@smallexample
+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
+@end smallexample
+
+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:
+
+@smallexample
+int
+call_it (int (*func)(int), int arg)
+@{
+ return func (arg);
+@}
+@end smallexample
+
+It can be used as in the following Fortran code:
+
+@smallexample
+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
+@end smallexample
+
+@node Further Interoperability of Fortran with C
+@subsection Further Interoperability of Fortran with C
+
+Assumed-shape and allocatable arrays are passed using an array descriptor
+(dope vector). The internal structure of the array descriptor used
+by GNU Fortran is not yet documented and will change. There will also be
+a Technical Report (TR 29113) which standardizes an interoperable
+array descriptor. Until then, you can use the Chasm Language
+Interoperability Tools, @url{http://chasm-interop.sourceforge.net/},
+which provide an interface to GNU Fortran's array descriptor.
+
+The technical report 29113 will presumably also include support for
+C-interoperable @code{OPTIONAL} and for assumed-rank and assumed-type
+dummy arguments. However, the TR has neither been approved nor implemented
+in GNU Fortran; therefore, these features are not yet available.
+
+
+
+@node GNU Fortran Compiler Directives
+@section GNU Fortran Compiler Directives
+
+The Fortran standard 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
+@ref{Top,,C Extensions,gcc,Using the GNU Compiler Collection (GCC)}
+for details.
+
+For procedures and procedure pointers, the following attributes can
+be used to change the calling convention:
+
+@itemize
+@item @code{CDECL} -- standard C calling convention
+@item @code{STDCALL} -- convention where the called procedure pops the stack
+@item @code{FASTCALL} -- part of the arguments are passed via registers
+instead using the stack
+@end itemize
+
+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
+@code{COMMON} blocks) need special handling to be accessible when they
+are in a shared library. The following attributes are available:
+
+@itemize
+@item @code{DLLEXPORT} -- provide a global pointer to a pointer in the DLL
+@item @code{DLLIMPORT} -- reference the function or variable using a global pointer
+@end itemize
+
+The attributes are specified using the syntax
+
+@code{!GCC$ ATTRIBUTES} @var{attribute-list} @code{::} @var{variable-list}
+
+where in free-form source code only whitespace is allowed before @code{!GCC$}
+and in fixed-form source code @code{!GCC$}, @code{cGCC$} or @code{*GCC$} 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.
+
+
+
+@node Non-Fortran Main Program
+@section Non-Fortran Main Program
+
+@menu
+* _gfortran_set_args:: Save command-line arguments
+* _gfortran_set_options:: Set library option flags
+* _gfortran_set_convert:: Set endian conversion
+* _gfortran_set_record_marker:: Set length of record markers
+* _gfortran_set_max_subrecord_length:: Set subrecord length
+* _gfortran_set_fpe:: Set when a Floating Point Exception should be raised
+@end menu
+
+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 @code{PROGRAM} with GNU Fortran, a function
+with the name @code{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 @code{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 @code{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 @code{_gfortran_set_args} and
+@code{_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 @code{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.
+
+
+@node _gfortran_set_args
+@subsection @code{_gfortran_set_args} --- Save command-line arguments
+@fnindex _gfortran_set_args
+@cindex libgfortran initialization, set_args
+
+@table @asis
+@item @emph{Description}:
+@code{_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 @code{_gfortran_set_options}).
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_args (int argc, char *argv[])}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{argc} @tab number of command line argument strings
+@item @var{argv} @tab the command-line argument strings; argv[0]
+is the pathname of the executable itself.
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_options
+@subsection @code{_gfortran_set_options} --- Set library option flags
+@fnindex _gfortran_set_options
+@cindex libgfortran initialization, set_options
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_options} sets several flags related to the Fortran
+standard to be used, whether backtracing or core dumps 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
+@pxref{Code Gen Options}. Please note that not all flags are actually
+used.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_options (int num, int options[])}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{num} @tab number of options passed
+@item @var{argv} @tab The list of flag values
+@end multitable
+
+@item @emph{option flag list}:
+@multitable @columnfractions .15 .70
+@item @var{option}[0] @tab 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) @code{GFC_STD_F77} (1),
+@code{GFC_STD_F95_OBS} (2), @code{GFC_STD_F95_DEL} (4), @code{GFC_STD_F95}
+(8), @code{GFC_STD_F2003} (16), @code{GFC_STD_GNU} (32),
+@code{GFC_STD_LEGACY} (64), @code{GFC_STD_F2008} (128), and
+@code{GFC_STD_F2008_OBS} (256). Default: @code{GFC_STD_F95_OBS
+| GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003 | GFC_STD_F2008
+| GFC_STD_F2008_OBS | GFC_STD_F77 | GFC_STD_GNU | GFC_STD_LEGACY}.
+@item @var{option}[1] @tab Standard-warning flag; prints a warning to
+standard error. Default: @code{GFC_STD_F95_DEL | GFC_STD_LEGACY}.
+@item @var{option}[2] @tab If non zero, enable pedantic checking.
+Default: off.
+@item @var{option}[3] @tab If non zero, enable core dumps on run-time
+errors. Default: off.
+@item @var{option}[4] @tab If non zero, enable backtracing on run-time
+errors. Default: off.
+Note: Installs a signal handler and requires command-line
+initialization using @code{_gfortran_set_args}.
+@item @var{option}[5] @tab If non zero, supports signed zeros.
+Default: enabled.
+@item @var{option}[6] @tab 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 (16), GFC_RTCHECK_POINTER (32).
+Default: disabled.
+@item @var{option}[7] @tab If non zero, range checking is enabled.
+Default: enabled. See -frange-check (@pxref{Code Gen Options}).
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+ /* Use gfortran 4.5 default options. */
+ static int options[] = @{68, 255, 0, 0, 0, 1, 0, 1@};
+ _gfortran_set_options (8, &options);
+@end smallexample
+@end table
+
+
+@node _gfortran_set_convert
+@subsection @code{_gfortran_set_convert} --- Set endian conversion
+@fnindex _gfortran_set_convert
+@cindex libgfortran initialization, set_convert
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_convert} set the representation of data for
+unformatted files.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_convert (int conv)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{conv} @tab Endian conversion, possible values:
+GFC_CONVERT_NATIVE (0, default), GFC_CONVERT_SWAP (1),
+GFC_CONVERT_BIG (2), GFC_CONVERT_LITTLE (3).
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ _gfortran_set_convert (1);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_record_marker
+@subsection @code{_gfortran_set_record_marker} --- Set length of record markers
+@fnindex _gfortran_set_record_marker
+@cindex libgfortran initialization, set_record_marker
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_record_marker} sets the length of record markers
+for unformatted files.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_record_marker (int val)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{val} @tab Length of the record marker; valid values
+are 4 and 8. Default is 4.
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ _gfortran_set_record_marker (8);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_fpe
+@subsection @code{_gfortran_set_fpe} --- Set when a Floating Point Exception should be raised
+@fnindex _gfortran_set_fpe
+@cindex libgfortran initialization, set_fpe
+
+@table @asis
+@item @emph{Description}:
+@code{_gfortran_set_fpe} sets the IEEE exceptions for which a
+Floating Point Exception (FPE) should be raised. On most systems,
+this will result in a SIGFPE signal being sent and the program
+being interrupted.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_fpe (int val)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{option}[0] @tab IEEE exceptions. Possible values are
+(bitwise or-ed) zero (0, default) no trapping,
+@code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2),
+@code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8),
+@code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_PRECISION} (32).
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+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;
+@}
+@end smallexample
+@end table
+
+
+@node _gfortran_set_max_subrecord_length
+@subsection @code{_gfortran_set_max_subrecord_length} --- Set subrecord length
+@fnindex _gfortran_set_max_subrecord_length
+@cindex libgfortran initialization, set_max_subrecord_length
+
+@table @asis
+@item @emph{Description}:
+@code{_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.
+
+@item @emph{Syntax}:
+@code{void _gfortran_set_max_subrecord_length (int val)}
+
+@item @emph{Arguments}:
+@multitable @columnfractions .15 .70
+@item @var{val} @tab the maximum length for a subrecord;
+the maximum permitted value is 2147483639, which is also
+the default.
+@end multitable
+
+@item @emph{Example}:
+@smallexample
+int main (int argc, char *argv[])
+@{
+ /* Initialize libgfortran. */
+ _gfortran_set_args (argc, argv);
+ _gfortran_set_max_subrecord_length (8);
+ return 0;
+@}
+@end smallexample
+@end table
+
+
+
+@c Intrinsic Procedures
@c ---------------------------------------------------------------------
+@include intrinsic.texi
+
+
+@tex
+\blankpart
+@end tex
+
@c ---------------------------------------------------------------------
@c Contributing
@c ---------------------------------------------------------------------
@node Contributing
-@chapter Contributing
+@unnumbered Contributing
@cindex Contributing
Free software is only possible if people contribute to efforts
We're always in need of more people helping out with ideas
and comments, writing documentation and contributing code.
-If you want to contribute to GNU Fortran 95,
+If you want to contribute to GNU Fortran,
have a look at the long lists of projects you can take on.
Some of these projects are small,
some of them are large;
some are completely orthogonal to the rest of what is
-happening on @command{gfortran},
+happening on GNU Fortran,
but others are ``mainstream'' projects in need of enthusiastic hackers.
All of these projects are important!
We'll eventually get around to the things here,
@menu
* Contributors::
* Projects::
+* Proposed Extensions::
@end menu
@node Contributors
-@section Contributors to GNU Fortran 95
+@section Contributors to GNU Fortran
@cindex Contributors
@cindex Credits
@cindex Authors
Most of the interface with GCC was written by @emph{Paul Brook}.
The following individuals have contributed code and/or
-ideas and significant help to the gfortran project
-(in no particular order):
+ideas and significant help to the GNU Fortran project
+(in alphabetical order):
@itemize @minus
-@item Andy Vaught
-@item Katherine Holcomb
-@item Tobias Schlüter
+@item Janne Blomqvist
@item Steven Bosscher
-@item Toon Moene
-@item Tim Prince
-@item Niels Kristian Bech Jensen
-@item Steven Johnson
@item Paul Brook
-@item Feng Wang
+@item Tobias Burnus
+@item Fran@,{c}ois-Xavier Coudert
@item Bud Davis
-@item Paul Thomas
-@item François-Xavier Coudert
-@item Steve Kargl
-@item Jerry Delisle
-@item Janne Blomqvist
+@item Jerry DeLisle
@item Erik Edelmann
+@item Bernhard Fischer
+@item Daniel Franke
+@item Richard Guenther
+@item Richard Henderson
+@item Katherine Holcomb
+@item Jakub Jelinek
+@item Niels Kristian Bech Jensen
+@item Steven Johnson
+@item Steven G. Kargl
@item Thomas Koenig
@item Asher Langton
+@item H. J. Lu
+@item Toon Moene
+@item Brooks Moses
+@item Andrew Pinski
+@item Tim Prince
+@item Christopher D. Rickett
+@item Richard Sandiford
+@item Tobias Schl@"uter
+@item Roger Sayle
+@item Paul Thomas
+@item Andy Vaught
+@item Feng Wang
+@item Janus Weil
+@item Daniel Kraft
@end itemize
The following people have contributed bug reports,
smaller or larger patches,
and much needed feedback and encouragement for the
-@command{gfortran} project:
+GNU Fortran project:
@itemize @minus
-@item Erik Schnetter
@item Bill Clodius
+@item Dominique d'Humi@`eres
@item Kate Hedstrom
+@item Erik Schnetter
+@item Joost VandeVondele
@end itemize
Many other individuals have helped debug,
-test and improve @command{gfortran} over the past few years,
+test and improve the GNU Fortran compiler over the past few years,
and we welcome you to do the same!
If you already have done so,
and you would like to see your name listed in the
@table @emph
@item Help build the test suite
-Solicit more code for donation to the test suite.
-We can keep code private on request.
+Solicit more code for donation to the test suite: the more extensive the
+testsuite, the smaller the risk of breaking things in the future! We can
+keep code private on request.
@item Bug hunting/squishing
-Find bugs and write more test cases!
-Test cases are especially very welcome,
-because it allows us to concentrate on fixing bugs
-instead of isolating them.
-
-@item Smaller projects (``bug'' fixes):
- @itemize @minus
- @item Allow init exprs to be numbers raised to integer powers.
- @item Implement correct rounding.
- @item Implement F restrictions on Fortran 95 syntax.
- @item See about making Emacs-parsable error messages.
- @end itemize
+Find bugs and write more test cases! Test cases are especially very
+welcome, because it allows us to concentrate on fixing bugs instead of
+isolating them. Going through the bugzilla database at
+@url{http://gcc.gnu.org/@/bugzilla/} to reduce testcases posted there and
+add more information (for example, for which version does the testcase
+work, for which versions does it fail?) is also very helpful.
+
@end table
-If you wish to work on the runtime libraries,
-please contact a project maintainer.
-@c TODO: email!
+@node Proposed Extensions
+@section Proposed Extensions
-@c ---------------------------------------------------------------------
-@c Standards
-@c ---------------------------------------------------------------------
+Here's a list of proposed extensions for the GNU Fortran compiler, in no particular
+order. Most of these are necessary to be fully compatible with
+existing Fortran compilers, but they are not part of the official
+J3 Fortran 95 standard.
-@node Standards
-@chapter Standards
-@cindex Standards
+@subsection Compiler extensions:
+@itemize @bullet
+@item
+User-specified alignment rules for structures.
-The GNU Fortran 95 Compiler aims to be a conforming implementation of
-ISO/IEC 1539:1997 (Fortran 95).
+@item
+Automatically extend single precision constants to double.
-In the future it may also support other variants of and extensions to
-the Fortran language. These include ANSI Fortran 77, ISO Fortran 90,
-ISO Fortran 2003 and OpenMP.
+@item
+Compile code that conserves memory by dynamically allocating common and
+module storage either on stack or heap.
-@menu
-* Fortran 2003 status::
-@end menu
+@item
+Compile flag to generate code for array conformance checking (suggest -CC).
-@node Fortran 2003 status
-@section Fortran 2003 status
+@item
+User control of symbol names (underscores, etc).
-Although @command{gfortran} focuses on implementing the Fortran 95
-standard for the time being, a few Fortran 2003 features are currently
-available.
+@item
+Compile setting for maximum size of stack frame size before spilling
+parts to static or heap.
-@itemize
-@item
-Intrinsics @code{command_argument_count}, @code{get_command},
-@code{get_command_argument}, and @code{get_environment_variable}.
+@item
+Flag to force local variables into static space.
-@item
-@cindex Array constructors
-@cindex @code{[...]}
-Array constructors using square brackets. That is, @code{[...]} rather
-than @code{(/.../)}.
+@item
+Flag to force local variables onto stack.
+@end itemize
+
+@subsection Environment Options
+@itemize @bullet
@item
-@cindex @code{FLUSH} statement
-@code{FLUSH} statement.
+Pluggable library modules for random numbers, linear algebra.
+LA should use BLAS calling conventions.
@item
-@cindex @code{IOMSG=} specifier
-@code{IOMSG=} specifier for I/O statements.
+Environment variables controlling actions on arithmetic exceptions like
+overflow, underflow, precision loss---Generate NaN, abort, default.
+action.
@item
-@cindex @code{ENUM} statement
-@cindex @code{ENUMERATOR} statement
-@cindex @command{-fshort-enums}
-Support for the declaration of enumeration constants via the
-@code{ENUM} and @code{ENUMERATOR} statements. Interoperability with
-@command{gcc} is guaranteed also for the case where the
-@command{-fshort-enums} command line option is given.
+Set precision for fp units that support it (i387).
@item
-@cindex TR 15581
-The following parts of TR 15581:
-@itemize
+Variable for setting fp rounding mode.
+
@item
-@cindex @code{ALLOCATABLE} dummy arguments
-The @code{ALLOCATABLE} attribute for dummy arguments.
+Variable to fill uninitialized variables with a user-defined bit
+pattern.
+
@item
-@cindex @code{ALLOCATABLE} function results
-@code{ALLOCATABLE} function results
-@end itemize
+Environment variable controlling filename that is opened for that unit
+number.
+
+@item
+Environment variable to clear/trash memory being freed.
+
+@item
+Environment variable to control tracing of allocations and frees.
+
+@item
+Environment variable to display allocated memory at normal program end.
+
+@item
+Environment variable for filename for * IO-unit.
+
+@item
+Environment variable for temporary file directory.
+
+@item
+Environment variable forcing standard output to be line buffered (unix).
@end itemize
@c GNU General Public License
@c ---------------------------------------------------------------------
-@include gpl.texi
+@include gpl_v3.texi
@include funding.texi
@c ---------------------------------------------------------------------
-@c Index
+@c Indices
@c ---------------------------------------------------------------------
-@node Index
-@unnumbered Index
-
+@node Option Index
+@unnumbered Option Index
+@command{gfortran}'s command line options are indexed here without any
+initial @samp{-} or @samp{--}. Where an option has both positive and
+negative forms (such as -foption and -fno-option), relevant entries in
+the manual are indexed under the most appropriate form; it may sometimes
+be useful to look up both forms.
+@printindex op
+
+@node Keyword Index
+@unnumbered Keyword Index
@printindex cp
@bye
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