\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename gfortran.info
-@set copyrights-gfortran 1999-2008
+@set copyrights-gfortran 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
@include gcc-common.texi
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 1.2 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 ``Funding Free Software'', the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
@cindex Introduction
This manual documents the use of @command{gfortran},
-the GNU Fortran compiler. You can find in this manual how to invoke
+the GNU Fortran compiler. You can find in this manual how to invoke
@command{gfortran}, as well as its features and incompatibilities.
@ifset DEVELOPMENT
Part II: Language Reference
* Fortran 2003 and 2008 status:: Fortran 2003 and 2008 features supported by GNU Fortran.
-* Compiler Characteristics:: KIND type parameters supported.
+* 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.
@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},
+compiler. You can find in this manual how to invoke @command{gfortran},
as well as its features and incompatibilities.
@ifset DEVELOPMENT
@node About GNU Fortran
@section About GNU Fortran
-The GNU Fortran compiler is still in an early state of development.
-It can generate code for most constructs and expressions,
-but much work remains to be done.
-
-When the GNU Fortran compiler is finished,
-it will do everything you expect from any decent compiler:
+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
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
+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}
+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{.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}
+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
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
+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 @code{.F}, @code{.FOR}, @code{.FTN}, @code{.fpp},
-@code{.FPP}, @code{.F90}, @code{.F95}, @code{.F03} or @code{.F08}. To manually
+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
+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.
+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://users.erols.com/dnagle/coco.html}).
+supported by the GNU Fortran compiler. You can use the program coco
+to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}).
@c ---------------------------------------------------------------------
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 such as enumeration, stream I/O, and some of the
-enhancements to allocatable array support from TR 15581. However, it is
-still under development and has a few remaining rough edges.
+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,
@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
+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
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.
+future standards---in particular, Fortran 2003 and Fortran 2008.
@c ---------------------------------------------------------------------
@section Standards
@cindex Standards
+@menu
+* Varying Length Character Strings::
+@end menu
+
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, and
-the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
-OpenMP Application Program Interface v2.5} specification.
+the ISO/IEC TR-15581 enhancements to allocatable arrays.
In the future, the GNU Fortran compiler will also support ISO/IEC
-1539-1:2004 (Fortran 2003) and future Fortran standards. Partial support
-of that standard is already provided; the current status of Fortran 2003
-support is reported in the @ref{Fortran 2003 status} section of the
-documentation.
+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.
+
+Additionally, the GNU Fortran compilers supports the OpenMP specification
+(version 3.0, @url{http://openmp.org/@/wp/@/openmp-specifications/}).
+
+@node Varying Length Character Strings
+@subsection Varying Length Character Strings
+@cindex Varying length character strings
+@cindex Varying length strings
+@cindex strings, varying length
+
+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/}.
-The next version of the Fortran standard after Fortran 2003 is currently
-being developed and the GNU Fortran compiler supports some of its new
-features. This support is based on the latest draft of the standard
-(available from @url{http://www.nag.co.uk/sc22wg5/}) and no guarantee of
-future compatibility is made, as the final standard might differ from the
-draft. For more information, see the @ref{Fortran 2008 status} section.
@c =====================================================================
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,
-GNU Fortran 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 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
+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.
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
+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.
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
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
+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.
@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
+@samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
unless the @option{-fbacktrace} compile option
was used.
@node Fortran 2003 status
@section Fortran 2003 status
-Although GNU Fortran focuses on implementing the Fortran 95
-standard for the time being, a few Fortran 2003 features are currently
-available.
+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.
@itemize
@item
@item
@cindex array, constructors
@cindex @code{[...]}
-Array constructors using square brackets. That is, @code{[...]} rather
-than @code{(/.../)}.
+Array constructors using square brackets. That is, @code{[...]} rather
+than @code{(/.../)}. Type-specification for array constructors like
+@code{(/ some-type :: ... /)}.
@item
@cindex @code{FLUSH} statement
@end itemize
@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.
+
+@item
@cindex @code{STREAM} I/O
@cindex @code{ACCESS='STREAM'} I/O
The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier,
Interoperability with C (ISO C Bindings)
@item
-BOZ as argument of INT, REAL, DBLE and CMPLX.
+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 next version of the Fortran standard after Fortran 2003 is currently
-being worked on by the Working Group 5 of Sub-Committee 22 of the Joint
-Technical Committee 1 of the International Organization for
-Standardization (ISO) and the International Electrotechnical Commission
-(IEC). This group is known at @uref{http://www.nag.co.uk/sc22wg5/, WG5}.
-The next revision of the Fortran standard is informally referred to as
-Fortran 2008, reflecting its planned release year. The GNU Fortran
-compiler has support for some of the new features in Fortran 2008. This
-support is based on the latest draft, available from
-@url{http://www.nag.co.uk/sc22wg5/}. However, as the final standard may
-differ from the drafts, no guarantee of backward compatibility can be
-made and you should only use it for experimental purposes.
+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 of the intrinsic module @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 ---------------------------------------------------------------------
@node Compiler Characteristics
@chapter Compiler Characteristics
-@c TODO: Formulate this introduction a little more generally once
-@c there is more here than KIND type parameters.
-
-This chapter describes certain characteristics of the GNU Fortran compiler,
-namely the KIND type parameter values supported.
+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
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 ---------------------------------------------------------------------
@cindex extensions, implemented
GNU Fortran implements a number of extensions over standard
-Fortran. This chapter contains information on their syntax and
+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
@subsection Old-style kind specifications
@cindex kind, old-style
-GNU Fortran allows old-style kind specifications in declarations. These
+GNU Fortran allows old-style kind specifications in declarations. These
look like:
@smallexample
TYPESPEC*size x,y,z
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
+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
@cindex BOZ literal constants
Besides decimal constants, Fortran also supports binary (@code{b}),
-octal (@code{o}) and hexadecimal (@code{z}) integer constants. The
+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'}.)
+@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
+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,
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
+@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.
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
+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}
+(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.
ipt = loc(target)
@end smallexample
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
+@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
+assumptions is illegal. It is the user's responsibility to avoid doing
this; the compiler works under the assumption that no such aliasing
occurs.
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
+@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.
-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.
+@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:
and environment variables that influence run-time behavior.
GNU Fortran strives to be compatible to the
-@uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf,
-OpenMP Application Program Interface v2.5}.
+@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
+@option{-fopenmp}. This also arranges for automatic linking of the
GNU OpenMP runtime library @ref{Top,,libgomp,libgomp,GNU OpenMP
runtime library}.
@itemize
@item
@option{-fopenmp} implies @option{-frecursive}, i.e., all local arrays
-will be allocated on the stack. When porting existing code to OpenMP,
+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 can not be statically
-linked due to limitations of the underlying pthreads-implementation. It
+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
+to the command line. However, this is not supported by @command{gcc} and
thus not recommended.
@end itemize
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
+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
+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.
+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
@end smallexample
For details refer to the g77 manual
-@uref{http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top}.
-
-Also, the gfortran testsuite c_by_val.f and its partner c_by_val.c are
-worth a look.
+@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
@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 -- the list of Fortran and libgfortran bugs closed as WONTFIX:
@c http://tinyurl.com/2u4h5y
@menu
@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:
+@c * Omitted arguments in procedure call::
+* Alternate complex function syntax::
@end menu
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
+``derived types''. Here is an example of code using the non portable
structure syntax:
@example
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
+Fortran 77. For example, replace a code fragment like
@smallexample
INTEGER*1 LINE(80)
with the following:
@smallexample
- INTEGER*1 LINE(80)
+ CHARACTER(LEN=80) LINE
REAL A, B, C
c ... Code that sets A, B and C
WRITE (UNIT=LINE, FMT=9000) A, B, C
@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
+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,
+standard) combination of internal output and string formats. For example,
replace a code fragment like this:
@smallexample
@smallexample
c Variable declaration
- CHARACTER(LEN=20) F
+ CHARACTER(LEN=20) FMT
c
c Other code here...
c
WRITE(FMT,'("(I", I0, ")")') N+1
- WRITE(6,FM) INT1
+ WRITE(6,FMT) INT1
@end smallexample
@noindent
@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.
+
+@c ---------------------------------------------------------------------
+@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 ---------------------------------------------------------------------
@item Andy Vaught
@item Feng Wang
@item Janus Weil
+@item Daniel Kraft
@end itemize
The following people have contributed bug reports,
@item Dominique d'Humi@`eres
@item Kate Hedstrom
@item Erik Schnetter
+@item Joost VandeVondele
@end itemize
Many other individuals have helped debug,
@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. Going through the bugzilla database at
-@url{http://gcc.gnu.org/bugzilla/} to reduce testcases posted there and
+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.
User-specified alignment rules for structures.
@item
-Flag to generate @code{Makefile} info.
-
-@item
Automatically extend single precision constants to double.
@item
@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
+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.
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