@@ -219,17 +219,9 @@ 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 will use to invoke the compiler.
-
@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
@@ -241,46 +233,67 @@ or alternative to, the Unix @command{f95} command;
@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, 2008 and 2018 standards, and
-several vendor extensions. The development goal is to provide the
-following features:
+The GNU Fortran compiler is the successor to @command{g77}, the
+Fortran 77 front end included in GCC prior to version 4 (released in
+2005). While it is backward-compatible with most @command{g77}
+extensions and command-line options, @command{gfortran} is a completely new
+implemention designed to support more modern dialects of Fortran.
+GNU Fortran implements the Fortran 77, 90 and 95 standards
+completely, most of the Fortran 2003 and 2008 standards, and some
+features from the 2018 standard. It also implements several extensions
+including OpenMP and OpenACC support for parallel programming.
+
+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{https://polyhedron.com/?page_id=175,
+Polyhedron Fortran compiler benchmarks} and the
+@uref{http://www.netlib.org/benchmark/livermore,
+Livermore Fortran Kernels test}. It has been used to compile a number of
+large real-world programs, including
+@uref{http://hirlam.org/, the HARMONIE and HIRLAM weather forecasting code} and
+@uref{https://github.com/dylan-jayatilaka/tonto,
+the Tonto quantum chemistry package}; see
+@url{https://gcc.gnu.org/@/wiki/@/GfortranApps} for an extended list.
+
+GNU Fortran provides the following functionality:
@itemize @bullet
@item
-Read a user's program, stored in a file and containing instructions
-written in Fortran 77, Fortran 90, Fortran 95, Fortran 2003, Fortran
-2008 or Fortran 2018. This file contains @dfn{source code}.
+Read a program, stored in a file and containing @dfn{source code}
+instructions written in Fortran 77.
@item
-Translate the user's program into instructions a computer
+Translate the program into instructions a computer
can carry out more quickly than it takes to translate the
-instructions in the first
-place. The result after compilation of a program is
+original Fortran instructions.
+The result after compilation of a program is
@dfn{machine code},
-code designed to be efficiently translated and processed
+which is efficiently translated and processed
by a machine such as your computer.
Humans usually are not as good writing machine code
as they are at writing Fortran (or C++, Ada, or Java),
because it is easy to make tiny mistakes writing machine code.
@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.
-The Fortran 90 standard requires that the compiler can point out
-mistakes to the user.
+Provide information about the reasons why
+the compiler may be unable to create a binary from the source code,
+for example if the source code is flawed.
+The Fortran language standards require that the compiler can point out
+mistakes in your code.
An incorrect usage of the language causes an @dfn{error message}.
-The compiler will also attempt to diagnose cases where the
-user's program contains a correct usage of the language,
+The compiler also attempts to diagnose cases where your
+program contains a correct usage of the language,
but instructs the computer to do something questionable.
-This kind of diagnostics message is called a @dfn{warning message}.
+This kind of diagnostic message is called a @dfn{warning message}.
@item
Provide optional information about the translation passes
from the source code to machine code.
-This can help a user of the compiler to find the cause of
+This can help you to find the cause of
certain bugs which may not be obvious in the source code,
but may be more easily found at a lower level compiler output.
It also helps developers to find bugs in the compiler itself.
@@ -292,7 +305,7 @@ called a @dfn{debugger}, such as the GNU Debugger @command{gdb}).
@item
Locate and gather machine code already generated to
-perform actions requested by statements in the user's program.
+perform actions requested by statements in the program.
This machine code is organized into @dfn{modules} and is located
and @dfn{linked} to the user program.
@end itemize
@@ -316,8 +329,9 @@ which also might be installed as the
system's @command{f95} command.
@command{gfortran} is just another driver program,
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.
+The primary difference between the @command{gcc} and @command{gfortran}
+commands is that the latter automatically links the correct libraries
+to your program.
@item
A collection of run-time libraries.
@@ -338,7 +352,7 @@ linked to and interfaced with the GCC backend library.
assembler code. You would typically not use this
program directly;
instead, the @command{gcc} or @command{gfortran} driver
-programs will call it for you.
+programs call it for you.
@end itemize
@@ -364,10 +378,10 @@ 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},
+GCC that has been compiled with Fortran language support enabled,
+@command{gcc} recognizes 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 compiles 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.
@@ -382,138 +396,12 @@ 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
+that 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.
-
-@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. The macros @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.
-
-GNU Fortran supports a number of @code{INTEGER} and @code{REAL} kind types
-in additional to the kind types required by the Fortran standard.
-The availability of any given kind type is architecture dependent. The
-following pre-defined preprocessor macros can be used to conditionally
-include code for these additional kind types: @code{__GFC_INT_1__},
-@code{__GFC_INT_2__}, @code{__GFC_INT_8__}, @code{__GFC_INT_16__},
-@code{__GFC_REAL_10__}, and @code{__GFC_REAL_16__}.
-
-While CPP is the de-facto standard for preprocessing Fortran code,
-Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
-Conditional Compilation, which is not widely used and not directly
-supported by the GNU Fortran compiler. You can use the program coco
-to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}).
-
-
-@c ---------------------------------------------------------------------
-@c GNU Fortran and G77
-@c ---------------------------------------------------------------------
-
-@node GNU Fortran and G77
-@section GNU Fortran and G77
-@cindex Fortran 77
-@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}.
-
-
-@c ---------------------------------------------------------------------
-@c Project Status
-@c ---------------------------------------------------------------------
-
-@node Project Status
-@section Project Status
-
-@quotation
-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 @command{gfortran} is done,
-we'll see if it will be a beautiful butterfly,
-or just a big bug....
-
---Andy Vaught, April 2000
-@end quotation
-
-The start of the GNU Fortran 95 project was announced on
-the GCC homepage in March 18, 2000
-(even though Andy had already been working on it for a while,
-of course).
-
-The GNU Fortran compiler is able to compile nearly all
-standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs,
-including a number of standard and non-standard extensions, and can be
-used on real-world programs. In particular, the supported extensions
-include OpenMP, Cray-style pointers, some old vendor extensions, and several
-Fortran 2003 and Fortran 2008 features, including TR 15581. However, it is
-still under development and has a few remaining rough edges.
-There also is initial support for OpenACC.
-
-At present, the GNU Fortran compiler passes the
-@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/fortran-compiler-comparisons/polyhedron-benchmark-suite,
-Polyhedron Fortran
-compiler benchmarks} and the
-@uref{http://www.netlib.org/benchmark/livermore,
-Livermore Fortran Kernels test}. It has been used to compile a number of
-large real-world programs, including
-@uref{http://hirlam.org/, the HARMONIE and HIRLAM weather forecasting code} and
-@uref{http://physical-chemistry.scb.uwa.edu.au/tonto/wiki/index.php/Main_Page,
-the Tonto quantum chemistry package}; see
-@url{https://gcc.gnu.org/@/wiki/@/GfortranApps} for an extended list.
-
-Among other things, the GNU Fortran compiler is intended as a replacement
-for G77. At this point, nearly all programs that could be compiled with
-G77 can be compiled with GNU Fortran, although there are a few minor known
-regressions.
-
-The primary work remaining to be done on GNU Fortran falls into three
-categories: bug fixing (primarily regarding the treatment of invalid
-code and providing useful error messages), improving the compiler
-optimizations and the performance of compiled code, and extending the
-compiler to support future standards---in particular, Fortran 2003,
-Fortran 2008 and Fortran 2018.
-
-
@c ---------------------------------------------------------------------
@c Standards
@c ---------------------------------------------------------------------
@@ -529,18 +417,27 @@ Fortran 2008 and Fortran 2018.
* Fortran 2018 status::
@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.
-
-GNU Fortran also have a partial support for ISO/IEC 1539-1:2004
-(Fortran 2003), ISO/IEC 1539-1:2010 (Fortran 2008), the Technical
-Specification @code{Further Interoperability of Fortran with C}
-(ISO/IEC TS 29113:2012). Full support of those standards and future
-Fortran standards is planned. The current status of the support is
-can be found in the @ref{Fortran 2003 status}, @ref{Fortran 2008
-status} and @ref{Fortran 2018 status} sections of the documentation.
+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}.
+Official Fortran standard documents are available for purchase
+from ISO; a collection of free documents (typically final drafts) are
+also available on the @uref{https://gcc.gnu.org/wiki/GFortranStandards, wiki}.
+
+The GNU Fortran compiler implements ISO/IEC 1539:1997 (Fortran 95).
+As such, it can also compile essentially all standard-compliant
+Fortran 90 and Fortran 77 programs. It also supports the ISO/IEC
+TR-15581 enhancements to allocatable arrays.
+
+GNU Fortran also supports almost all of ISO/IEC 1539-1:2004
+(Fortran 2003) and ISO/IEC 1539-1:2010 (Fortran 2008).
+It has partial support for features introduced in ISO/IEC
+1539:2018 (Fortran 2018), the most recent version of the Fortran
+language standard, including full support for the Technical Specification
+@code{Further Interoperability of Fortran with C} (ISO/IEC TS 29113:2012).
+More details on support for these standards can be
+found in the following sections of the documentation.
Additionally, the GNU Fortran compilers supports the OpenMP specification
(version 4.5 and partial support of the features of the 5.0 version,
@@ -551,9 +448,9 @@ version 2.6, @uref{http://www.openacc.org/}). See
@node Fortran 95 status
@subsection Fortran 95 status
-@cindex Varying length character strings
@cindex Varying length strings
@cindex strings, varying length
+@cindex conditional compilation
The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000)
varying length character strings. While GNU Fortran currently does not
@@ -567,377 +464,93 @@ the features of @code{ISO_VARYING_STRING} and should be considered as
replacement. (Namely, allocatable or pointers of the type
@code{character(len=:)}.)
+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}).
+
@node Fortran 2003 status
@subsection Fortran 2003 status
-GNU Fortran supports several Fortran 2003 features; an incomplete
-list can be found below. See also the
-@uref{https://gcc.gnu.org/wiki/Fortran2003, wiki page} about Fortran 2003.
-
-@itemize
-@item Procedure pointers including procedure-pointer components with
-@code{PASS} attribute.
-
-@item Procedures which are bound to a derived type (type-bound procedures)
-including @code{PASS}, @code{PROCEDURE} and @code{GENERIC}, and
-operators bound to a type.
-
-@item Abstract interfaces and type extension with the possibility to
-override type-bound procedures or to have deferred binding.
-
-@item Polymorphic entities (``@code{CLASS}'') for derived types and unlimited
-polymorphism (``@code{CLASS(*)}'') -- including @code{SAME_TYPE_AS},
-@code{EXTENDS_TYPE_OF} and @code{SELECT TYPE} for scalars and arrays and
-finalization.
-
-@item Generic interface names, which have the same name as derived types,
-are now supported. This allows one to write constructor functions. Note
-that Fortran does not support static constructor functions. For static
-variables, only default initialization or structure-constructor
-initialization are available.
-
-@item The @code{ASSOCIATE} construct.
-
-@item Interoperability with C including enumerations,
-
-@item In structure constructors the components with default values may be
-omitted.
-
-@item Extensions to the @code{ALLOCATE} statement, allowing for a
-type-specification with type parameter and for allocation and initialization
-from a @code{SOURCE=} expression; @code{ALLOCATE} and @code{DEALLOCATE}
-optionally return an error message string via @code{ERRMSG=}.
+GNU Fortran implements the Fortran 2003 (ISO/IEC 1539-1:2004) standard
+except for finalization support, which is incomplete.
+See the
+@uref{https://gcc.gnu.org/wiki/Fortran2003, wiki page} for a full list
+of new features introduced by Fortran 2003 and their implementation status.
-@item Reallocation on assignment: If an intrinsic assignment is
-used, an allocatable variable on the left-hand side is automatically allocated
-(if unallocated) or reallocated (if the shape is different). Currently, scalar
-deferred character length left-hand sides are correctly handled but arrays
-are not yet fully implemented.
-
-@item Deferred-length character variables and scalar deferred-length character
-components of derived types are supported. (Note that array-valued components
-are not yet implemented.)
-
-@item Transferring of allocations via @code{MOVE_ALLOC}.
-
-@item The @code{PRIVATE} and @code{PUBLIC} attributes may be given individually
-to derived-type components.
-
-@item In pointer assignments, the lower bound may be specified and
-the remapping of elements is supported.
-
-@item For pointers an @code{INTENT} may be specified which affect the
-association status not the value of the pointer target.
-
-@item Intrinsics @code{command_argument_count}, @code{get_command},
-@code{get_command_argument}, and @code{get_environment_variable}.
-
-@item Support for Unicode characters (ISO 10646) and UTF-8, including
-the @code{SELECTED_CHAR_KIND} and @code{NEW_LINE} intrinsic functions.
-
-@item Support for binary, octal and hexadecimal (BOZ) constants in the
-intrinsic functions @code{INT}, @code{REAL}, @code{CMPLX} and @code{DBLE}.
-
-@item Support for namelist variables with allocatable and pointer
-attribute and nonconstant length type parameter.
-
-@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 :: ... /)}.
-
-@item Extensions to the specification and initialization expressions,
-including the support for intrinsics with real and complex arguments.
-
-@item Support for the asynchronous input/output.
-
-@item
-@cindex @code{FLUSH} statement
-@cindex statement, @code{FLUSH}
-@code{FLUSH} statement.
+@node Fortran 2008 status
+@subsection Fortran 2008 status
-@item
-@cindex @code{IOMSG=} specifier
-@code{IOMSG=} specifier for I/O statements.
+The GNU Fortran compiler supports almost all features of Fortran 2008;
+the @uref{https://gcc.gnu.org/wiki/Fortran2008Status, wiki}
+has some information about the current implementation status.
+In particular, the following are not yet supported:
+@itemize @bullet
@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.
+@code{DO CONCURRENT} and @code{FORALL} do not recognize a
+type-spec in the loop header.
@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
+The change to permit any constant expression in subscripts and
+nested implied-do limits in a @code{DATA} statement has not been implemented.
@end itemize
-@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.
-@item
-Namelist input/output for internal files.
+@node Fortran 2018 status
+@subsection Fortran 2018 status
-@item Minor I/O features: Rounding during formatted output, using of
-a decimal comma instead of a decimal point, setting whether a plus sign
-should appear for positive numbers. On systems where @code{strtod} honours
-the rounding mode, the rounding mode is also supported for input.
+Fortran 2018 (ISO/IEC 1539:2018) is the most recent version
+of the Fortran language standard. GNU Fortran implements some of the
+new features of this standard:
+@itemize @bullet
@item
-@cindex @code{PROTECTED} statement
-@cindex statement, @code{PROTECTED}
-The @code{PROTECTED} statement and attribute.
+All Fortran 2018 features derived from ISO/IEC TS 29113:2012,
+``Further Interoperability of Fortran with C'', are supported by GNU Fortran.
+This includes assumed-type and assumed-rank objects and
+the @code{SELECT RANK} construct as well as the parts relating to
+@code{BIND(C)} functions.
+See also @ref{Further Interoperability of Fortran with C}.
@item
-@cindex @code{VALUE} statement
-@cindex statement, @code{VALUE}
-The @code{VALUE} statement and attribute.
+GNU Fortran supports a subset of features derived from ISO/IEC TS 18508:2015,
+``Additional Parallel Features in Fortran'':
+@itemize @bullet
@item
-@cindex @code{VOLATILE} statement
-@cindex statement, @code{VOLATILE}
-The @code{VOLATILE} statement and attribute.
+The new atomic ADD, CAS, FETCH and ADD/OR/XOR, OR and XOR intrinsics.
@item
-@cindex @code{IMPORT} statement
-@cindex statement, @code{IMPORT}
-The @code{IMPORT} statement, allowing to import
-host-associated derived types.
-
-@item The intrinsic modules @code{ISO_FORTRAN_ENVIRONMENT} is supported,
-which contains parameters of the I/O units, storage sizes. Additionally,
-procedures for C interoperability are available in the @code{ISO_C_BINDING}
-module.
+The @code{CO_MIN} and @code{CO_MAX} and @code{SUM} reduction intrinsics,
+and the @code{CO_BROADCAST} and @code{CO_REDUCE} intrinsic, except that those
+do not support polymorphic types or types with allocatable, pointer or
+polymorphic components.
@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{ISO_C_BINDING}, @code{OMP_LIB} and @code{OMP_LIB_KINDS},
-and @code{OPENACC}.
+Events (@code{EVENT POST}, @code{EVENT WAIT}, @code{EVENT_QUERY}).
@item
-Renaming of operators in the @code{USE} statement.
+Failed images (@code{FAIL IMAGE}, @code{IMAGE_STATUS},
+@code{FAILED_IMAGES}, @code{STOPPED_IMAGES}).
@end itemize
-
-@node Fortran 2008 status
-@subsection 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 compiler supports several of the new features of Fortran 2008;
-the @uref{https://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 Coarray support for serial programs with @option{-fcoarray=single} flag
-and experimental support for multiple images with the @option{-fcoarray=lib}
-flag.
-
-@item Submodules are supported. It should noted that @code{MODULEs} do not
-produce the smod file needed by the descendent @code{SUBMODULEs} unless they
-contain at least one @code{MODULE PROCEDURE} interface. The reason for this is
-that @code{SUBMODULEs} are useless without @code{MODULE PROCEDUREs}. See
-http://j3-fortran.org/doc/meeting/207/15-209.txt for a discussion and a draft
-interpretation. Adopting this interpretation has the advantage that code that
-does not use submodules does not generate smod files.
-
-@item The @code{DO CONCURRENT} construct is supported.
-
-@item The @code{BLOCK} construct is supported.
-
-@item The @code{STOP} and the new @code{ERROR STOP} statements now
-support all constant expressions. Both show the signals which were signaling
-at termination.
-
-@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
-
-
-
-@node Fortran 2018 status
-@subsection Status of Fortran 2018 support
-
-@itemize
-@item ERROR STOP in a PURE procedure
+@item
An @code{ERROR STOP} statement is permitted in a @code{PURE}
procedure.
-@item IMPLICIT NONE with a spec-list
-Support the @code{IMPLICIT NONE} statement with an
+@item
+GNU Fortran supports the @code{IMPLICIT NONE} statement with an
@code{implicit-none-spec-list}.
-@item Behavior of INQUIRE with the RECL= specifier
-
+@item
The behavior of the @code{INQUIRE} statement with the @code{RECL=}
specifier now conforms to Fortran 2018.
@end itemize
-@subsubsection TS 29113 Status (Further Interoperability with C)
-
-GNU Fortran supports some of the new features of the Technical
-Specification (TS) 29113 on Further Interoperability of Fortran with C.
-The @uref{https://gcc.gnu.org/wiki/TS29113Status, wiki} has some information
-about the current TS 29113 implementation status. In particular, the
-following is implemented.
-
-See also @ref{Further Interoperability of Fortran with C}.
-
-@itemize
-@item The @code{OPTIONAL} attribute is allowed for dummy arguments
-of @code{BIND(C) procedures.}
-
-@item The @code{RANK} intrinsic is supported.
-
-@item GNU Fortran's implementation for variables with @code{ASYNCHRONOUS}
-attribute is compatible with TS 29113.
-
-@item Assumed types (@code{TYPE(*)}).
-
-@item Assumed-rank (@code{DIMENSION(..)}).
-
-@item ISO_Fortran_binding (now in Fortran 2018 18.4) is implemented such that
-conversion of the array descriptor for assumed type or assumed rank arrays is
-done in the library. The include file ISO_Fortran_binding.h is can be found in
-@code{~prefix/lib/gcc/$target/$version}.
-@end itemize
-
-
-
-@subsubsection TS 18508 Status (Additional Parallel Features)
-
-GNU Fortran supports the following new features of the Technical
-Specification 18508 on Additional Parallel Features in Fortran:
-
-@itemize
-@item The new atomic ADD, CAS, FETCH and ADD/OR/XOR, OR and XOR intrinsics.
-
-@item The @code{CO_MIN} and @code{CO_MAX} and @code{SUM} reduction intrinsics.
-And the @code{CO_BROADCAST} and @code{CO_REDUCE} intrinsic, except that those
-do not support polymorphic types or types with allocatable, pointer or
-polymorphic components.
-
-@item Events (@code{EVENT POST}, @code{EVENT WAIT}, @code{EVENT_QUERY})
-
-@item Failed images (@code{FAIL IMAGE}, @code{IMAGE_STATUS},
-@code{FAILED_IMAGES}, @code{STOPPED_IMAGES})
-
-@end itemize
-
-
-
-
@c =====================================================================
@c PART I: INVOCATION REFERENCE
@c =====================================================================
@@ -570,10 +570,46 @@ Enhance test coverage by forcing most forall assignments to use temporary.
@cindex preprocessor
@cindex options, preprocessor
@cindex CPP
-
-Preprocessor related options. See section
-@ref{Preprocessing and conditional compilation} for more detailed
-information on preprocessing in @command{gfortran}.
+@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. The macros @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.
+
+GNU Fortran supports a number of @code{INTEGER} and @code{REAL} kind types
+in additional to the kind types required by the Fortran standard.
+The availability of any given kind type is architecture dependent. The
+following pre-defined preprocessor macros can be used to conditionally
+include code for these additional kind types: @code{__GFC_INT_1__},
+@code{__GFC_INT_2__}, @code{__GFC_INT_8__}, @code{__GFC_INT_16__},
+@code{__GFC_REAL_10__}, and @code{__GFC_REAL_16__}.
+
+While CPP is the de-facto standard for preprocessing Fortran code,
+Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
+Conditional Compilation, which is not widely used and not directly
+supported by the GNU Fortran compiler. You can use the program coco
+to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}).
+
+The following options control preprocessing of Fortran code:
@table @gcctabopt
@item -cpp