\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename gfortran.info
-@set copyrights-gfortran 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
+@set copyrights-gfortran 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
@include gcc-common.texi
The GNU Fortran compiler front end was
designed initially as a free replacement for,
or alternative to, the unix @command{f95} command;
-@command{gfortran} is the command you'll use to invoke the compiler.
+@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.
@dfn{machine code},
code designed to be efficiently translated and processed
by a machine such as your computer.
-Humans usually aren't as good writing machine code
+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.
@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/}).
+(version 3.1, @url{http://openmp.org/@/wp/@/openmp-specifications/}).
@node Varying Length Character Strings
@subsection Varying Length Character Strings
* GFORTRAN_STDIN_UNIT:: Unit number for standard input
* GFORTRAN_STDOUT_UNIT:: Unit number for standard output
* GFORTRAN_STDERR_UNIT:: Unit number for standard error
-* GFORTRAN_USE_STDERR:: Send library output to standard error
* GFORTRAN_TMPDIR:: Directory for scratch files
-* GFORTRAN_UNBUFFERED_ALL:: Don't buffer I/O for all units.
-* GFORTRAN_UNBUFFERED_PRECONNECTED:: Don't buffer I/O for preconnected units.
+* GFORTRAN_UNBUFFERED_ALL:: Do not buffer I/O for all units.
+* GFORTRAN_UNBUFFERED_PRECONNECTED:: Do not buffer I/O for preconnected units.
* GFORTRAN_SHOW_LOCUS:: Show location for runtime errors
* GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted
* GFORTRAN_DEFAULT_RECL:: Default record length for new files
* GFORTRAN_LIST_SEPARATOR:: Separator for list output
* GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O
-* GFORTRAN_ERROR_DUMPCORE:: Dump core on run-time errors
* GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors
@end menu
preconnected to standard error. This must be a positive integer.
The default value is 0.
-@node GFORTRAN_USE_STDERR
-@section @env{GFORTRAN_USE_STDERR}---Send library output to standard error
-
-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
-@samp{0}, standard output is used.
-
@node GFORTRAN_TMPDIR
@section @env{GFORTRAN_TMPDIR}---Directory for scratch files
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
+@section @env{GFORTRAN_UNBUFFERED_ALL}---Do not buffer I/O on all units
This environment variable controls whether all I/O is unbuffered. If
the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is
This is the default.
@node GFORTRAN_UNBUFFERED_PRECONNECTED
-@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Don't buffer I/O on preconnected units
+@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Do not buffer I/O on preconnected units
The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls
whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered. If
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
+@samp{n}, @samp{N} or @samp{0}, do not print filename and line numbers
for runtime errors. The default is to print the location.
@node GFORTRAN_OPTIONAL_PLUS
open statement}. This is to give control over data formats to
users who do not have the source code of their program available.
-@node GFORTRAN_ERROR_DUMPCORE
-@section @env{GFORTRAN_ERROR_DUMPCORE}---Dump core on run-time errors
-
-If the @env{GFORTRAN_ERROR_DUMPCORE} variable is set to
-@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
-then library run-time errors cause core dumps. To disable the core
-dumps, set the variable to @samp{n}, @samp{N}, @samp{0}. Default
-is not to core dump unless the @option{-fdump-core} compile option
-was used.
-
@node GFORTRAN_ERROR_BACKTRACE
@section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors
-If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to
-@samp{y}, @samp{Y} or @samp{1} (only the first letter is relevant)
-then a backtrace is printed when a run-time error occurs.
-To disable the backtracing, set the variable to
-@samp{n}, @samp{N}, @samp{0}. Default is not to print a backtrace
-unless the @option{-fbacktrace} compile option
-was used.
+If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to @samp{y},
+@samp{Y} or @samp{1} (only the first letter is relevant) then a
+backtrace is printed when a serious run-time error occurs. To disable
+the backtracing, set the variable to @samp{n}, @samp{N}, @samp{0}.
+Default is to print a backtrace unless the @option{-fno-backtrace}
+compile option was used.
@c =====================================================================
@c PART II: LANGUAGE REFERENCE
@menu
* Fortran 2003 status::
* Fortran 2008 status::
+* TS 29113 status::
@end menu
@node Fortran 2003 status
@item Polymorphic entities (``@code{CLASS}'') for derived types -- including
@code{SAME_TYPE_AS}, @code{EXTENDS_TYPE_OF} and @code{SELECT TYPE}.
-Note that the support for array-valued polymorphic entities is incomplete
-and unlimited polymophism is currently not supported.
+Note that unlimited polymorphism is currently not supported.
+
+@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 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
+@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
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
+The GNU Fortran compiler 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.
@code{ISO_C_BINDINGS} and @code{COMPILER_VERSION} and @code{COMPILER_OPTIONS}
of @code{ISO_FORTRAN_ENV}.
-@item Experimental coarray support (for one image only), use the
-@option{-fcoarray=single} flag to enable it.
+@item Coarray support for serial programs with @option{-fcoarray=single} flag
+and experimental support for multiple images with the @option{-fcoarray=lib}
+flag.
+
+@item The @code{DO CONCURRENT} construct is supported.
@item The @code{BLOCK} construct is supported.
+@node TS 29113 status
+@section Technical Specification 29113 Status
+
+GNU Fortran supports some of the new features of the Technical
+Specification (TS) 29113 on Further Interoperability of Fortran with C.
+The @uref{http://gcc.gnu.org/wiki/TS29113Status, wiki} has some information
+about the current TS 29113 implementation status. In particular, the
+following is implemented.
+
+@itemize
+@item The @option{-std=f2008ts} option.
+
+@item The @code{OPTIONAL} attribute is allowed for dummy arguments
+of @code{BIND(C) procedures.}
+
+@item The RANK intrinsic is supported.
+
+@item GNU Fortran's implementation for variables with @code{ASYNCHRONOUS}
+attribute is compatible with TS 29113.
+@end itemize
+
+
+
@c ---------------------------------------------------------------------
@c Compiler Characteristics
@c ---------------------------------------------------------------------
* KIND Type Parameters::
* Internal representation of LOGICAL variables::
* Thread-safety of the runtime library::
+* Data consistency and durability::
@end menu
further functionality might not be thread-safe. For details, please
consult the documentation for your operating system.
+
+@node Data consistency and durability
+@section Data consistency and durability
+@cindex consistency, durability
+
+This section contains a brief overview of data and metadata
+consistency and durability issues when doing I/O.
+
+With respect to durability, GNU Fortran makes no effort to ensure that
+data is committed to stable storage. If this is required, the GNU
+Fortran programmer can use the intrinsic @code{FNUM} to retrieve the
+low level file descriptor corresponding to an open Fortran unit. Then,
+using e.g. the @code{ISO_C_BINDING} feature, one can call the
+underlying system call to flush dirty data to stable storage, such as
+@code{fsync} on POSIX, @code{_commit} on MingW, or @code{fcntl(fd,
+F_FULLSYNC, 0)} on Mac OS X. The following example shows how to call
+fsync:
+
+@smallexample
+ ! Declare the interface for POSIX fsync function
+ interface
+ function fsync (fd) bind(c,name="fsync")
+ use iso_c_binding, only: c_int
+ integer(c_int), value :: fd
+ integer(c_int) :: fsync
+ end function fsync
+ end interface
+
+ ! Variable declaration
+ integer :: ret
+
+ ! Opening unit 10
+ open (10,file="foo")
+
+ ! ...
+ ! Perform I/O on unit 10
+ ! ...
+
+ ! Flush and sync
+ flush(10)
+ ret = fsync(fnum(10))
+
+ ! Handle possible error
+ if (ret /= 0) stop "Error calling FSYNC"
+@end smallexample
+
+With respect to consistency, for regular files GNU Fortran uses
+buffered I/O in order to improve performance. This buffer is flushed
+automatically when full and in some other situations, e.g. when
+closing a unit. It can also be explicitly flushed with the
+@code{FLUSH} statement. Also, the buffering can be turned off with the
+@code{GFORTRAN_UNBUFFERED_ALL} and
+@code{GFORTRAN_UNBUFFERED_PRECONNECTED} environment variables. Special
+files, such as terminals and pipes, are always unbuffered. Sometimes,
+however, further things may need to be done in order to allow other
+processes to see data that GNU Fortran has written, as follows.
+
+The Windows platform supports a relaxed metadata consistency model,
+where file metadata is written to the directory lazily. This means
+that, for instance, the @code{dir} command can show a stale size for a
+file. One can force a directory metadata update by closing the unit,
+or by calling @code{_commit} on the file descriptor. Note, though,
+that @code{_commit} will force all dirty data to stable storage, which
+is often a very slow operation.
+
+The Network File System (NFS) implements a relaxed consistency model
+called open-to-close consistency. Closing a file forces dirty data and
+metadata to be flushed to the server, and opening a file forces the
+client to contact the server in order to revalidate cached
+data. @code{fsync} will also force a flush of dirty data and metadata
+to the server. Similar to @code{open} and @code{close}, acquiring and
+releasing @code{fcntl} file locks, if the server supports them, will
+also force cache validation and flushing dirty data and metadata.
+
+
@c ---------------------------------------------------------------------
@c Extensions
@c ---------------------------------------------------------------------
* Missing period in FORMAT specifications::
* I/O item lists::
* BOZ literal constants::
+* @code{Q} exponent-letter::
* Real array indices::
* Unary operators::
* Implicitly convert LOGICAL and INTEGER values::
of the @code{READ} statement, and the output item lists of the
@code{WRITE} and @code{PRINT} statements, to start with a comma.
+@node @code{Q} exponent-letter
+@subsection @code{Q} exponent-letter
+@cindex @code{Q} exponent-letter
+
+GNU Fortran accepts real literal constants with an exponent-letter
+of @code{Q}, for example, @code{1.23Q45}. The constant is interpreted
+as a @code{REAL(16)} entity on targets that support this type. If
+the target does not support @code{REAL(16)} but has a @code{REAL(10)}
+type, then the real-literal-constant will be interpreted as a
+@code{REAL(10)} entity. In the absence of @code{REAL(16)} and
+@code{REAL(10)}, an error will occur.
+
@node BOZ literal constants
@subsection BOZ literal constants
@cindex BOZ literal constants
and environment variables that influence run-time behavior.
GNU Fortran strives to be compatible to the
-@uref{http://www.openmp.org/mp-documents/spec30.pdf,
-OpenMP Application Program Interface v3.0}.
+@uref{http://www.openmp.org/mp-documents/spec31.pdf,
+OpenMP Application Program Interface v3.1}.
To enable the processing of the OpenMP directive @code{!$omp} in
free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp}
store_catalog(7)%description = "milk bottle"
store_catalog(7)%price = 1.2
-! Assignments of a whole variable don't change
+! Assignments of a whole variable do not change
store_catalog(12) = pear
print *, store_catalog(12)
@end example
@cindex @code{ENCODE}
@cindex @code{DECODE}
-GNU Fortran doesn't support the @code{ENCODE} and @code{DECODE}
+GNU Fortran does not support the @code{ENCODE} and @code{DECODE}
statements. These statements are best replaced by @code{READ} and
@code{WRITE} statements involving internal files (@code{CHARACTER}
variables and arrays), which have been part of the Fortran standard since
@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
+Let us consider two examples of actually passing a procedure pointer from
C to Fortran and vice versa. Note that these examples are also very
-similar to passing ordinary pointers between both languages.
-First, consider this code in C:
+similar to passing ordinary pointers between both languages. First,
+consider this code in C:
@smallexample
/* Procedure implemented in Fortran. */
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
+a Technical Specification (TS 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.
+GNU Fortran already supports the C-interoperable @code{OPTIONAL}
+attribute; for absent arguments, a @code{NULL} pointer is passed.
@node GNU Fortran Compiler Directives
@section GNU Fortran Compiler Directives
-The Fortran standard standard describes how a conforming program shall
+The Fortran standard describes how a conforming program shall
behave; however, the exact implementation is not standardized. In order
to allow the user to choose specific implementation details, compiler
directives can be used to set attributes of variables and procedures
@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
+standard to be used, whether backtracing should be enabled
and whether range checks should be performed. The syntax allows for
upward compatibility since the number of passed flags is specified; for
non-passed flags, the default value is used. See also
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}.
+@code{GFC_STD_LEGACY} (64), @code{GFC_STD_F2008} (128),
+@code{GFC_STD_F2008_OBS} (256) and GFC_STD_F2008_TS (512). Default:
+@code{GFC_STD_F95_OBS | GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003
+| GFC_STD_F2008 | GFC_STD_F2008_TS | GFC_STD_F2008_OBS | GFC_STD_F77
+| GFC_STD_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}[3] @tab Unused.
@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
@item @emph{Example}:
@smallexample
- /* Use gfortran 4.5 default options. */
- static int options[] = @{68, 255, 0, 0, 0, 1, 0, 1@};
+ /* Use gfortran 4.7 default options. */
+ static int options[] = @{68, 511, 0, 0, 1, 1, 0, 1@};
_gfortran_set_options (8, &options);
@end smallexample
@end table
@node _gfortran_set_fpe
-@subsection @code{_gfortran_set_fpe} --- Set when a Floating Point Exception should be raised
+@subsection @code{_gfortran_set_fpe} --- Enable floating point exception traps
@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.
+@code{_gfortran_set_fpe} enables floating point exception traps for
+the specified exceptions. On most systems, this will result in a
+SIGFPE signal being sent and the program being aborted.
@item @emph{Syntax}:
@code{void _gfortran_set_fpe (int val)}
(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).
+@code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_INEXACT} (32).
@end multitable
@item @emph{Example}:
happening on GNU Fortran,
but others are ``mainstream'' projects in need of enthusiastic hackers.
All of these projects are important!
-We'll eventually get around to the things here,
+We will eventually get around to the things here,
but they are also things doable by someone who is willing and able.
@menu
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