\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.
* GFORTRAN_STDOUT_UNIT:: Unit number for standard output
* GFORTRAN_STDERR_UNIT:: Unit number for 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
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
@menu
* Fortran 2003 status::
* Fortran 2008 status::
-* TR 29113 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
@code{ISO_C_BINDINGS} and @code{COMPILER_VERSION} and @code{COMPILER_OPTIONS}
of @code{ISO_FORTRAN_ENV}.
-@item Experimental coarray, use the @option{-fcoarray=single} or
-@option{-fcoarray=lib} 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 TR 29113 status
-@section Fortran 29113 status
+@node TS 29113 status
+@section Technical Specification 29113 Status
-GNU Fortran supports some of the new features of the technical report (TR)
-29113 on Further Interoperability of Fortran with C.
-@uref{http://gcc.gnu.org/wiki/Fortran2008Status, wiki} has some information
-about the current TR 29113 implementation status. In particular, the
+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=f2008} option.
-@item The OPTIONAL attribute is now allowed for dummy arguments of
-BIND(C) procedures.
+@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
* 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 ---------------------------------------------------------------------
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 suppports this type. If
+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
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.
@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),
-@code{GFC_STD_F2008_OBS} (256) and GFC_STD_F2008_TR (512). Default:
+@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_TR | GFC_STD_F2008_OBS | GFC_STD_F77
+| 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}.
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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