\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
@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
* 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. */
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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