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FOPEN(3)	       FreeBSD Library Functions Manual		      FOPEN(3)

NAME
     fopen, fdopen, freopen, fmemopen -- stream	open functions

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <stdio.h>

     FILE *
     fopen(const char *	restrict path, const char * restrict mode);

     FILE *
     fdopen(int	fildes,	const char *mode);

     FILE *
     freopen(const char	*path, const char *mode, FILE *stream);

     FILE *
     fmemopen(void *restrict *buf, size_t size,	const char * restrict mode);

DESCRIPTION
     The fopen() function opens	the file whose name is the string pointed to
     by	path and associates a stream with it.

     The argument mode points to a string beginning with one of	the following
     letters:

     ``r''   Open for reading.	The stream is positioned at the	beginning of
	     the file.	Fail if	the file does not exist.

     ``w''   Open for writing.	The stream is positioned at the	beginning of
	     the file.	Create the file	if it does not exist.

     ``a''   Open for writing.	The stream is positioned at the	end of the
	     file.  Subsequent writes to the file will always end up at	the
	     then current end of file, irrespective of any intervening
	     fseek(3) or similar.  Create the file if it does not exist.

     An	optional ``+'' following ``r'',	``w'', or ``a''	opens the file for
     both reading and writing.	An optional ``x'' following ``w'' or ``w+''
     causes the	fopen()	call to	fail if	the file already exists.

     The mode string can also include the letter ``b'' after either the	``+''
     or	the first letter.  This	is strictly for	compatibility with ISO/IEC
     9899:1990 (``ISO C90'') and has effect only for fmemopen()	; otherwise
     the ``b'' is ignored.

     Any created files will have mode ``S_IRUSR	| S_IWUSR | S_IRGRP | S_IWGRP
     | S_IROTH | S_IWOTH'' (0666), as modified by the process' umask value
     (see umask(2)).

     Reads and writes may be intermixed	on read/write streams in any order,
     and do not	require	an intermediate	seek as	in previous versions of	stdio.
     This is not portable to other systems, however; ANSI C requires that a
     file positioning function intervene between output	and input, unless an
     input operation encounters	end-of-file.

     The fdopen() function associates a	stream with the	existing file descrip-
     tor, fildes.  The mode of the stream must be compatible with the mode of
     the file descriptor.  The ``x'' mode option is ignored.  When the stream
     is	closed via fclose(3), fildes is	closed also.

     The freopen() function opens the file whose name is the string pointed to
     by	path and associates the	stream pointed to by stream with it.  The
     original stream (if it exists) is closed.	The mode argument is used just
     as	in the fopen() function.

     If	the path argument is NULL, freopen() attempts to re-open the file
     associated	with stream with a new mode.  The new mode must	be compatible
     with the mode that	the stream was originally opened with: Streams open
     for reading can only be re-opened for reading, streams open for writing
     can only be re-opened for writing,	and streams open for reading and writ-
     ing can be	re-opened in any mode.	The ``x'' mode option is not meaning-
     ful in this context.

     The primary use of	the freopen() function is to change the	file associ-
     ated with a standard text stream (stderr, stdin, or stdout).

     The fmemopen() function associates	the buffer given by the	buf and	size
     arguments with a stream.  The buf argument	is either a null pointer or
     point to a	buffer that is at least	size bytes long.  If a null pointer is
     specified as the buf argument, fmemopen() allocates size bytes of memory.
     This buffer is automatically freed	when the stream	is closed. Buffers can
     be	opened in text-mode (default) or binary-mode (if ``b'' is present in
     the second	or third position of the mode argument). Buffers opened	in
     text-mode make sure that writes are terminated with a NULL	byte, if the
     last write	hasn't filled up the whole buffer. Buffers opened in binary-
     mode never	append a NULL byte.

RETURN VALUES
     Upon successful completion	fopen(), fdopen() and freopen()	return a FILE
     pointer.  Otherwise, NULL is returned and the global variable errno is
     set to indicate the error.

ERRORS
     [EINVAL]		The mode argument to fopen(), fdopen(),	freopen(), or
			fmemopen() was invalid.

     The fopen(), fdopen(), freopen() and fmemopen() functions may also	fail
     and set errno for any of the errors specified for the routine malloc(3).

     The fopen() function may also fail	and set	errno for any of the errors
     specified for the routine open(2).

     The fdopen() function may also fail and set errno for any of the errors
     specified for the routine fcntl(2).

     The freopen() function may	also fail and set errno	for any	of the errors
     specified for the routines	open(2), fclose(3) and fflush(3).

SEE ALSO
     open(2), fclose(3), fileno(3), fseek(3), funopen(3)

STANDARDS
     The fopen() and freopen() functions conform to ISO/IEC 9899:1990
     (``ISO C90''), with the exception of the ``x'' mode option	which conforms
     to	ISO/IEC	9899:2011 (``ISO C11'').  The fdopen() function	conforms to
     IEEE Std 1003.1-1988 (``POSIX.1'').  The fmemopen() function conforms to
     IEEE Std 1003.1-2008 (``POSIX.1'').  The ``b'' mode does not conform to
     any standard but is also supported	by glibc.

FreeBSD	9.3		       January 30, 2013			   FreeBSD 9.3

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS

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