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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.	Truncate the file to zero length if it exists or cre-
	     ate 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	read-
     ing and writing.  An optional "x" following "w" or	"w+" causes the
     fopen() call to fail if the file already exists.  An optional "e" follow-
     ing the above causes the fopen() call to set the FD_CLOEXEC flag on the
     underlying	file descriptor.

     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 "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.  If the "e" mode
     option is present,	the FD_CLOEXEC flag is set, otherwise it remains un-
     changed.  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 as-
     sociated 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 meaningful
     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).

     The fmemopen() function may also fail and set errno if the	size argument
     is	0.

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 "e" mode	option does not	conform	to any
     standard but is also supported by glibc.  The fmemopen() function con-
     forms to IEEE Std 1003.1-2008 ("POSIX.1").	 The "b" mode does not conform
     to	any standard but is also supported by glibc.

FreeBSD	13.0		       January 30, 2013			  FreeBSD 13.0

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

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