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

NAME
     fopen, fdopen, freopen -- 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);

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
     sequences (Additional characters may follow these sequences.):

     ``r''   Open text file for	reading.  The stream is	positioned at the
	     beginning of the file.

     ``r+''  Open for reading and writing.  The	stream is positioned at	the
	     beginning of the file.

     ``w''   Truncate to zero length or	create text file for writing.  The
	     stream is positioned at the beginning of the file.

     ``w+''  Open for reading and writing.  The	file is	created	if it does not
	     exist, otherwise it is truncated.	The stream is positioned at
	     the beginning of the file.

     ``a''   Open for writing.	The file is created if it does not exist.  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.

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

     The mode string can also include the letter ``b'' either as last charac-
     ter or as a character between the characters in any of the	two-character
     strings described above.  This is strictly	for compatibility with ISO/IEC
     9899:1990 (``ISO C90'') and has no	effect;	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.  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:

	   +o   Streams originally opened with mode ``r'' can only be reopened
	       with that same mode.

	   +o   Streams originally opened with mode ``a'' can be	reopened with
	       the same	mode, or mode ``w''.

	   +o   Streams originally opened with mode ``w'' can be	reopened with
	       the same	mode, or mode ``a''.

	   +o   Streams originally opened with mode ``r+'', ``w+'', or ``a+''
	       can be reopened with any	mode.

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

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(),	or freopen()
			was invalid.

     The fopen(), fdopen() and freopen() 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'').  The fdopen() function conforms to IEEE Std	1003.1-1988
     (``POSIX.1'').

FreeBSD	9.2		       January 26, 2003			   FreeBSD 9.2

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

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