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FOPEN(3)		   Linux Programmer's Manual		      FOPEN(3)

NAME
       fopen, fdopen, freopen -	stream open functions

SYNOPSIS
       #include	<stdio.h>

       FILE *fopen(const char *path, const char	*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  follow-
       ing sequences (Additional characters may	follow these sequences.):

       r      Open text	file for reading.  The stream is positioned at the be-
	      ginning of the file.

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

       w      Truncate	file  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 appending (writing at end of file).  The	file  is  cre-
	      ated  if it does not exist.  The stream is positioned at the end
	      of the file.

       a+     Open for reading and appending (writing at end  of  file).   The
	      file  is created if it does not exist.  The stream is positioned
	      at the end of the	file.

       The mode	string can also	include	the letter  ``b''  either  as  a  last
       character  or  as a character between the characters in any of the two-
       character strings described above.  This	is strictly for	 compatibility
       with  ANSI X3.159-1989 (``ANSI C'') and has no effect; the ``b''	is ig-
       nored on	all POSIX conforming systems, including	Linux.	(Other systems
       may treat text files and	binary files differently, and adding the ``b''
       may be a	good idea if you do I/O	to a binary file and expect that  your
       program may be ported to	non-Unix environments.)

       Any   created   files   will  have  mode	 S_IRUSR|S_IWUSR|S_IRGRP|S_IW-
       GRP|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.
       Note that ANSI C	requires that a	file  positioning  function  intervene
       between	output and input, unless an input operation encounters end-of-
       file.  (If this condition is not	met, then a read is allowed to	return
       the result of writes other than the most	recent.)  Therefore it is good
       practice	(and indeed sometimes necessary	under Linux) to	put  an	 fseek
       or  fgetpos  operation  between	write  and  read  operations on	such a
       stream.	This operation may be an apparent no-op	(as in fseek(...,  0L,
       SEEK_CUR) called	for its	synchronizing side effect.

       Opening a file in append	mode (a	as the first character of mode)	causes
       all subsequent write operations to this stream to occur at end-of-file,
       as if preceded by an
	      fseek(stream,0,SEEK_END);
       call.

       The fdopen function associates a	stream with the	existing file descrip-
       tor, fildes.  The mode of the stream (one of the	values "r", "r+", "w",
       "w+",  "a", "a+") must be compatible with the mode of the file descrip-
       tor.  The file position indicator of the	new stream is set to that  be-
       longing	to  fildes,  and  the  error  and  end-of-file	indicators are
       cleared.	 Modes "w" or "w+" do not cause	truncation of the  file.   The
       file  descriptor	is not dup'ed, and will	be closed when the stream cre-
       ated by fdopen is closed.  The result of	applying fdopen	 to  a	shared
       memory object is	undefined.

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

RETURN VALUE
       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 provided	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).

CONFORMING TO
       The fopen and freopen functions conform	to  ANSI  X3.159-1989  (``ANSI
       C'').	The   fdopen   function	  conforms   to	  IEEE	Std1003.1-1988
       (``POSIX.1'').

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

BSD MANPAGE			  2002-01-03			      FOPEN(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO

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