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FOPEN(3)		 BSD 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
     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	read-
     ing 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 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.  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 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).

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"), 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").

BSD			       October 17, 2011				   BSD

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

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