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FOPEN(3)	       FreeBSD Library Functions 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 following
     sequences (additional characters may follow these sequences):

     "r" or "rb"
	     Open file for reading.

     "r+" or "rb+" or "r+b"
	     Open for reading and writing.

     "w" or "wb"
	     Open for writing.	The file is created if it does not exist, oth-
	     erwise it is truncated.

     "w+" or "wb+" or "w+b"
	     Open for reading and writing.  The	file is	created	if it does not
	     exist, otherwise it is truncated.

     "a" or "ab"
	     Open for writing.	The file is created if it does not exist.

     "a+" or "ab+" or "a+b"
	     Open for reading and writing.  The	file is	created	if it does not
	     exist.

     The letter	"b" in the mode	strings	above is strictly for compatibility
     with ANSI X3.159-1989 ("ANSI C89")	and has	no effect; the "b" is ignored.

     After any of the above prefixes, the mode string can also include zero or
     more of the following:

     "e"     The close-on-exec flag is set on the underlying file descriptor
	     of	the new	FILE.

     "x"     If	the mode string	starts with "w"	or "a" then the	function shall
	     fail if the file specified	by path	already	exists,	as if the
	     O_EXCL flag was passed to the open(2) function.  It has no	effect
	     if	used with fdopen() or the mode string begins with "r".

     The fopen() and freopen() functions initially position the	stream at the
     start of the file unless the file is opened in append mode	(`a' or	`a+'),
     in	which case the stream is initially positioned at the end of the	file.

     Opening a file in append mode causes all subsequent writes	to it to be
     forced to the current end-of-file,	regardless of intervening reposition-
     ing of the	stream.

     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 cannot be	arbitrarily intermixed on read/write streams.
     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 stream is positioned at the file	offset of the
     file descriptor.  If fdopen() fails, the file descriptor fildes is	not
     affected in any way.

     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 always closed, even if freopen()	fails.
     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 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 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).

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

STANDARDS
     The fopen() and freopen() functions conform to ANSI X3.159-1989
     ("ANSI C89").  The	fdopen() function conforms to IEEE Std 1003.1-1988
     ("POSIX.1").

HISTORY
     The fopen() function first	appeared in Version 1 AT&T UNIX.  The fdopen()
     and freopen() functions first appeared in Version 7 AT&T UNIX.

     Opening a file for	both reading and writing has been possible since 2BSD.

     Support for the "e" and "x" mode letters appeared in OpenBSD 5.7.

AUTHORS
     Dennis Ritchie originally implemented fopen() in PDP-11 assembler.
     Keith Sklower first implemented read-write	access.

CAVEATS
     Proper code using fdopen()	with error checking should close(2) fildes in
     case of failure, and fclose(3) the	resulting FILE * in case of success.

	     FILE *file;
	     int fd;

	     if	((file = fdopen(fd, "r")) != NULL) {
		     /*	perform	operations on the FILE * */
		     fclose(file);
	     } else {
		     /*	failure, report	the error */
		     close(fd);
	     }

FreeBSD	13.0		       January 15, 2015			  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY | AUTHORS | CAVEATS

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