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NetBSD 6.1.5 - man page for fdopen (netbsd section 3)

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 * restrict path, const char * restrict mode, FILE * restrict stream);

DESCRIPTION
     The fopen() function opens the file whose name is the string pointed to by path and asso-
     ciates a stream with it.

     The argument mode points to a string beginning with one of the following sequences (Addi-
     tional characters may follow these sequences.):

     ``r''   Open for reading.

     ``r+''  Open for reading and writing.

     ``w''   Open for writing.	Truncate file to zero length or create file.

     ``w+''  Open for reading and writing.  Truncate file to zero length or create file.

     ``a''   Append; open for writing.	The file is created if it does not exist.

     ``a+''  Append; open for reading and writing.  The file is created if it does not exist.

     Additionally:

       o   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 C89'') and has no
	   effect; the ``b'' is ignored.

       o   The letter ``f'' in the mode string restricts fopen() to regular files; if the file
	   opened is not a regular file, fopen() will fail.  This is a non ANSI X3.159-1989
	   (``ANSI C89'') extension.

       o   The letter ``e'' in the mode string sets the close-on-exec flag in the file descrip-
	   tors of the newly opened file files; if the operation fails, fopen() will fail.  This
	   is a non ANSI X3.159-1989 (``ANSI C89'') extension.

       o   The letter 'x' in the mode turns on exclusive open mode to the file ( O_EXCL) which
	   means that the file will not be created if it already exists.

     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(2) value.

     Opening a file with append mode causes all subsequent writes to it to be forced to the then
     current end of file, regardless of intervening repositioning of the stream.

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

     The fdopen() function associates a stream with the existing file descriptor, 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.

     The freopen() function opens the file whose name is the string pointed to by path and asso-
     ciates 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 VALUES
     Upon successful completion fopen(), fdopen() and freopen() return a FILE pointer.	Other-
     wise, NULL is returned and the global variable errno is set to indicate the error.

ERRORS
     The functions may fail if:

     [EFTYPE]		The file is not a regular file and the character ``f'' is specified in
			the mode.

     [EINVAL]		The specified mode 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 ANSI X3.159-1989 (``ANSI C89'').  All three
     functions are specified in IEEE Std 1003.1-2008 (``POSIX.1'').

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);
	     }

BSD					November 14, 2012				      BSD


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