Mac OS X Manual Page For fopen(3) (original) (raw)

FOPEN(3) BSD Library Functions Manual FOPEN(3)

NAME fdopen, fopen, freopen -- stream open functions

LIBRARY Standard C Library (libc, -lc)

SYNOPSIS #include <stdio.h>

 FILE *
 **fdopen**(int fildes, const char *mode);

 FILE *
 **fopen**(const char *restrict filename, const char *restrict mode);

 FILE *
 **freopen**(const char *restrict filename, const char *restrict mode,
     FILE *restrict stream);

DESCRIPTION The fopen() function opens the file whose name is the string pointed to by filename 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 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 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)](fseek.3.html#//apple%5Fref/doc/man/3/fseek) 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 Subsequent
         quent writes to the file will always end up at the then current
         end of file, irrespective of any intervening [fseek(3)](fseek.3.html#//apple%5Fref/doc/man/3/fseek) or similar.

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

 Finally, as an extension to the standards (and thus may not be portable),
 mode string may end with the letter ``x'', which insists on creating a
 new file when used with ``w'' or ``a''.  If path exists, then an error is
 returned (this is the equivalent of specifying O_EXCL with [open(2)](../man2/open.2.html#//apple%5Fref/doc/man/2/open)).

 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)](../man2/umask.2.html#//apple%5Fref/doc/man/2/umask)).

 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, descriptor,
 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)](fclose.3.html#//apple%5Fref/doc/man/3/fclose), fildes is
 closed also.

 The **freopen**() function opens the file whose name is the string pointed to
 by filename 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 filename 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:

       **oo**   Streams originally opened with mode ``r'' can only be reopened
           with that same mode.

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

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

       **oo**   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 associated
 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)](malloc.3.html#//apple%5Fref/doc/man/3/malloc).

 The **fopen**() function may also fail and set errno for any of the errors
 specified for the routine [open(2)](../man2/open.2.html#//apple%5Fref/doc/man/2/open).

 The **fdopen**() function may also fail and set errno for any of the errors
 specified for the routine [fcntl(2)](../man2/fcntl.2.html#//apple%5Fref/doc/man/2/fcntl).

 The **freopen**() function may also fail and set errno for any of the errors
 specified for the routines [open(2)](../man2/open.2.html#//apple%5Fref/doc/man/2/open), [fclose(3)](fclose.3.html#//apple%5Fref/doc/man/3/fclose) and [fflush(3)](fflush.3.html#//apple%5Fref/doc/man/3/fflush).

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'').

BSD January 26, 2003 BSD