fdopen(3) - NetBSD Manual Pages

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


NAME

     fopen, fdopen, freopen - stream open functions


SYNOPSIS

     #include <stdio.h>

     FILE *
     fopen(char *path, char *mode);

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

     FILE *
     freopen(char *path, 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''   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 writing.  The file is created if it does not exist.  The
             stream is positioned at the end of the file.

     ``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.

     The mode string can also include the letter ``b'' either as a third char-
     acter or as a character between the characters in any of the two-charac-
     ter strings described above.  This is strictly for compatibility with AN-
     SI X3.159-1989 (``ANSI C'') 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 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 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
     C''). The fdopen() function conforms to IEEE Std1003.1-1990 (``POSIX'').

4.4BSD                           June 4, 1993                                2