fopen(3) - NetBSD Manual Pages

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


NAME

     fopen, fdopen, freopen - stream open functions


LIBRARY

     Standard C Library (libc, -lc)


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''   Open text file for reading.

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

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

     ``w+''  Open for reading and writing.  The file is created if it does not
             exist, otherwise it is truncated.

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

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

     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)).

     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 reposi-
     tioning 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 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.

     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'').

NetBSD 1.4                       June 4, 1993                                2