fdopen(3) - NetBSD Manual Pages

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FOPEN(3)                NetBSD 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 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 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.

     The mode string can also include the letter ``b'' either as a last 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
     ANSI X3.159-1989 (``ANSI C89'') and has no effect; the ``b'' is ignored.

     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.

     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.

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

     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'').  The fdopen() function conforms to ISO/IEC 9945-1:1990
     (``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);
             }

NetBSD 3.0                       June 4, 1993                       NetBSD 3.0