MirOS Manual: fdopen(3), fopen(3), freopen(3)

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

NAME

     fopen, fdopen, freopen - stream open functions

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 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"     Open for writing. The file is created if it does not exist.

     "a+"    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-
     character strings described above. This is strictly for compatibility
     with ANSI X3.159-1989 ("ANSI C") and has no effect; the ``b'' is ignored.

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

     Opening a file in append mode causes all subsequent writes to it to be
     forced to the current end-of-file, regardless of intervening reposition-
     ing of the stream.

     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 cannot be arbitrarily intermixed on read/write streams.
     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 stream is positioned at the file offset of the
     file descriptor. If fdopen() fails, the file descriptor fildes is not af-
     fected in any way.

     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 ori-
     ginal stream (if it exists) is always closed, even if freopen() fails.
     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 Std 1003.1-1988 ("POSIX").

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);
             }

MirOS BSD #10-current            June 4, 1993                                1

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