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 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.

    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 character or as a character between the characters in any of the two-character strings described above. If the ``b'' is not specified, then the file is assumed to contain text. On input, carrige returns (``\r'') will be translated into line feeds (``\n''). The reverse translation will occur on output. If the ``b'' is specified, no such translation will occur.

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)).

The fdopen function associates a stream with the existing file descriptor, fildes The mode of the stream must be compatible with the mode of the file descriptor. See the section on BUGS.

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) or stat(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).

BUGS
If fdopen is passed a file descriptor in use by another stdio stream (such as that available from the fileno macro), the result is currently undefined. If you need to do such an operation, you should dup(2) the result of the fileno macro before passing it to fdopen.

Access bits are not currently checked for any file descriptor passed to fdopen which is a character-special file.

SEE ALSO
open(2), stat(2), fclose(3), fseek(3), funopen(3)

STANDARDS
The fopen and freopen functions conform to ANSI/C. The fdopen function conforms to POSIX 1003.1 (1988).