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
Thefopen()
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. It
“
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. This is strictly for compatibility with ANSI X3.159-1989 (“ANSI C89”) 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 descriptor,
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(), orfreopen() 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
STANDARDS
The fopen() and
freopen() functions conform to ANSI
X3.159-1989 (“ANSI C89”). The
fdopen() function conforms to IEEE
Std 1003.1-1988 (“POSIX.1”).