| FOPEN(3) |
AerieBSD 1.0 Refernce 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 the last character or
as a character between the characters in any of the two-character strings
described above.
This is strictly for compatibility with
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
(
‘a’
or
‘a+’
),
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
repositioning of the stream.
Any created files will have mode
.Pf \\*q Dv 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 descriptor
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 affected 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 original 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
.Pf ( Em 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
The
fdopen();
function conforms to
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);
}
| AerieBSD 1.0 Reference Manual |
May 14 2010 |
FOPEN(3) |