FOPEN(3) | Library Functions Manual | FOPEN(3) |
fopen
, fdopen
,
freopen
—
#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);
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, which may be followed by additional modifiers as indicated below:
a
”a+
”r
”r+
”w
”w+
”After one of those, the mode string can also include one or more of the following modifier letters:
O_CLOEXEC
) flag of the file descriptor, which
means that it will not be available after an
exec(3) system call. This is a
non ANSI X3.159-1989
(“ANSI C89”) extension.fopen
() to regular files; if the file opened is
not a regular file, fopen
() will close it, and
fail. This is a non ANSI X3.159-1989
(“ANSI C89”) extension.O_NOFOLLOW
) flag of the
file descriptor, which means that if the last path component is a symbolic
link, it will not be followed. This is a non ANSI
X3.159-1989 (“ANSI C89”) extension.O_EXCL
) which means that the file will
not be created if it already exists. In that case
fopen
() will fail.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(2) value.
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 repositioning 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 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.
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).
Input and output against the opened stream will be fully buffered, unless it refers to an interactive terminal device, or a different kind of buffering is specified in the environment. See setvbuf(3) for additional details.
fopen
(),
fdopen
() and freopen
() return
a FILE pointer. Otherwise, NULL
is returned and the
global variable errno is set to indicate the error.
EFTYPE
]EINVAL
]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).
fopen
() and freopen
()
functions conform to ANSI X3.159-1989
(“ANSI C89”). All three functions are specified in
IEEE Std 1003.1-2008 (“POSIX.1”).
fopen
() function appeared in
Version 1 AT&T UNIX.
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); }
September 2, 2019 | NetBSD 9.2 |