FREOPEN(3C) Standard C Library Functions FREOPEN(3C)
NAME
freopen - open a stream
SYNOPSIS
#include <stdio.h>
FILE *freopen(
const char *filename,
const char *mode,
FILE *stream);
DESCRIPTION
The
freopen() function first attempts to flush the stream and close any
file descriptor associated with
stream. Failure to flush or close the
file successfully is ignored. The error and end-of-file indicators for
the stream are cleared.
The
freopen() function opens the file whose pathname is the string
pointed to by
filename and associates the stream pointed to by
stream with it. The
mode argument is used just as in
fopen(3C).
If
filename is a null pointer and the application conforms to SUSv3 (see
standards(7)), the
freopen() function attempts to change the mode of the
stream to that specified by
mode, as though the name of the file
currently associated with the
stream had been used. This behavior is not
supported by streams that are backed by memory, such as fmemopen
(3C). The following changes of mode are permitted, depending upon the access mode of the file descriptor underlying the stream: o When
+ is specified, the file descriptor mode must be
O_RDWR.
o When
r is specified, the file descriptor mode must be
O_RDONLY or
O_RDWR.
o When
a or
w is specified, the file descriptor mode must be
O_WRONLY or
O_RDWR.
If the filename is a null pointer and the application does not conform to
SUSv3,
freopen() returns a null pointer.
The original stream is closed regardless of whether the subsequent open
succeeds.
After a successful call to the
freopen() function, the orientation of the
stream is cleared, the encoding rule is cleared, and the associated
mbstate_t object is set to describe an initial conversion state.
The largest value that can be represented correctly in an object of type
off_t will be established as the offset maximum in the open file
description.
RETURN VALUES
Upon successful completion,
freopen() returns the value of
stream.
Otherwise, a null pointer is returned and
errno is set to indicate the
error.
ERRORS
The
freopen() function will fail if:
EACCES Search permission is denied on a component of the path
prefix, or the file exists and the permissions specified
by
mode are denied, or the file does not exist and write
permission is denied for the parent directory of the file
to be created.
EBADF The application conforms to SUSv3, the
filename argument
is a null pointer, and either the underlying file
descriptor is not valid or the mode specified when the
underlying file descriptor was opened does not support
the file access modes requested by the
mode argument.
EFAULT The application does not conform to SUSv3 and the
filename argument is a null pointer.
EINTR A signal was caught during
freopen().
EISDIR The named file is a directory and
mode requires write
access.
ELOOP Too many symbolic links were encountered in resolving
path.
EMFILE There are {
OPEN_MAX} file descriptors currently open in
the calling process.
ENAMETOOLONG The length of the
filename exceeds {
PATH_MAX} or a
pathname component is longer than {
NAME_MAX}.
ENFILE The maximum allowable number of files is currently open
in the system.
ENOENT A component of
filename does not name an existing file or
filename is an empty string.
ENOSPC The directory or file system that would contain the new
file cannot be expanded, the file does not exist, and it
was to be created.
ENOTDIR A component of the path prefix is not a directory.
ENXIO The named file is a character special or block special
file, and the device associated with this special file
does not exist.
EOVERFLOW The current value of the file position cannot be
represented correctly in an object of type
off_t.
EROFS The named file resides on a read-only file system and
mode requires write access.
The
freopen() function may fail if:
EINVAL The value of the
mode argument is not valid.
ENAMETOOLONG Pathname resolution of a symbolic link produced an
intermediate result whose length exceeds {
PATH_MAX}.
ENOMEM Insufficient storage space is available.
ENXIO A request was made of a non-existent device, or the
request was outside the capabilities of the device.
ETXTBSY The file is a pure procedure (shared text) file that is
being executed and
mode requires write access.
USAGE
The
freopen() function is typically used to attach the preopened
streams associated with
stdin,
stdout and
stderr to other files. By default
stderr is unbuffered, but the use of
freopen() will cause it to become
buffered or line-buffered.
The
freopen() function has a transitional interface for 64-bit file
offsets. See
lf64(7).
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+
SEE ALSO
fclose(3C),
fdopen(3C),
fopen(3C),
stdio(3C),
attributes(7),
lf64(7),
standards(7) March 25, 2020
FREOPEN(3C)