FREOPEN(P) POSIX Programmer's Manual FREOPEN(P)NAMEfreopen - open a stream
SYNOPSIS
#include <stdio.h>
FILE *freopen(const char *restrict filename, const char *restrict mode,
FILE *restrict stream);
DESCRIPTION
The freopen() function shall first attempt to flush the stream and
close any file descriptor associated with stream. Failure to flush or
close the file descriptor successfully shall be ignored. The error and
end-of-file indicators for the stream shall be cleared.
The freopen() function shall open the file whose pathname is the string
pointed to by filename and associate the stream pointed to by stream
with it. The mode argument shall be used just as in fopen().
The original stream shall be closed regardless of whether the subse‐
quent open succeeds.
If filename is a null pointer, the freopen() function shall attempt to
change the mode of the stream to that specified by mode, as if the name
of the file currently associated with the stream had been used. It is
implementation-defined which changes of mode are permitted (if any),
and under what circumstances.
After a successful call to the freopen() function, the orientation of
the stream shall be cleared, the encoding rule shall be cleared,
and the associated mbstate_t object shall be set to describe an initial
conversion state.
The largest value that can be represented correctly in an object of
type off_t shall be established as the offset maximum in the open file
description.
RETURN VALUE
Upon successful completion, freopen() shall return the value of stream.
Otherwise, a null pointer shall be returned, and errno shall be set
to indicate the error.
ERRORS
The freopen() function shall 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.
EINTR A signal was caught during freopen().
EISDIR The named file is a directory and mode requires write access.
ELOOP A loop exists in symbolic links encountered during resolution of
the path argument.
EMFILE {OPEN_MAX} file descriptors are currently open in the calling
process.
ENAMETOOLONG
The length of the filename argument 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 file‐
name 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 named file is a regular file and the size of the file 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.
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the path argument.
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 nonexistent 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.
The following sections are informative.
EXAMPLES
Directing Standard Output to a File
The following example logs all standard output to the /tmp/logfile
file.
#include <stdio.h>
...
FILE *fp;
...
fp = freopen ("/tmp/logfile", "a+", stdout);
...
APPLICATION USAGE
The freopen() function is typically used to attach the preopened
streams associated with stdin, stdout, and stderr to other files.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOfclose() , fopen() , fdopen() , mbsinit() , the Base Definitions volume
of IEEE Std 1003.1-2001, <stdio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 FREOPEN(P)
