The functionality described on this reference page is aligned with
the ISO C standard. Any conflict between the
requirements described here and the ISO C standard is unintentional.
This volume of IEEE Std 1003.1-2001 defers to
the ISO C standard.
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 subsequent
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 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. <img
src="../images/opt-end.gif" alt="[Option End]" border="0">
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. <img
src="../images/opt-end.gif" alt="[Option End]" border="0">
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.
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 ALSO
fclose() , 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 .
