freopen - open a stream
FILE *freopen(const char *filename, const char *mode, FILE
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
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).
The original stream is closed regardless of whether the sub-
sequent open succeeds.
After a successful call to the freopen() function, the
orientation of the stream is cleared and the associated
mbstate_t object is set to describe an initial conversion
The largest value that can be represented correctly in an
object of type off_t will be established as the offset max-
imum in the open file description.
Upon successful completion, freopen() returns the value of
stream. Otherwise, a null pointer is returned and errno is
set to indicate the error.
The freopen() function will fail if:
Search permission is denied on a component of the path
prefix, or the file exists and the permissions speci-
fied by mode are denied, or the file does not exist
and write permission is denied for the parent direc-
tory of the file to be created.
EINTR A signal was caught during freopen().
The named file is a directory and mode requires write
ELOOP Too many symbolic links were encountered in resolving
There are OPEN_MAX file descriptors currently open in
the calling process.
The length of the filename exceeds PATH_MAX or a path-
name component is longer than NAME_MAX.
The maximum allowable number of files is currently
open in the system.
A component of filename does not name an existing file
or filename is an empty string.
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.
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.
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:
The value of the mode argument is not valid.
Pathname resolution of a symbolic link produced an
intermediate result whose length exceeds PATH_MAX.
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.
The file is a pure procedure (shared text) file that
is being executed and mode requires write access.
The freopen() function is typically used to attach the preo-
pened 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(5).
When a UFS file system is mounted with logging enabled, file
system transactions that free blocks from files might not
actually add those freed blocks to the file system's free
list until some unspecified time in the future. This
behavior improves file system performance but does not con-
form to the POSIX, Single UNIX Specification, SPARC Confor-
mance Definition, System V Application Binary Interface,
System V Interface Definition, and X/Open Portability Guide
Standards, which require that freed space be available
immediately. To enable standards conformance regarding file
deletions or to address the problem of not being able to
grow files on a relatively full UFS file system even after
files have been deleted, disable UFS logging (see
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | MT-Safe |
mount_ufs(1M), fclose(3C), fdopen(3C), fopen(3C), stdio(3C),
Man(1) output converted with