Tribblix: manual page: freopen.3c

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