Synopsis

#include <stdio.h>

FILE *freopen(const char *filename, const char *mode, FILE *stream);

Description

The freopen() function associates a new filename with the given open stream and at the same time closes the old file in stream.

Arguments:

filename - a pathname to the file to be opened,
mode - the required mode of the file,
stream - the pointer to a FILE object that identifies the stream to be reopened

The freopen() function first attempts to flush the stream associated with stream as if by a call to fflush(stream). Failure to flush the stream successfully is ignored. If filename is not a null pointer, freopen() closes any file descriptor associated with stream. Failure to close the file descriptor successfully is ignored. The error and end-of-file indicators for the stream are cleared.

The freopen() function opens the file whose filename 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().

The original stream is closed regardless of whether the subsequent open succeeds.

If filename is a null pointer, the freopen() function attempts 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. In this case, the file descriptor associated with the stream need not be closed if the call to freopen() 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.

If filename is not a null pointer, or if filename is a null pointer and the specified mode change necessitates the file descriptor associated with the stream to be closed and reopened, the file descriptor associated with the reopened stream is allocated and opened as if by a call to open() with the following flags:






























freopen() Mode open() Flags
r or rb O_RDONLY
w or wb O_WRONLY|O_CREAT|O_TRUNC
a or ab O_WRONLY|O_CREAT|O_APPEND
r+ or rb+ or r+b O_RDWR
w+ or wb+ or w+b O_RDWR|O_CREAT|O_TRUNC
a+ or ab+ or a+b O_RDWR|O_CREAT|O_APPEND

Return value

The value of stream on success. Otherwise, a null pointer is returned, and errno is set to indicate the error.

Errors

[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 file descriptor underlying the stream is not a valid file descriptor when pathname is a null pointer.
[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 filename argument.
[EMFILE] All file descriptors available to the process are currently open.
[ENAMETOOLONG] The length of a component of a filename is longer than {NAME_MAX}.
[ENFILE] The maximum allowable number of files is currently open in the system.
[ENOENT] The mode string begins with 'r' and a component of filename does not name an existing file, or mode begins with 'w' or 'a' and a component of the path prefix of pathname does not name an existing file, or pathname is an empty string.
[ENOENT] or [ENOTDIR] The filename argument contains at least one non- character and ends with one or more trailing characters. If filename without the trailing characters would name an existing file, an [ENOENT] error does not occur.
[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 names an existing file that is neither a directory nor a symbolic link to a directory, or the filename argument contains at least one non- character and ends with one or more trailing characters and the last filename component names an existing file that is neither a directory nor a symbolic link to 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.
[EBADF] The mode with which the file descriptor underlying the stream was opened does not support the requested mode when filename is a null pointer.
[EINVAL] The value of the mode argument is not valid.
[ELOOP] More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the file argument.
[ENAMETOOLONG] The length of a filename exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that 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.

Implementation tasks

  • Implement error handling for the function.