FILE *freopen(const char *filename
const char *mode
, FILE *stream
Associates a new filename with the given open stream. The old
file in stream is closed. If an error occurs while closing the
file, the error is ignored. The mode argument is the same as
described in the fopen command. Normally used for reassociating
stdin, stdout, or stderr.
On success the pointer to the stream is returned. On error a
null pointer is returned.