fileno—return file descriptor associated with stream #include <stdio.h>
int fileno(FILE *fp);
Description
You can use fileno to return the file descriptor identified by fp.
Returns
fileno returns a non-negative integer when successful.
If fp is not an open stream, fileno returns -1.
Portability
fileno is not part of ANSI C.
POSIX requires fileno.
Supporting OS subroutines required: none.