4.15 fileno—return file descriptor associated with stream

Synopsis

     #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.