fileno(3S) fileno(3S) NAME fileno(), fileno_unlocked() - map stream pointer to file descriptor SYNOPSIS #include <stdio.h> int fileno(FILE *stream); int fileno_unlocked(FILE *stream); DESCRIPTION fileno() returns the integer file descriptor associated with the named stream; see open(2). The following symbolic values in <unistd.h> define the file descriptors associated with stdin, stdout, and stderr when a program is started : STDIN_FILENO Value of zero for standard input, stdin. STDOUT_FILENO Value of 1 for standard output, stdout. STDERR_FILENO Value of 2 for standard error, stderr. fileno_unlocked is identical to fileno except it does not perform any internal locking of the stream for multi-thread applications. fileno_unlocked can be used by multi-thread applications which have already used flockfile() to acquire a mutual exclusion lock for the stream (see flockfile(3S)). RETURN VALUE Upon error, fileno() and fileno_unlocked() return -1. SEE ALSO open(2), flockfile(3S), fopen(3S). STANDARDS CONFORMANCE fileno(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1 Hewlett-Packard Company - 1 - HP-UX Release 10.20: July 1996