fileno(3) -- Linux man page
NAMEclearerr, feof, ferror, fileno - check and reset stream status
DESCRIPTIONThe function clearerr clears the end-of-file and error indicators for the stream pointed to by stream.
The function feof tests the end-of-file indicator for the stream pointed to by stream, returning non-zero if it is set. The end-of-file indicator can only be cleared by the function clearerr.
The function ferror tests the error indicator for the stream pointed to by stream, returning non-zero if it is set. The error indicator can only be reset by the clearerr function.
The function fileno examines the argument stream and returns its integer descriptor.
For non-locking counterparts, see unlocked_stdio(3).
ERRORSThese functions should not fail and do not set the external variable errno. (However, in case fileno detects that its argument is not a valid stream, it must return -1 and set errno to EBADF.)
CONFORMING TOThe functions clearerr, feof, and ferror conform to X3.159-1989 (``ANSI C'').
SEE ALSOopen(2), unlocked_stdio(3), stdio(3)