fileno(), and many other stdio functions, may be macros
(at least on *BSD).

Don't explicitly qualify it with global scope (::fileno()),
because it causes syntax errors.

<cstdio> doesn't define *most* of these macros.

It still has a macro for fileno(), however, on FreeBSD 6.1,
so even using <cstdio> isn't a fix for this.  Better to
just avoid ::standard_library_function() in general, in
order to be portable.