Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

boost/pending/cstddef.hpp

// -*- C++ -*- forwarding header.

#ifndef BOOST_CSTDDEF_HPP
#define BOOST_CSTDDEF_HPP

#if defined(__sgi) && !defined(__GNUC__)
# include <stddef.h>
#else
# include <cstddef>
#endif

#endif