Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!munnari.oz.au!goanna!ok
From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: Re: Need macro to get offset within a structure
Message-ID: <4809@goanna.cs.rmit.oz.au>
Date: 21 Feb 91 05:48:44 GMT
References: <1991Feb16.232713.6001@runx.oz.au> <ENAG.91Feb19131201@holmenkollen.ifi.uio.no>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 11

In article <ENAG.91Feb19131201@holmenkollen.ifi.uio.no>, enag@ifi.uio.no (Erik Naggum) writes:
> I snatched this from /local/lib/gcc-include/stddef.h.
> #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
> This works like a charm on a vast number of compilers I've used.

offsetof() being a required part of ANSI C (if you use the right header),
it's clearly the right interface.  You'll want an #if __STDC__ so that you
get the "official" version when it's there, as the cast of zero is not
portable.
-- 
Professional programming is paranoid programming