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From: ts@cup.portal.com (Tim W Smith)
Newsgroups: comp.lang.c
Subject: Re: offsetof() operator.  A tricky question.
Message-ID: <28008@cup.portal.com>
Date: 18 Mar 90 11:44:01 GMT
References: <8ega02MX90Tk01@amdahl.uts.amdahl.com> <695@shuldig.Huji.Ac.IL>
Organization: The Portal System (TM)
Lines: 20

< The answer could be simple and I used several times, do this:
< 
< struct astruct *ap;
< 
< ap = NULL;
< 
< offsetof_member0 = &ap->member0; /* zero offset */
< offsetof_member1 = &ap->member1; /* sizeof(member0) */
< 
< An offsetof() operator would be quite handy here. But until then you can
< use this with a good portability of your programs.

It IS simple.  It is also wrong.

If you want to have at least a small chance of working across different
machines, try this:

	offsetof_member0 = (ulong)&ap->member0 - (ulong)ap;
	...
						Tim Smith