From:	"John S. Fine" <johnfine AT erols DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Strange pointer manipulation
Date:	Tue, 26 Jan 1999 10:40:13 -0500
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Message-ID:	<36ADE1DD.13B@erols.com>
References:	<36AD11AA DOT 3876 AT erols DOT com> <wy9r2.317$hd7 DOT 69 AT tundra DOT ops DOT attcanada DOT net>
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DeHackEd wrote:

> There is a built-in C command called offsetof(struct, entry).

Eli Zaretskii <eliz AT is DOT elta DOT co DOT il> wrote:

> No need for any GCC-specific magic: `offsetof' is ANSI C.  It's
> amazing how many people miss that feature.

  Thankyou both.  That is exactly what I needed.  I have been
programming C for many years, frequently wanted that feature
and never knew it was available.

BTW, after I got your messages, it took me a little while to
figure out why it didn't initially work.  Given the name,
I was able to do a search and find it in stddef.h.  (once I
include stddef.h it works).  It turns out it is a macro and
it uses a method similar to the one I tried.  It just does
it in a slightly cleaner way that doesn't confuse the GCC
optimizer, the way mine did.
-- 
http://www.erols.com/johnfine/
http://www.geocities.com/SiliconValley/Peaks/8600/

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