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From: hahn@fred (Jonathan Hahn)
Newsgroups: comp.lang.c
Subject: Re: structure element offsets
Message-ID: <768@nike.UUCP>
Date: Tue, 25-Nov-86 20:32:30 EST
Article-I.D.: nike.768
Posted: Tue Nov 25 20:32:30 1986
Date-Received: Tue, 25-Nov-86 22:40:53 EST
References: <1096@spice.cs.cmu.edu>
Sender: usenet@nike.UUCP
Reply-To: hahn@ames-nas.arpa (Jonathan Hahn)
Organization: NASA Ames, Mountain View, CA
Lines: 13
Keywords: structure, offset

In article <1096@spice.cs.cmu.edu> bader@spice.cs.cmu.edu (Miles Bader) writes:
>Is there any way of finding the offset of a structure element from
>the beginning of a structure in a portable AND efficient way?

Try:

#define OFFSET(elem, type)	(&(((type *)0)->elem))

This utilizes a pointer of address 0, for which the address of the
element reference yeilds the offset of the element.

-jonathan hahn
hahn@ames-nas.arpa