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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: finding offset of a member in C structures
Message-ID: <16194@smoke.brl.mil>
Date: 20 May 91 04:09:18 GMT
References: <1276@unisql.UUCP>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 19

In article <1276@unisql.UUCP> pckim@unisql.UUCP (Pyung-Chul Kim) writes:
-	struct a_struct {
-		short	member1;
-		char	member2;
-		int	memner3;
-	};
-can I get the offset of member2 at *compiling time* and *portably* ?

Yes, but you shouldn't very often need to do so.

-It is possible to provide a compiler operator:
-	offsetof(member_name,structure_type_name)
-as it provides 'sizeof' operator.
-Do you know if there is a compiler operator like above, or is there any
-alternative solution.

Standard C provides an offsetof() macro, but you don't really need one.
	struct a_struct foo;
	int offset2 = (char *)&foo.member2 - (char *)&foo; /* for example */