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From: pckim@unisql.UUCP (Pyung-Chul Kim)
Newsgroups: comp.lang.c
Subject: finding offset of a member in C structures
Message-ID: <1276@unisql.UUCP>
Date: 17 May 91 20:13:38 GMT
Reply-To: pckim@unisql.UUCP (Pyung-Chul Kim)
Organization: UniSQL, Inc., Austin, Texas
Lines: 36


I have a question about finding offset of a member in a structure of C.
For example, in the following structure, `a_struct',

	struct a_struct {
		short	member1;
		char	member2;
		int	memner3;
	};

can I get the offset of member2 at *compiling time* and *portably* ?
The offset may be different for machines and compilers because
they employ different member alignment schemes.
I think there is no reason for C compiler not to provide such facility.
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.

Thanks in advance.

P.S.
we can get the offset at run_time like following:
#define offsetof(a,b)	((int)&((b *)0->a))
But, what I mean is *at compile time*.

-- 
Pyung-Chul Kim

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