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From: ronald@robobar.co.uk (Ronald S H Khoo)
Newsgroups: comp.std.c
Subject: Wanted: struct's address from member's address please.
Message-ID: <1990Nov23.093458.24957@robobar.co.uk>
Date: 23 Nov 90 09:34:58 GMT
Organization: Robobar Ltd., Perivale, Middx., ENGLAND.
Lines: 27

Can someone give me a pointer to relevant bits of the Standard please ?

I'd like to know if

	1) I can have a strictly conforming portable function that returns
	   the address of a structure, given the address of a member of
	   said structure,

	2) Is this function the one I want ? (and is it strictly conforming?)

	#include <stddef.h>

	/* typedefs to define type1 and type2 */

	struct foo {
		type1 first_bit;
		type2 second_bit;
	};

	struct foo *
	func(type2 *arg)
	{
		return  (struct foo *) ((char *)arg -
			offsetof(struct foo, second_bit));
	}
-- 
ronald@robobar.co.uk +44 81 991 1142 (O) +44 71 229 7741 (H)