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From: cobb@utcsstat.UUCP ()
Newsgroups: net.lang.c
Subject: Re: pointer question
Message-ID: <1836@utcsstat.UUCP>
Date: Mon, 9-Apr-84 00:50:41 EST
Article-I.D.: utcsstat.1836
Posted: Mon Apr  9 00:50:41 1984
Date-Received: Mon, 9-Apr-84 01:40:49 EST
References: <7624@mgweed.UUCP> <937@inuxc.UUCP>, <155@hercules.UUCP>
Organization: U. of Toronto, Canada
Lines: 35

If anyone out there is still not convinced about "p = p + 4" portability,
after reading Archie's explanation (Archie Lachner), I submit the
following:
	given a structure struct X {
					int a;
					int b;
					int c;
				}
	with a register pointer p of type X;

	p = p + 4 	generates

	addl	$48,reg_n,reg_n		; add decimal 48 to register
					; VAX - berkeley C compiler

and
	add	$30,reg_n		; add octal 30 (24) to register
					; 11/70 - Bell C Compiler

	As you might've guessed, reg_n is p.
	In each case, the actual value added is <size of struct> * 4.

	Thus, any fears about "p = p + n" is quite unfounded.
	In fact, K&R states that a construct p[i] is actually
	treated as p + i.

If this is still not convincing enough, c'est la vie !!

	OZ

				Ozan S. Yigit (utzoo!utcsstat!cobb)
				(utzoo!yetti!ozan)
				Dept. of Computer Science
				York University