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From: 6sigma2@polari.UUCP (Brian Matthews)
Newsgroups: comp.lang.c
Subject: Re: Array bounds checking: what is legal
Message-ID: <2461@polari.UUCP>
Date: 3 Sep 90 23:16:49 GMT
References: <26196@mimsy.umd.edu> <29051@nigel.ee.udel.edu> <26327@mimsy.umd.edu>
Organization: Seattle Online Public Unix (206) 328-4944
Lines: 21

In article <26327@mimsy.umd.edu> chris@mimsy.umd.edu (Chris Torek) writes:
|Correct.  Given `int a[4];', the following holds:
|	int *p = a;			/* legal */
|	a[0], a[1], a[2], a[3];		/* all legal */
|	p[0], p[1], p[2], p[3];		/* all legal */
|	p = &a[4];			/* legal */
|	*p;				/* illegal (a[4] does not exist) */
|	p--;				/* legal */
|	p = a;				/* legal */
|	p--;				/* illegal */
|	p = &a[4];			/* legal */
|	p[-4], p[-3], p[-2], p[-1];	/* all legal */

A minor clarification - where Chris says "illegal", read "undefined".
Admittedly a minor point, but "illegal" might lead one to believe the
compiler won't accept the code in question.  "Undefined" means the
compiler may or may not accept the code, and if accepted, the resulting
machine code may or may not do something "useful", which is actually
the case.
-- 
Brian L. Matthews	blm@6sceng.UUCP