Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!brl-smoke!gwyn
From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: Is &a[NTHINGS] legal
Message-ID: <7806@brl-smoke.ARPA>
Date: 30 Apr 88 16:06:59 GMT
References: <12074@tut.cis.ohio-state.edu>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 20

In article <12074@tut.cis.ohio-state.edu> lvc@tut.cis.ohio-state.edu (Lawrence V. Cipriani) writes:
>Is it legal to apply the & (address of) operator to an array
>element that is non-existent?  Given:
>	sometype a[NTHINGS], *p;
>Should:
>	for (p = a; p < &a[NTHINGS]; p++)	/* 1 */
>be written as:
>	for (p = a; p <= &a[NTHINGS-1]; p++)	/* 2 */
>		...
>Will 1 be guaranteed to work in ANSI-C?

Yes, it is.  This kind of code is quite pervasive, and if you
consider that NTHINGS might have been defined as 0 it is impossible
to avoid (in fact in that situation your case 2 is invalid).

Every object must have at least one addressable cell beyond it,
but not necessarily in front of it.  The reason the latter is not
required is that &a[-1] may be MANY bytes in front of allocated
storage if the array element is large, but &a[NTHINGS] will be
just one byte past the valid array locations.