Path: utzoo!utgpu!utcsri!norvell
From: norvell@utcsri.UUCP (Theodore Stevens Norvell)
Newsgroups: comp.lang.c
Subject: Re: Is &a[NTHINGS] legal
Message-ID: <5997@utcsri.UUCP>
Date: 1 May 88 21:37:19 GMT
Article-I.D.: utcsri.5997
Posted: Sun May  1 17:37:19 1988
References: <12074@tut.cis.ohio-state.edu> <11289@mimsy.UUCP>
Reply-To: norvell@utcsri.UUCP (Theodore Stevens Norvell)
Organization: CSRI, University of Toronto
Lines: 18
Summary: 

In article <11289@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
>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?
>>	for (p = a; p < &a[NTHINGS]; p++)	/* 1 */
>>Will 1 be guaranteed to work in ANSI-C?
>
>Yes.  If necessary, the compiler will put a one-byte (or word or
>whatever) shim after the array in that array's address space, so
>that &a[NTHINGS] will be meaningful.

But, doesn't the draft (my copy is from November) also say that p+i
(where p is a pointer) can only be dereferenced if it points to the
same array as does p? Since &a[NTHINGS] translates to &(*(a+NTHINGS))
and a+NTHINGS does not point to the same array as does a, the dereference
is undefined.  This allows array bounds checking in ANSI C.
Try     for(p = a; p < a+NTHINGS; p++)  /* 3 */