Path: utzoo!utgpu!water!watmath!clyde!att!att-ih!pacbell!ames!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: Is &a[NTHINGS] legal
Message-ID: <11305@mimsy.UUCP>
Date: 2 May 88 04:09:07 GMT
References: <12074@tut.cis.ohio-state.edu> <11289@mimsy.UUCP> <5997@utcsri.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 31

>>In article <12074@tut.cis.ohio-state.edu> lvc@tut.cis.ohio-state.edu
>>(Lawrence V. Cipriani) writes:
>>>	for (p = a; p < &a[NTHINGS]; p++)	/* legal? */

>In article <11289@mimsy.UUCP> I answered:
>>Yes.

In article <5997@utcsri.UUCP> norvell@utcsri.UUCP (Theodore Stevens Norvell)
writes:
>But, doesn't the draft ... also say that p+i (where p is a pointer)
>can only be dereferenced if it points to the same array as does p?

Yes.

>Since &a[NTHINGS] translates to &(*(a+NTHINGS))

No, not the way you mean this.  `Is equivalent to', not `evaluates as':
the indirection does not occur.  Only the address computation occurs;
the value at a+NTHINGS is not examined.

>... the dereference is undefined.

True.  It also does not occur.

>This allows array bounds checking in ANSI C.

Bounds checking is still possible, but &a[NTHINGS] must be allowed,
while both a[NTHINGS] and &a[NTHINGS+1] should be rejected.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris