Xref: utzoo comp.lang.c:8392 comp.unix.questions:6160
Path: utzoo!mnetor!uunet!husc6!purdue!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c,comp.unix.questions
Subject: Re: BSD C compiler bug
Message-ID: <10754@mimsy.UUCP>
Date: 21 Mar 88 18:22:17 GMT
References: <570@mtxinu.UUCP> <10747@mimsy.UUCP> <7507@brl-smoke.ARPA>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 34

>In article <10747@mimsy.UUCP> I said
[	char *p; p = (0, 0); ]
>>The 11 Jan 1988 draft of the dpANS [disallows `,' in] constant
>>expressions (p. 56):

In article <7507@brl-smoke.ARPA> gwyn@brl-smoke.ARPA (Doug Gwyn) writes:
>What do constant expressions have to do with it?

Constant expressions have *everything* to do with it!

How do you create a nil pointer of type T in C?  Answer: put the
integer constant `0' in a pointer context (assignment or comparison, or
[dpANS] argument to a function that has a prototype in scope).  What is
`the integer constant 0'?  Clearly this is any constant expression
whose value is zero and whose type is one of the integral types {char,
short, int, long} or their signed or unsigned variants.  The
expression

	(0, 0)

certainly has the value zero and an integral type, but according to
the dpANS, it is not a constant expression.  Hence it cannot be `the
integer constant zero'; it is merely an integer expression whose value
is zero.  The situation is thus the same as if one were to write

	char *p;
	int zero = 0;
	p = zero;

I have not found anything in the draft standard to contradict
this reasoning.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris