Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: incrementing after a cast
Message-ID: <4674@mimsy.UUCP>
Date: Sat, 6-Dec-86 04:13:52 EST
Article-I.D.: mimsy.4674
Posted: Sat Dec  6 04:13:52 1986
Date-Received: Sun, 7-Dec-86 03:31:44 EST
References: <349@apple.UUCP> <2319@mtgzz.UUCP>
Distribution: net
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 40
Keywords: cast, increment, postincrement

>In article <349@apple.UUCP> kanner@apple.UUCP (Herbert Kanner) writes:
>>		L = *((sometype *) chp)++;
[is illegal---correct]

In article <2319@mtgzz.UUCP> bds@mtgzz.UUCP writes:
>Your confusion comes, I believe, by assuming that precedence and
>grouping rules force one parse to the exclusion of all others

That is a reasonable assumption, for they do.

>By parenthesising the expression:
>
>	L = (*((sometype *) chp))++

This is indeed legal.  It is also not what was written, and not what
was desired.

>Note that this is the parse generated even without the parenthesis.

No: casts and `++' have higher precedence than `*'.  The construct
is semantically illegal, but the compiler will not alter it because
of this.

Incidentally, with a more concrete example:

	int L;
	char *cp;

	L = (*(int *)cp)++;

treats `cp' as though it were a pointer to an integer, obtains the
integer to which that points, copies that value into L, then increments
the integer to which that points.  The code generated is roughly:

	mov	cp,reg
	mov	*reg,L
	add	#1,*reg
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	seismo!mimsy!chris	ARPA/CSNet:	chris@mimsy.umd.edu