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Path: utzoo!mnetor!seismo!rutgers!clyde!cbatt!ihnp4!drutx!mtuxo!mtgzz!bds
From: bds@mtgzz.UUCP
Newsgroups: comp.lang.c
Subject: Re: incrementing after a cast
Message-ID: <2319@mtgzz.UUCP>
Date: Fri, 5-Dec-86 10:12:23 EST
Article-I.D.: mtgzz.2319
Posted: Fri Dec  5 10:12:23 1986
Date-Received: Sat, 6-Dec-86 03:21:49 EST
References: <349@apple.UUCP>
Distribution: net
Organization: AT&T, Middletown NJ
Lines: 29
Keywords: cast, increment, postincrement
Summary: *(type)var is an lvalue

In article <349@apple.UUCP>, kanner@apple.UUCP (Herbert Kanner) writes:
> 	foo()
> 	{
> 		sometype L;
> 		char *chp;
> 
> 		L = *((sometype *) chp)++;
> 	}
> ...
> Our problem arises with the allegation that K&R makes this construct
> illegal.  On page 214 (syntax summary), the only legal context for ++
> is given to be lvalue++, and (type-name) expression is a case of
> expression which, according to that syntax, cannot be an lvalue.

Your confusion comes, I believe, by assuming that precedence and
grouping rules force one parse to the exclusion of all others
(i.e. that the expression is parsed as *(((sometype *) chp)++) which
is illegal). By parenthesising the expression:

	L = (*((sometype *) chp))++

Then using the rules on page 214 the parse is:

	expression : (type-name) expression
	lvalue : * expression
	expression : lvalue++

Note that this is the parse generated even without the parenthesis.
Happily, it is the one you want.