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From: kanner@apple.UUCP (Herbert Kanner)
Newsgroups: comp.lang.c
Subject: incrementing after a cast
Message-ID: <349@apple.UUCP>
Date: Wed, 3-Dec-86 14:37:17 EST
Article-I.D.: apple.349
Posted: Wed Dec  3 14:37:17 1986
Date-Received: Thu, 4-Dec-86 00:16:40 EST
Distribution: net
Organization: Apple Computer, Inc., Cupertino, USA
Lines: 24
Keywords: cast, increment, postincrement


We would like to solicit some opinions on the legality of the
following, which is one way of implementing varargs for, e.g., printf:

	foo()
	{
		sometype L;
		char *chp;

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

Both the portable C compiler and lint happily accept this construct.
The idea of the cast is to force chp to be incremented by the size of
sometype.

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.
-- 
Herb Kanner
Apple Computer, Inc.
{idi, ios, nsc}!apple!kanner