Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ulysses.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!jss
From: jss@ulysses.UUCP (Jerry Schwarz)
Newsgroups: net.lang.c
Subject: Re: Casting a postdecrement operand
Message-ID: <1295@ulysses.UUCP>
Date: Sun, 15-Jun-86 15:10:53 EDT
Article-I.D.: ulysses.1295
Posted: Sun Jun 15 15:10:53 1986
Date-Received: Tue, 17-Jun-86 10:49:35 EDT
References: <114@romp.UUCP> <2842@utcsri.UUCP> <1273@ulysses.UUCP> <786@steinmetz.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 19

> 
> The variable 'cbap' is a pointer. The cast '(struct abc *)' is a
> pointer cast. I can use '((struct abc *)cbap)' with indirects and
> subscripts and anywhere that I can use an Lvalue, so I really believe
> that the expression is legal.
> 	-bill davidsen

Being a pointer value is not the same as being an lvalue. The places
that require lvalues are left hand side of assignments, and operands
of the increment and decrement operations. In none of these locations
is '((struct abc*)cbap)' legal.

If p is an expression with a (data) pointer type then *p will
be an lvalue, so 
	++ *((struct abc**)&cbab) 
will modify cbab.

Jerry Schwarz
Bell Labs, MH