Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!sun-barr!newstop!sun!amdcad!dvorak.amd.com!proton!tim
From: tim@proton.amd.com (Tim Olson)
Newsgroups: comp.lang.c
Subject: Compound Assignments (was Re: Another <sigh> error!)
Message-ID: <1991Apr6.195901.25255@dvorak.amd.com>
Date: 6 Apr 91 19:59:01 GMT
References: <1991Apr4.205257.15205@mccc.edu>
Sender: usenet@dvorak.amd.com (Usenet News)
Reply-To: tim@amd.com (Tim Olson)
Organization: Advanced Micro Devices, Austin, TX
Lines: 28

In article <1991Apr4.205257.15205@mccc.edu> pjh@mccc.edu (Peter J. Holsberg) writes:
| Where/how does the standard explain that an expression such as
| 
| 	x[i++] *= y;
| 
| has the "x[i++]" part evaluated only once, while an expression such as
| 
| 	x *= y;
| 
| has the "x" part evaluated twice, as in
| 
| 	x = x * y;

In the second example, "x" is not evaluated twice -- it is evaluated
only once, just as in the first example.  The standard says just this
in 3.3.16.2 (Compound assignment):

  Semantics

	A compound assignment of the form E1 op= E2 differs from the
	simple assignment expression E1 = E1 op (E2) only in that the
	lvalue E1 is evaluated only once.


--
	-- Tim Olson
	Advanced Micro Devices
	(tim@amd.com)