Path: utzoo!utgpu!utcsri!flaps
From: flaps@utcsri.UUCP (Alan J Rosenthal)
Newsgroups: comp.lang.c
Subject: Re: == vs =
Message-ID: <5981@utcsri.UUCP>
Date: 11 Apr 88 05:41:09 GMT
Article-I.D.: utcsri.5981
Posted: Mon Apr 11 01:41:09 1988
References: <11216@brl-adm.ARPA> <2111@chinet.UUCP> <4403@garfield.UUCP> <226@hotlr.ATT> <130@obie.UUCP>
Reply-To: flaps@dgp.toronto.edu (Alan J Rosenthal)
Organization: University of Toronto
Lines: 26
Summary: 


In article <130@obie.UUCP> wes@obie.UUCP (Barnacle Wes) writes:
>The one thing that everyone seems to have forgotten in this discussion
>is that `=' is NOT always invalid in an if clause:
>
>    if (status = *statreg) {
 [ where what is intended is assignment followed by testing of the result ]

I think this is better written as "if ((status = *statreg))"; some
people even recommend "if ((status = *statreg), status)".%

If you write the if as "if (a = b)", many readers of your code
(possibly including yourself) will first think "aha, this is a typo".
Many other readers will read it as "if (a == b)".  It is therefore a
good idea to use a visually distinct form.  The two forms I list above
both result from the idea that `=' should not be the top level operator
in a conditional expression.

ajr

%  The semantics of this second version differs from the original if
   `status' is volatile.  If you use volatile in a way that could come
   up here, you might not want to adopt this second syntax.

--
"An aardvark in the nose is worth two in the phototypesetter."