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Path: utzoo!mnetor!seismo!husc6!necntc!ima!haddock!karl
From: karl@haddock.UUCP (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Style question re common C expression.
Message-ID: <608@haddock.UUCP>
Date: Mon, 22-Jun-87 20:54:14 EDT
Article-I.D.: haddock.608
Posted: Mon Jun 22 20:54:14 1987
Date-Received: Wed, 24-Jun-87 03:58:45 EDT
References: <4934@utcsri.UUCP> <8164@utzoo.UUCP>
Reply-To: karl@haddock.ISC.COM.UUCP (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 28
Keywords: STREQ

In article <8164@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>> ... like the standard "#define STREQ(s,t)(strcmp(s,t) == 0)"?
>
>This is slightly off the topic, but note two things:
>
>First, that should be "(strcmp((s),(t)) == 0)" for safety's sake, although
>in this case trouble is unlikely.

Unlikely?  I think in this case it's impossible.  But you're right in that
it's a good habit to get into, and it certainly doesn't hurt.

>Second, if you don't indulge in the perversion of routinely using side
>effects within expressions, then a still better form is:
>
>#define	STREQ(a, b)	(*(a) == *(b) && strcmp((a), (b)) == 0)

Some people would phrase that the other way around: "If you don't indulge in
the perversion of writing macros that evaluate their arguments more than once,
then you can write f(p++), using them just like functions."

>This makes a considerable speed difference in programs that use strings
>a lot, since string comparisons usually fail on the very first character.

Of course, a really good compiler will make "strcmp" a builtin, giving you the
same speed improvement without sacrificing any of the calling contexts.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint
(Btw, the name "STREQ" isn't all that standard.  I spell it "streq", myself.)