Path: utzoo!mnetor!uunet!husc6!necntc!ima!haddock!karl
From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: macros with parameters in MSC 5.0
Message-ID: <2645@haddock.ISC.COM>
Date: 19 Feb 88 18:01:49 GMT
References: <11879@brl-adm.ARPA> <7277@brl-smoke.ARPA>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 23

In article <7277@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes:
>In article <11879@brl-adm.ARPA> jbaker@ee.UCLA.EDU (Joe Baker) writes:
>>#define ctl(c) ('c'&037)
>
>Yes, whoever did this was deliberately violating the K&R rules

I looked it up when I first saw this hack, and I concluded that K&R didn't
establish an unambiguous rule.  The book says that macros are not expanded
inside strings, but I don't think it specifies whether macro *arguments* are
expanded inside strings within the macro.

>With ANSI C, or any C preprocessor that includes the stringizing
>feature, you can make the original usage work by
>	#define ctl(c) (#c[0]&037)
>which would cause
>	case ctl(G):
>to expand to
>	case ("G"[0]&037):

Umm, I believe that according to the C rules, that's a non-constant expression
(and hence illegal as a case label).

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint