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Path: utzoo!watmath!clyde!ima!haddock!karl
From: karl@haddock.UUCP
Newsgroups: comp.lang.c
Subject: Re: RMS comments to X3J11
Message-ID: <303@haddock.UUCP>
Date: Thu, 15-Jan-87 18:20:24 EST
Article-I.D.: haddock.303
Posted: Thu Jan 15 18:20:24 1987
Date-Received: Fri, 16-Jan-87 06:53:26 EST
References: <2144@brl-adm.ARPA> <5497@brl-smoke.ARPA> <1258@ho95e.UUCP>
Reply-To: karl@haddock.ISC.COM.UUCP (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 26

In article <1258@ho95e.UUCP> wcs@ho95e.UUCP (Bill Stewart) writes:
>Doug's suggestion was to have such constants start with _sys_ and _mach_,
>e.g. _sys_43bsd or _mach_vax.  As an alternative, why not let
>_sys_ and _machine_ be preprocessor variables, leading to
>	#define	_sys_	SysVR2
>	#define	_machine_	u3b2
>and
>	#if _machine_ = vax
[I presume that was a typo for "==".  --kwzh]

Your suggestion is incomplete.  In cpp as currently implemented, your "#if"
would expand into "#if u3b2 == vax" which would be true (!) since tokens with
no definitions are evaluated as zero.

Perhaps you're assuming a hook in cpp to recognize such a comparison and use
the token names instead of their values.  (Perhaps you even intended "=", as
opposed to "==", to distinguish this operation?  I hope not.)  I think such a
rule is too confusing.

Someone else already suggested a variant that I think is more viable:
	#define	_machine_	"u3b2"
could be tested by some comparison operator.  Either "==" or "strcmp(,)==0"
could be used, but since the interpretation is not identical to that of C, I
will suggest a new preprocessor operator "#==".

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