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From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.lang.c
Subject: Re: Standard Clarification
Message-ID: <1424@crdos1.crd.ge.COM>
Date: 24 Oct 89 17:35:17 GMT
References: <20974@gryphon.COM> <1150@crdos1.crd.ge.COM> <23218@cup.portal.com> <1989Oct21.233915.23217@utzoo.uucp>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Organization: GE Corp R&D Center
Lines: 42

In article <1989Oct21.233915.23217@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes:

|  Section 3.8.3 (Oct 1988 draft, roughly current except for wording changes):
|  
|  "If a # preprocessing token, followed by an identifier, occurs lexically
|  at the point at which a preprocessing directive could begin, the identifier
|  is not subject to macro replacement."
|  
|  In other words, ANSI C specifically says that it *doesn't* work.

Another thing doesn't work, although it would be useful. If you have
macros of the form:

	#define FOO		123
	#define BAR		FOO
	#define DEMO(c) 	printf("Demo:"#c"\n")
then:
	DEMO(BAR);
does not do a substitution of FOO for BAR, nor 123 for FOO. To make this
work the value of the argument must be forced to be evaluated first.
	#define XDEMO(c)	DEMO(c)
and:
	XDEMO(BAR);
now substitutes 123. This is how I would expect it to work, from the
section you quote. Both gcc and a beta of MSC work just that way.

Test prog for the terminally curious:

#define FOO		123
#define BAR		FOO
#define X(c)		printf("X:"#c"\n")
#define TMP(c)		X(c)

X(FOO);
X(BAR);
TMP(BAR);

-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
"The world is filled with fools. They blindly follow their so-called
'reason' in the face of the church and common sense. Any fool can see
that the world is flat!" - anon