Path: utzoo!attcan!uunet!lll-winken!ames!pasteur!ucbvax!ulysses!gsf
From: gsf@ulysses.homer.nj.att.com (Glenn Fowler[eww])
Newsgroups: comp.lang.c
Subject: Re: Preprocessor question
Summary: unless subject to # or ##
Message-ID: <11125@ulysses.homer.nj.att.com>
Date: 20 Jan 89 02:55:05 GMT
References: <531@ole.UUCP> <9433@smoke.BRL.MIL>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 33

In article <9433@smoke.BRL.MIL>, gwyn@smoke.BRL.MIL (Doug Gwyn ) writes:
> In article <531@ole.UUCP> ray@ole.UUCP (Ray Berry) writes:
> >#define VAL 3
> >#define STR(x) #x
> >  puts("val is " STR(VAL));
> >   Turbo C produces "3" for STR(VAL); Microsoft produces "VAL" and 
> >leaves it at that.  
> >   Which behavior is correct?
> 
> "Before being substituted, each argument's preprocessing tokens are
> completely macro replaced as if they formed the rest of the
> translation unit; no other preprocessing tokens are available."
> 
> So VAL is first expanded to 3 then the #3 is performed to produce
> "3".
unless things changed from the 86 draft, macro arguments subject to the
# and ## operators are not expanded before the # and ## operations, so
the above eventually produces:

	puts ( "val is VAL" ) ;

to get VAL expanded add one more macro level:

	#define STR(x)	#x
	#define XSTR(x)	STR(x)
	puts(STR(VAL) " is " XSTR(VAL));

to eventually get:

	puts ( "VAL is 3" ) ;
-- 
Glenn Fowler    (201)-582-2195    AT&T Bell Laboratories, Murray Hill, NJ
uucp: {att,decvax,ucbvax}!ulysses!gsf       internet: gsf@ulysses.att.com