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From: jbuck@epimass.UUCP
Newsgroups: comp.lang.c
Subject: Re: cpp macro expansion
Message-ID: <1062@epimass.UUCP>
Date: Fri, 17-Apr-87 21:47:41 EST
Article-I.D.: epimass.1062
Posted: Fri Apr 17 21:47:41 1987
Date-Received: Sat, 18-Apr-87 08:19:44 EST
References: <2857@linus.UUCP> <5764@brl-smoke.ARPA> <229@homxb.UUCP>
Reply-To: jbuck@epimass.UUCP (Joe Buck)
Organization: Entropic Processing, Inc., Cupertino, CA
Lines: 30
Keywords: cpp, #define, macro

In article <5764@brl-smoke.ARPA>, gwyn@brl-smoke.UUCP writes:
>> "token pasting".  People using the Reiser CPP (found on most
>> UNIX systems) typically resorted to the following trick:
>> 	#define GLUE(a,b) a/**/b
>> However, this is not guaranteed to work and, indeed, is
>> guaranteed NOT to work in X3J11-compliant compilers.  The
>> X3J11 invention for token pasting is:
>> 	#define GLUE(a,b) a ## b
>> You will probably not find many compilers implementing this
>> yet, since this part of the spec kept changing.

In article <229@homxb.UUCP> gemini@homxb.UUCP (Rick Richardson) writes:
>And we of course have a third method here at AT&T.  The
>preprocessor distributed with 4th generation make uses:
> 	#define GLUE(a,b) a\+b
>Can you say non-compliant?  I knew you could.

I use

#define QUOTE(x) x
#define GLUE(x,y) QUOTE(x)y

Well, it works for me, and it's prettier than a/**/b.  Can't tell
whether ANSI breaks this: I suppose a conforming compiler could
"tokenize" things before the preprocessor is invoked (or there
may be no separate preprocessor pass) -- but I like it.

-- 
- Joe Buck    {hplabs,ihnp4,sun,ames}!oliveb!epimass!jbuck
	      seismo!epiwrl!epimass!jbuck  {pesnta,tymix,apple}!epimass!jbuck