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From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: cpp macro expansion
Message-ID: <5764@brl-smoke.ARPA>
Date: Thu, 16-Apr-87 09:10:40 EST
Article-I.D.: brl-smok.5764
Posted: Thu Apr 16 09:10:40 1987
Date-Received: Sun, 19-Apr-87 05:47:00 EST
References: <2857@linus.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 15
Keywords: cpp, #define, macro

In article <2857@linus.UUCP> ms@security.uucp (Mistress Account) writes:
>The intent of the developers was that when cpp expands the code, the two
>macro arguments would be concatenated together into one token for the
>compiler, i.e:	MACRO(holy,cow) yields (holy_cow).

Unfortunately C a la K&R did not provide any way to do such
"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.