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From: drw@cullvax.UUCP (Dale Worley)
Newsgroups: comp.sources.d
Subject: ANSI C preproccessor concatenate
Message-ID: <1449@cullvax.UUCP>
Date: Tue, 11-Aug-87 14:17:51 EDT
Article-I.D.: cullvax.1449
Posted: Tue Aug 11 14:17:51 1987
Date-Received: Thu, 13-Aug-87 04:45:25 EDT
Organization: Cullinet Software, Westwood, MA, USA
Lines: 31

allbery@ncoast.UUCP (Brandon S. Allbery) writes:
- The reason for this is that I have a cpp macro which provides function proto-
- types under ANSI C and omits them for old-fashioned C.  Example:
- 
- 	DEFUN(extern generic malloc, (unsigned));
- 
- becomes
- 
- 	extern generic malloc(unsigned);

[Under ANSI C he writes:]

- #define DEFUN(fn,proto)		fn##proto
- 
- It assumes that X3J11 is #defined by ANSI C (wrong, I'm certain) and that the
- concatenation operator is ## (I think this is right).  (Purists would argue
- that ## isn't needed; but I have a thing about "xx (yy)" as a function defi-
- nition; I want to search for functions with "xx(" and C control structures
- (if, while, switch) with "xx (".)

You'll lose big if you try this!  The reason is that the ## operator
concatenates the character representation of the two surrounding
tokens to form what must be the character representation of a token.
Calling DEFUN(func,(a,b)) tries to concatenate the two tokens "func"
and "(", which together don't form a token.

Dale
-- 
Dale Worley	Cullinet Software		ARPA: cullvax!drw@eddie.mit.edu
UUCP: ...!seismo!harvard!mit-eddie!cullvax!drw
OS/2: Yesterday's software tomorrow	    Nuclear war?  There goes my career!