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From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.lang.c
Subject: Re: #define CTRL(x) followup (it can't be done in ANSI C)
Message-ID: <1375@hoptoad.uucp>
Date: Mon, 1-Dec-86 23:33:13 EST
Article-I.D.: hoptoad.1375
Posted: Mon Dec  1 23:33:13 1986
Date-Received: Tue, 2-Dec-86 03:14:19 EST
References: <7136@elsie.UUCP> <779@valid.UUCP> <5396@brl-smoke.ARPA> <103@decvax.UUCP>
Organization: Nebula Consultants in San Francisco
Lines: 27

In article <103@decvax.UUCP>, minow@decvax.UUCP (Martin Minow) writes:
> As I understand the spec, Reiser constructions map into ANSI C as follows:
> 
> 		Reiser				ANSI
> token pasting:	#define foo(a,b) a/**/b		a##b
> string repl.:	#define foo(a) "xxx a yyy"	"xxx #a yyy"
> char repl.:	#define foo(a) 'a'		Not provided to my knowledge.
 
I believe this is wrong.  Try:

  string repl.:	#define foo(a) "xxx a yyy"	"xxx " #a " yyy"

There is still no way to do character replacement as in the Reiser CPP.
Some people have suggested
  char repl.:	#define foo(a) 'a'		(#a)[0]
but this is not a constant expression (as defined in section 3.4 of the
dpANS) so it cannot be used e.g. in a case label.  There was a kludge posted
that defined 52 new #define's (__a, __A, __b, __B, etc) but this is horrid
and does not support things like CTRL([).

It seems to me that the standards committee should support subscripting of
constant expressions (e.g. "["[0]) in constant expressions; that would
lay this issue to rest, finally.
-- 
John Gilmore  {sun,ptsfa,lll-crg,ihnp4}!hoptoad!gnu   jgilmore@lll-crg.arpa
    "I can't think of a better way for the War Dept to spend money than to
  subsidize the education of teenage system hackers by creating the Arpanet."