Path: utzoo!utgpu!water!watmath!clyde!rutgers!gatech!bloom-beacon!tut.cis.ohio-state.edu!uwmcsd1!ig!agate!ucbvax!hoptoad!gnu
From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.lang.c
Subject: Macro parameters getting substituted into strings
Message-ID: <4253@hoptoad.uucp>
Date: 27 Mar 88 13:26:00 GMT
References: <11879@brl-adm.ARPA> <4099@hoptoad.uucp> <7309@brl-smoke.ARPA> <983@mcgill-vision.UUCP>
Organization: Grasshopper Group in San Francisco
Lines: 36

I am not saying that I like the idea of macro parameter names being
replaced even inside strings.  My complaint is that an ANSI C compiler
does not have a capability that Unix C compilers have, and which many
Unix programs depend upon.  This is the capability to turn a single-
character argument into a character constant.  MOVING TO ANSI C REQUIRES
CHANGING ALL THE **USES**, AS WELL AS ALL THE **DEFINITIONS**, OF MACROS
THAT NEED THIS CAPABILITY!

In the BSD sources, Keith Bostic and I had to change more than 50 files
to deal with this.  The CPP on my binary A/UX, supposedly a System V,
replaces macro parameters inside strings.  I would like someone who has
System V sources to grep the sources for the CTRL macro -- I bet you
will find it there, using this technique.  If it's there, this ANSI
change is a "Quiet Change" to the compilers of both major Unix variants
(effectively, to ALL Unix implementations) and breaks dozens of the
application programs in both variants.  Can you say "Codifying existing
practice", boyz and goils?

My preferred way to fix this would be for ANSI C to allow the *
(indirection) and [] (subscripting) operators on string literals in
constant expressions.  Then the new ANSI "#" operator can be used to
create a character string, and * or [] can pull a character out of it,
all in a constant expression, e.g.:

#define CTRL(x) (# x [0]&0x1F)
...
	case CTRL(q):		turns to:	case ("q"[0]&0x1F):

I noticed that integer constant expressions are permitted to contain
subscripting in the new ANSI draft (Jan 88), but they aren't allowed to
contain string literals!  Inserting "string literals, " in lines 25
and 35 on page 56, and adding "except the values of string literals"
at the end of line 1 of page 57, would fix this.
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		"Watch me change my world..." -- Liquid Theatre