What is a constant expression

[David Goodenough]

>From article <1219 at crdos1.crd.ge.COM>, by davidsen at crdos1.crd.ge.COM (Wm E Davidsen Jr):
>   Background: large program, defines ASCII control characters with a
> macro as follows:
> 	#define CNTL(c) ('c' & 037)
> While this work fine with pcc, the ANSI preprocessor doesn't expand it.

This is:

1. Grotesque,

2. Workable.

Flame away if you wish, just try it first.

#define	prequote(x) 'x
#define postquote(x) x'

#define	CNTL(c) ((postquote(prequote(c))) & 0x1f)

CNTL(c)

Bletch :-/

MAJOR MAJOR PROBLEM - our C compiler (greenhills) likes the useages of
postquote and prequote in that order. Some compilers may not care, while
others might want them reversed. I think it depends on whether nested
macros are expanded from the inside out (as Greenhills does), or outside
in.

It's probably not portable .... Oh well.
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