Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!apple!uokmax!munnari.oz.au!cluster!metro!natmlab.dap.csiro.au!ditsyda!evans
From: evans@ditsyda.oz (Bruce Evans)
Newsgroups: comp.lang.c
Subject: Re: isascii (was: Another pitfall.  Signed chars and ctype.h)
Message-ID: <2448@ditsyda.oz>
Date: 15 Feb 90 05:02:14 GMT
References: <Cuunry2@cs.psu.edu> <1990Feb12.043324.5259@sq.sq.com>
Reply-To: evans@ditsyda.oz (Bruce Evans)
Organization: CSIRO DIT Sydney, Australia
Lines: 21

In article <1990Feb12.043324.5259@sq.sq.com> msb@sq.com (Mark Brader) writes:
*If the code has to run on ANSI and non-ANSI C's, I'd prefer:
*
*	#include <stdio.h>
*	#include <ctype.h>
*
*	#ifndef isascii		/* oh, must be ANSI C */
*	#define isascii(x) (((x) >= 0 && (x) < UCHAR_MAX) || (x) == EOF))
*	#endif
*
*and then
*	isascii(*s) && isdigit(*s)

Why doesn't ANSI C guarantee isdigit() (etc.) on *all* characters? The usual
implementation would be to move the base of the ctype array from -1
(EOF) back to -128 (SCHAR_MIN).

Then you can define isascii(x) to be 1 in the above, and not have to worry
about side affects. You still have to watch out for isdigit() on non-chars.
-- 
Bruce Evans		evans@ditsyda.oz.au