Date: Sun, 1 Feb 1998 14:14:10 -0500 (EST)
Message-Id: <199802011914.OAA20468@delorie.com>
From: DJ Delorie <dj AT delorie DOT com>
To: eliz AT is DOT elta DOT co DOT il
CC: Vik DOT Heyndrickx AT rug DOT ac DOT be, djgpp-workers AT delorie DOT com
In-reply-to: <Pine.SUN.3.91.980201195130.16390L-100000@is> (message from Eli
	Zaretskii on Sun, 1 Feb 1998 19:51:48 +0200 (IST))
Subject: Re: char != unsigned char... sometimes, sigh
Precedence: bulk


>   #define isalnum(c) (__dj_ctype_flags[((c)&0xff)+1] & __dj_ISALNUM)
> 
> That "+1" is designed to make EOF be 0, and the zeroth element of
> __dj_ctype_flags[] array should be set appropriately.  Doesn't this
> work?

Given -1, you end up with (-1 & 0xff) + 1, which is 256.  You get the
same results for 0xff.  Unfortunately, you can't tell the difference
between -1 meaning EOF and -1 meaning signed character 0xff
sign-extended and stored in a signed int variable (0xffffffff).