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From: flee@shire.cs.psu.edu (Felix Lee)
Newsgroups: comp.lang.c
Subject: Another pitfall.  Signed chars and ctype.h.
Message-ID: <Chsv$q2@cs.psu.edu>
Date: 7 Feb 90 22:15:50 GMT
Sender: news@cs.psu.edu (Usenet)
Organization: Penn State University Computer Science
Lines: 12

If you have "char * s;" you cannot say something like "isdigit(*s)" if
you want to be 8-bit clean.  "isdigit" etc. take an (int) in the range
[-1, UCHAR_MAX].

You have to say "isdigit((unsigned char) *s)".  Or you could declare
"unsigned char * s;" instead, but this is inconvenient since (char *)
isn't compatible with (unsigned char *).

This is only if your (char) is signed, but if you want to write
portably you shouldn't assume unsignedness of (char).
--
Felix Lee	flee@shire.cs.psu.edu	*!psuvax1!flee