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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: Comparing chars to constants
Message-ID: <9101@mimsy.UUCP>
Date: Mon, 26-Oct-87 01:48:14 EST
Article-I.D.: mimsy.9101
Posted: Mon Oct 26 01:48:14 1987
Date-Received: Wed, 28-Oct-87 02:51:57 EST
References: <4663@elroy.Jpl.Nasa.Gov> <2515@mmintl.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 32

In article <2515@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes:
>... I will note that one other way to write this, with the new ANSI
>standard, would be:
>
>	if (p == 0x80u)
>
>This will coerce p to unsigned.

 . . . which means that if p is a signed character, it will extend
from 0x80 == -128 to 0xff80 (assuming 16 bit int), and the comparison
will still always be false.

Incidentally, there is a bug in certain Sun compilers that causes

	char c = 0x80;
	if (c == (int)(char)0x80) ...

to fail.  Changing the code to

	if (c == (int)(char)(int)0x80) ...

makes the test succeed.  Curiously,

	char c = 0x80, d = 0x80;
	if (c == (int)(char)d) ...

succeeds without the extra (int) cast.

Chris
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris