Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!im4u!ut-sally!husc6!mit-eddie!ll-xn!ames!oliveb!epimass!csi!csib!jwhitnel
From: jwhitnel@csib.UUCP
Newsgroups: comp.lang.c
Subject: Re: Comparing chars to constants
Message-ID: <1261@csib.UUCP>
Date: Wed, 21-Oct-87 12:56:35 EDT
Article-I.D.: csib.1261
Posted: Wed Oct 21 12:56:35 1987
Date-Received: Sat, 24-Oct-87 21:21:57 EDT
References: <4663@elroy.Jpl.Nasa.Gov> <7373@alice.UUCP>
Reply-To: jwhitnel@csib.UUCP (Jerry Whitnell)
Organization: Communications Solutions Inc., San Jose, Ca
Lines: 33

In article <7373@alice.UUCP> ark@alice.UUCP writes:
|In article <4663@elroy.Jpl.Nasa.Gov>, david@elroy.UUCP writes:
|> From 6.6 both sides are converted into ints, 0x80 stays the
|> same but if p is equal to 0x80 it may always be sign extended on
|> some machines depending on its character sign convientions.
|
|(the original question had to do with the expression  c==0x80  where
| c is a character variable)
|
|Chars are indeed extended to ints for comparison, and that
|extension may or may not involve sign extension.  Saying
|
|	c == (char) 0x80
|
|may indeed be more portable, as one would hope 0x80 will be
|converted to a char and then undergo the same sign exension
|as c, but I wouldn't want to bet on the compiler getting it
|right.  Instead, consider making c an unsigned char or casting it:
|
|	((unsigned char) c) == 0x80
|
|(the outer parentheses are there for clarity)

If portability is of concern, some compilers don't support unsigned chars.
The preferred technique is 

    ( ( (int) c ) & 0xff ) == 0x80

The (int) cast can be left off.

Jerry Whitnell                           It's a damn poor mind that can only
Communication Solutions, Inc.            think of one way to spell a word.
						-- Andrew Jackson