Path: utzoo!utgpu!cunews!micor!latour!revcan!darren
From: darren@revcan.UUCP (Darren Morbey)
Newsgroups: comp.lang.c
Subject: Re: The nonexistent operator (along = v. == lines)
Summary: Clarification
Keywords: xor
Message-ID: <157@revcan.UUCP>
Date: 3 Apr 91 15:35:32 GMT
References: <156@revcan.UUCP>
Organization: Revenue Canada, Taxation; Office Communications Division
Lines: 20

Based on some of the responses I've gotten so far, I should
clarify what I would like when I say ^^.  I do realize that there
is no "short-circuit" evaluation (a term used repeatedly) for the
Boolean xor as there is for && and ||; I didn't realize that
short-circuit evaluation was the standard.

What I did require was an operator, macro, or function that treated
its operands as "zero" or "non-zero" as && and || do rather than
the bitwise & | ^.  I also would like some guarantee that both
operands were evaluated *once* *and* *only* *once* (O&OO).  Based
on that, I do recognize that in
  1.    #define XOR(a,b) ( ( !(a) && (b) ) || ( (a) && !(b) ) )
I cannot guarantee that a is evaluated O&OO every time.

As I mentioned, I would like to be as portable as possible, so
please be careful.

[ Darren Morby     +1 613 957 9281     {uunet|lsuc|fts1}!revcan!darren ]
[ Revenue Canada Taxation, 3052-400 Cumberland St, Ottawa,ONT  K1A 0L8 ]
[                            "The challenge... is yours."  Dick Clark. ]