the logical xor operator!

[Karl Heuer]

Let's leave the political discussions in a different newsgroup, okay?

In article <1312 at ark.cs.vu.nl> maart at cs.vu.nl (Maarten Litmaath) writes:
>Karl W. Z. Heuer writes:
>>"Why wasn't logical xor added to ANSI C?".  The answer is that it isn't
>>useful enough to be worth the change to the language.
>
>Well, it's strange K&R didn't think of it in the first place...

"Why didn't K&R make a logical xor operator?" is a different question.  I'll
be glad to take this up in comp.lang.c after I return from vacation.

>Furthermore, it can be implemented WITHOUT breaking existing code,

This (or a weakened form of it) is a necessary condition for ANSI acceptance,
but it is not sufficient.

>and (admittedly) sometimes one would wish for ^^; but then again: isn't Karl
>having problems himself to get \c accepted by ANSI? :-)

It's hard to get anything new accepted by X3J11.  This is as it should be.

Do you want this operator just for completeness, or do you think you'd
actually use it a lot?  I can only think of one routine I've ever written in
which I've needed a logical xor, and since both operands were boolean I simply
used "^".

>>(and I hold the opinion that nothing else [but a normalized boolean] should
>>be handed to a logical operator)
>
>Come on Karl, what's so terrible about the following common practice?
>	if (some_pointer && ...) { ... }

Well, since you asked: The problem with it is that, by looking at this code
fragment in isolation, it's not obvious that some_pointer is a pointer, rather
than an integer, a character, a real, or a boolean.  If you explicitly write
	if (p != NULL && i != 0 && c != '\0' && r != 0.0 && b) { ... }
the reader has more information, which often makes the code more readable.

As I said, this is my personal opinion; I certainly don't think that the
language should be changed to enforce it.

Karl W. Z. Heuer (ima!haddock!karl or karl at haddock.isc.com), The Walking Lint