C : is there "lazy evaluation" when using && operator, as in C++?

Question

I would like to know if this looks correct :

while((next !=NULL) && (strcmp(next->name, some_string) < 0) {
    //some process
}

I mean, if next is NULL, then the second part of the expression won't be ever tested by the compiler? I have heard that in C++ it's the case (but I'm not even sure of it).

Can someone confirm me that I won't get strange errors on some compilers with that?

Epiphenomenalism

@Sean: Testing doesn't necessarily equal "guaranteed by the standard". – Restless

Incidentally this not always true in C++. The expression: (next != NULL) may use an overloaded != operator on whatever type next is. That operator may return another type on which && is overloaded. And for overloaded && there is no built-in short-circuiting, so the expression on the RHS will be evaluated regardless of the LHS. – Gush

@pmg: Why is this not lazy evaluation? – Gallic

@codymanix: Lazy evaluation is about delaying computation until the point that the results are required. This is short-circuiting, to avoid undefined behaviour (like deferencing a null pointer). – Restless

Hmmm ... looks like some people call that short-circuiting lazy evaluation ( c2.com/cgi/wiki?LazyEvaluation ). I don't agree: to me lazy evaluation is "get ready to evaluate something but don't do it just now"; short-circuiting is "if it's ok do something right now, otherwise don't ever do it" – Larkspur

@oli: By your definition, short circuiting is lazy evaluation, too. Avoiding access to uninitialized values is just a side effect of it which is often used. – Gallic

@codymanix: I guess it's a matter of definition. I agree with pmg's definition... – Restless

Answer 1

Yes && is short circuited and you are using it correctly.
If next is NULL string compare will never happen.

Thundershower

Answer 2

Yes, in C++ short circuit and and or operators are available.

Here's a question answered in the C-faq on the subject.

Churrigueresque

Answer 3

It's definitely the case in both C and C++.

Sudatory

Correction: It's definitely true in C, so it should be true in C++. – Zhukov

@Zhukov - that's no correction. C++ and C are covered by standards, and this answer is correct about what both standards say (for built-in types in C++) – Gush

Answer 4

This will work with lazy evaluation (the second statement not evaluated if the first one is evaluated to "false") unless your compiler is so non-standard compliant it can't even be named a C compiler. Millions lines of code in the field rely on this behavior, so you can think that this behavior is just guaranted.

Lifelong

it's called short circuit evaluation, lazy evaluation is something else – Kuebbing