Re: Virtual function pointers == NULL. Allowed?

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 1 Oct 2008 18:33:56 CST

Message-ID:

<MOSEk.162629$FR.449164@twister1.libero.it>

Daniel T. ha scritto:

#include <cassert>
class Foo {
public:
         virtual void fnA() = 0;
         virtual void fnB() = 0;
};

int main() {
         assert( &Foo::fnB );
         assert( &Foo::fnA );
}

What does the standard say about the above code? In the compiler I'm
using now, the first assert will not fire, but the second one will. I
expected that neither assert would fire...

Then your compiler is very buggy. According to 4.12:

"[... a] null member pointer value is converted to false; any other
value is converted to true."

The null member pointer value is defined in 4.11 and is a value which is
"distinguishable from any pointer to member not created from a null
pointer constant".

So neither &Foo::fnA nor &Foo::fnB are null member pointer values and
therefore none of them, when converted to bool, shall evaluate to false.

HTH,

Ganesh

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