Are C++ zero (null) pointers supposed to return false?

Question

I'm not sure if my understanding of C++ is wrong.. I've read that 1) all non-zero values are equivalent to TRUE, and zero is equivalent to FALSE; 2) null pointers are stored as zero.

Yet code like this:

void ViewCell::swapTiles (ViewCell *vc) {
    ViewTile *tmp = vc->tile();
    [stuff ...]
    if (tmp) addTile(tmp);
}

Gives me a segfault from dereferencing a null pointer, but

if (tmp != 0) addTile(tmp);

works fine. Any idea why?

Answer 1

For a pointer, p and (p != 0) are exactly equivalent. If it gives you a segfault, then either it's not a plain pointer, or the problem is elsewhere

Answer 2

C++ 0 pointers are not necessarily stored as an all zero bit pattern, but the token 0 is always interpreted as the 0 pointer if the compiler thinks it's a pointer, and the integer 0 is always coerced to the 0 pointer (with possibly a different bit pattern) if the compiler thinks it's an integer that needs to be type converted. And pointers to different things can have different sizeof, which can also be a different sizeof than integers. But you can see how it all works out. Usually. Clear?