This is a good time to remind that the time when pointers was initialized to 0 should now been seen as a time past, if possible.
In the new standard, all pointers should be initialized to nullptr, provided your compiler supports it (GCC and MSVC does).
So avoid using 0 or NULL unless a) your compiler doesn't support it or b) you are using legacy code.
Using 0 for pointers is an Evil™ thing that defeats the type system.