function pointers member functions

It is always a good idea to do some research before asking a question. There were a couple of questions about member functions pointers in last few days and any of those answers would have been valuable for you.

Regarding a Zero check on pointers: The following sentence is so trivial that I am almost afraid to give that as an advice: It never hurts to check, but is also never a guarantee that a pointer is valid otherwise. You should make sure by other means (correct initialization) that your pointers (data pointer or member function pointers alike) have a valid value.

Of course, you can use the zero-value is indication that the member function pointer is not valid at the time, for example because no callback has been specified so far.