Question

Possible Duplicate:
What does void(U::*)(void) mean?

Considering the following:

template <class T>
class myButtoncb  {
   private:
      T *ptr;
      void (T::*cback) (void)
}

What I understand is:

void (*cback) (void)

Which is nothing but a function pointer that to a function that returns void, and takes no argument.

What I dont understand is, what is the importance of T::? Isn’t it enough to declare
only like void (*cback) (void) ?

Answer 1

This says that it’s a member function that has a this pointer. Otherwise, it would be a free function, wouldn’t have any idea what object it was operating on, and wouldn’t be able to access any non-static member functions or member variables.