How to define a general member function pointer

Question

I have created a Timer class that must call a callback method when the timer has expired. Currently I have it working with normal function pointers (they are declared as void (

Answer 1

I'm assuming an interface like this:

void Timer::register_callback( void(*callback)(void*user_data), void* user_data );

template
void wrap_method_callback( void* class_pointer )
{
   AnyClass*const self = reinterpret_cast(class_pointer);
   (self->*Func_Value)();
}

class A
{
public:
   void callback()
   { std::cout << m_i << std::endl; }
   int m_i;
};

int main ()
{
   Timer t;
   A a = { 10 };
   t.register_callback( &wrap_method_callback, &a );
}

I think a better solution would be to upgrade call you callback to either use boost::function or a homegrown version (like Kornel's answer). However this require real C++ developers to get involved, otherwise you are very likely to introduce bugs.

The advantage of my solution is that it is just one template function. Not a whole lot can go wrong. One disadvantage of my solution is it may slice your class with cast to void* and back. Be careful that only AnyClass* pointers are passes as void* to the callback registration.