Question

I have a class which is to listen to mouse events. However, I do not want to force the user to implement any specific one, but I do want to make it clear that they must inherit it.

Is there a way to do this?

Thanks

Answer 1

You can declare a pure virtual destructor, but give it a definition. The class will be abstract, but any inheriting classes will not by default be abstract.

struct Abstract
{
     virtual ~Abstract() = 0;
};

Abstract::~Abstract() {}

struct Valid: public Abstract
{
        // Notice you don't need to actually overide the base
        // classes pure virtual method as it has a default
};


int main()
{
    // Abstract        a;  // This line fails to compile as Abstract is abstract
    Valid           v;  // This compiles fine.
}