How do you declare an interface in C++?

Question

How do I setup a class that represents an interface? Is this just an abstract base class?

Answer 1

If you're using Microsoft's C++ compiler, then you could do the following:

struct __declspec(novtable) IFoo
{
    virtual void Bar() = 0;
};

class Child : public IFoo
{
public:
    virtual void Bar() override { /* Do Something */ }
}

I like this approach because it results in a lot smaller interface code and the generated code size can be significantly smaller. The use of novtable removes all reference to the vtable pointer in that class, so you can never instantiate it directly. See the documentation here - novtable.