How can I simulate interfaces in C++?

Question

Since C++ lacks the interface feature of Java and C#, what is the preferred way to simulate interfaces in C++ classes? My guess would be multiple inheritance o

Answer 1

If you don't use virtual inheritance, the overhead should be no worse than regular inheritance with at least one virtual function. Each abstract class inheritted from will add a pointer to each object.

However, if you do something like the Empty Base Class Optimization, you can minimize that:

struct A
{
    void func1() = 0;
};

struct B: A
{
    void func2() = 0;
};

struct C: B
{
    int i;
};

The size of C will be two words.