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

All good answers above. One extra thing you should keep in mind - you can also have a pure virtual destructor. The only difference is that you still need to implement it.

Confused?

    --- header file ----
    class foo {
    public:
      foo() {;}
      virtual ~foo() = 0;

      virtual bool overrideMe() {return false;}
    };

    ---- source ----
    foo::~foo()
    {
    }

The main reason you'd want to do this is if you want to provide interface methods, as I have, but make overriding them optional.

To make the class an interface class requires a pure virtual method, but all of your virtual methods have default implementations, so the only method left to make pure virtual is the destructor.

Reimplementing a destructor in the derived class is no big deal at all - I always reimplement a destructor, virtual or not, in my derived classes.