Performance penalty for working with interfaces in C++?

Question

Is there a runtime performance penalty when using interfaces (abstract base classes) in C++?

Answer 1

I don't think that the cost comparison is between virtual function call and a straight function call. If you are thinking about using a abstract base class (interface), then you have a situation where you want to perform one of several actions based of the dynamic type of an object. You have to make that choice somehow. One option is to use virtual functions. Another is a switch on the type of the object, either through RTTI (potentially expensive), or adding a type() method to the base class (potentially increasing memory use of each object). So the cost of the virtual function call should be compared to the cost of the alternative, not to the cost of doing nothing.