What is a virtual function?

A virtual function is a method, which is used to replace the implementation provided by the base class. The said replacement is always called whenever the object in question is actually of the derived class, even if a base pointer instead of a derived pointer accesses the object. Virtual functions are always used with inheritance, and they are called according to the type of the object pointed or referred, not according to the type of pointer or reference. In other words, virtual functions are resolved later than usual, at runtime. The keyword virtual is used to make a method virtual.