Virtual functions in C++

The key implementation in Stroustrup’s C with classes (C++ early form) was that the set of virtual functions in a class defines an array of pointers to functions so that the call of a virtual function is simply an indirect function call through that array.

class A
{
    int a;
public:
    virtual void f();   
    virtual void g(int);
    virtual void h(double);   
};

class B : public A
{
public:
    int b;
    void g(int); //overrides A::g()
    virtual void m(B*);
};

class  B is derived from class A and class A is the base class of class A