// 13.3 How does virtual function works in C++?

 #include <cstring>

 #include <iostream>

 using namespace std;

 class A {

 };

 class B {

 public:

     void f() {cout << "class B" << endl;};

 };

 class C {

 public:

     C();

 };

 class D {

 public:

     virtual void f() {

         cout << "class D" << endl;

     };

 };

 class E: public D {

 public:

     void f() {

         cout << "class E" << endl;

     };

 };

 int main()

 {

     D *ptr = new E();

     D d;

     E e;

     unsigned ui;

     cout << sizeof(A) << endl;

     cout << sizeof(B) << endl;

     cout << sizeof(C) << endl;

     cout << sizeof(D) << endl;

     cout << sizeof(E) << endl;

     // The result is 1 1 1 4 4 on Visual Studio 2012.

     ptr->f();

     // class with no data member have to occupy 1 byte, so as to have an address.

     // class with virtual functions need a pointer to the virtual function table.

     printf("The address of d is %p.\n", &d);

     printf("The address of e is %p.\n", &e);

     printf("The address of d.f is %p.\n", (&D::f));

     printf("The address of e.f is %p.\n", (&E::f));

     memcpy(&ui, &d, );

     printf("d = %X\n", ui);

     memcpy(&ui, &e, );

     printf("e = %X\n", ui);

     memcpy(&ui, ptr, );

     printf("*ptr = %X\n", ui);

     return ;

 }