Sams Teach Yourself C++ in 24 Hours, fifth edition

Hour 18. Making Use of Advanced Polymorphism

What You’ll Learn in This Hour:

• What “casting down” is and why you might want to do it

• What abstract data types are

• What pure virtual functions are

Problems with Single Inheritance

In the previous hours, we discussed treating derived objects polymorphically with their base classes. You saw that if the base class has a member function speak() that is overridden in the derived class, a pointer to a base object that is assigned to a derived object will do the right thing. The Mammal12 program in Listing 18.1 illustrates this idea.

Listing 18.1 The Full Text of Mammal12.cpp

 1: #include <iostream> 2: 3: class Mammal 4: { 5: public: 6:     Mammal():age(1) { std::cout << "Mammal constructor ...\n"; ...