C++ zyBooks Chapter 5 - Inheritance

The term derived class (or subclass) refers to a class that is derived from another class that is known as a base class (or superclass).

Any class may serve as a base class; no changes to the definition of that class are required.

The derived class is said to inherit the properties of its base class, a concept commonly called inheritance.

An object declared of a derived class type has access to all the public members of the derived class as well as the public members of the base class.

class GenericItem {
public:
...
   void PrintItem() {
      cout << itemName << " " << itemQuantity << endl;
   };

protected:
   string itemName;
   int itemQuantity;
};

class ProduceItem : public GenericItem { // Derived from GenericItem
public:
...
   void PrintItem() {
      cout << itemName << " " << itemQuantity
      << " (Expires: " << expirationDate << ")"
      << endl;
   };

private:
   string expirationDate;
};

Function overloading is a form of compile-time polymorphism wherein the compiler determines which of several identically-named functions to call based on the function's arguments.

Another form is runtime polymorphism wherein the compiler cannot make the determination but instead the determination is made while the program is running.

When the object is a pointer, the indication of virtual causes the program to dynamically determine the correct function to call based on the pointer type.

z5.4-virtual.cc - runtime polymorphism via a virtual function - compare with and without virtual

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In contrast, one can create a truly virtual function, known as a pure virtual function, using the following syntax:

  class GenericItem {
        ...
        virtual void PrintItem() = 0;
        ...
  };

The function must be defined and implemented in a derived class.