C++ Inheritance

What is inheritance?

• Inheritance is a mechanism of reusing existing classes thereby allowing rapid development.
• A new class is created as a type of an existing class using the syntax "class <new-class> : public <existing-class1>, public <existing-class2>..." where "public" is an access specifier.
• The reused class is refered as base class and the new class is refered as derived class.
• A classes immediate base class is called "direct base class" and thier base classes are called "indirect base class".
• The order of object creation starts from the root to the most derived class.
• The order of object destruction is in reverse of object creation. Starts from the most derived class towards the root.
• 3 types of access specifiers are possible during inheritance.
• public: The public and protected members of the base class remain public and protected members of the derived class.
• protected: The public and protected members of the base class become protected members of the derived class.
• private: The public and protected members of the base class become private members of the derived class.

EXAMPLE: Demonstrate the basic functionality of inheritance

#include <iostream>

using namespace std;

// Base class
class Base {
    private:
        int data1;
    protected:
        int data2;
    public:
        Base(int d1, int d2) {
            data1 = d1;
            data2 = d2;
            cout << "Base constructor ..." << endl;
        }

        ~Base() {
            cout << "Base destructor ..." << endl;
        }
};

// Derived class1
class Derived1 : public Base {
    public:
        // Constructor Initialization
        Derived1(int d1, int d2) : Base(d1, d2) {
           cout << "Derived1 constructor ..." << endl;
        }

        void Print() {
            // cout << "data1=" << data1 << endl; ERROR: SINCE PRIVATE MEMBER
            cout << "data2=" << data2 << endl;
        }

        ~Derived1() {
           cout << "Derived1 destructor ..." << endl;
        }
};

// Derived class2
class Derived2 : private Base {
    public:
        // Constructor Initialization
        Derived2(int d1, int d2) : Base(d1, d2) {
           cout << "Derived2 constructor ..." << endl;
        }

        void Print() {
            // cout << "data1=" << data1 << endl; ERROR: SINCE PRIVATE MEMBER
            cout << "data2=" << data2 << endl;
        }

        ~Derived2() {
           cout << "Derived2 destructor ..." << endl;
        }
};

int main ()
{
    Derived1* d1 = new Derived1(10, 20);
    d1->Print();
    delete d1;

    Derived1* d2 = new Derived1(10, 30);
    d2->Print();
    delete d2;
}

OUTPUT:

Base constructor ...
Derived1 constructor ...
data2=20
Derived1 destructor ...
Base destructor ...
Base constructor ...
Derived1 constructor ...
data2=30
Derived1 destructor ...
Base destructor ...