C++ Programming Tutorials

Understanding Inheritance in C++

Inheritance is a fundamental concept in object-oriented programming that allows a new class, known as the derived class, to inherit attributes and behaviors (methods) from an existing class, called the base class. This promotes code reusability and establishes a natural hierarchy between classes.

Types of Inheritance in C++

1. Single Inheritance

Definition: A derived class inherits from a single base class.

#include <iostream>
using namespace std;

class Base {
public:
    void show() { cout << "Base class" << endl; }
};

class Derived : public Base {
public:
    void display() { cout << "Derived class" << endl; }
};

int main() {
    Derived d;
    d.show();     // Inherited from Base
    d.display();  // Defined in Derived
    return 0;
}

Characteristics: Simple and straightforward, used to extend a single base class.

2. Multiple Inheritance

Definition: A derived class inherits from more than one base class.

#include <iostream>
using namespace std;

class Base1 {
public:
    void show() { cout << "Base1" << endl; }
};

class Base2 {
public:
    void display() { cout << "Base2" << endl; }
};

class Derived : public Base1, public Base2 {
public:
    void showAll() { show(); display(); }
};

int main() {
    Derived d;
    d.showAll();  // Calls methods from both Base1 and Base2
    return 0;
}

Characteristics: Allows combining functionality from multiple classes, but can lead to ambiguity if multiple base classes have methods with the same name.

3. Multilevel Inheritance

Definition: A derived class inherits from another derived class.

#include <iostream>
using namespace std;

class Base {
public:
    void show() { cout << "Base" << endl; }
};

class Intermediate : public Base {
public:
    void display() { cout << "Intermediate" << endl; }
};

class Derived : public Intermediate {
public:
    void showAll() { show(); display(); }
};

int main() {
    Derived d;
    d.showAll();  // Calls methods from Base and Intermediate
    return 0;
}

Characteristics: Creates a hierarchy of classes, where each level extends the previous one.

4. Hierarchical Inheritance

Definition: Multiple derived classes inherit from a single base class.

#include <iostream>
using namespace std;

class Base {
public:
    void show() { cout << "Base" << endl; }
};

class Derived1 : public Base {
public:
    void display1() { cout << "Derived1" << endl; }
};

class Derived2 : public Base {
public:
    void display2() { cout << "Derived2" << endl; }
};

int main() {
    Derived1 d1;
    Derived2 d2;
    d1.show();    // Base class method
    d2.show();    // Base class method
    return 0;
}

Characteristics: Allows different derived classes to use the same base class methods and properties.

5. Hybrid Inheritance

Definition: A combination of two or more types of inheritance.

#include <iostream>
using namespace std;

class Base1 {
public:
    void show1() { cout << "Base1" << endl; }
};

class Base2 {
public:
    void show2() { cout << "Base2" << endl; }
};

class Intermediate : public Base1, public Base2 {
public:
    void showAll() { show1(); show2(); }
};

class Derived : public Intermediate {
public:
    void display() { showAll(); }
};

int main() {
    Derived d;
    d.display();  // Calls methods from Base1 and Base2 via Intermediate
    return 0;
}

Characteristics: Combines multiple types of inheritance, potentially introducing complexity and ambiguity.

6. Protected Inheritance

Definition: Inherits from a base class with protected access specifier.

#include <iostream>
using namespace std;

class Base {
public:
    void show() { cout << "Base" << endl; }
};

class Derived : protected Base {
public:
    void display() { show(); }
};

int main() {
    Derived d;
    d.display();  // OK, shows "Base"
    // d.show();  // Error, show() is protected in Derived
    return 0;
}

Characteristics: Base class members become protected in the derived class, not accessible from outside the derived class.

Function Overriding in C++

Definition: Function overriding is a feature in C++ that allows a derived class to provide a specific implementation of a function that is already defined in its base class. The function in the base class is called a "virtual function" and the function in the derived class is said to "override" the base class function.

Key Points:

The base class function must be declared with the keyword virtual.
The derived class function should have the same signature as the base class function.
Function overriding enables polymorphism, where the base class pointer or reference can invoke derived class methods.

Example of Function Overriding

#include <iostream>
using namespace std;

class Base {
public:
    virtual void show() { cout << "Base class show()" << endl; }
};

class Derived : public Base {
public:
    void show() override { cout << "Derived class show()" << endl; }
};

int main() {
    Base* b;
    Derived d;
    b = &d;

    b->show();  // Calls Derived's show() due to function overriding

    return 0;
}

Explanation: In this example, the base class Base has a virtual function show(). The derived class Derived overrides this function. When the show() method is called through a base class pointer that points to a derived class object, the derived class's implementation is executed.

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