C++ Multiple Inheritance

C++ supports multiple inheritance, multilevel inheritance and hierarchical inheritance, which are the different forms of multiple inheritance in C++ programming language.

• Multiple Inheritance: In multiple inheritance, a class is derived from more than one base class. This allows a class to inherit the properties and methods of multiple classes.


• Multilevel Inheritance: In multilevel inheritance, a class is derived from a class that is derived from another class. It allows you to create a hierarchy of classes where each class is a subclass of another class.


• Hierarchical Inheritance: In hierarchical inheritance, a class is derived from multiple classes, but each class is not derived from the same class. Instead, each class is derived from a different base class.

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Multiple Inheritance

Multiple inheritance is a feature of object-oriented programming language in which an object or class can inherit characteristics and features from more than one parent class. In other words, it is a situation where a single class is derived from more than one base class. The class which is derived from multiple base classes is known as the derived class or the sub class.

Example:
Consider the following class structures to demonstrate multiple inheritance.

#include <iostream>

using namespace std;

class Base1 {
    public:
        int publicData1;
};

class Base2 {
    public:
        int publicData2;
};

class Derived: public Base1, public Base2 {
};

int main() {
    Derived d;
    d.publicData1 = 10;
    d.publicData2 = 20;
    cout << "Public Data1: " << d.publicData1 << endl;
    cout << "Public Data2: " << d.publicData2 << endl;
    return 0;
}

Output

Public Data1: 10
Public Data2: 20

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Multilevel Inheritance

In multilevel inheritance, a derived class becomes the base class for another derived class. This allows for a hierarchical inheritance structure. The syntax is similar to single and multiple inheritance.

Here is an example of multilevel inheritance in C++:

#include <iostream>
using namespace std;

class Base {
  public:
    int baseVariable;
};

class Derived1 : public Base {
  public:
    int derived1Variable;
};

class Derived2 : public Derived1 {
  public:
    int derived2Variable;
};

int main() {
  Derived2 derived2Object;
  derived2Object.baseVariable = 10;
  derived2Object.derived1Variable = 20;
  derived2Object.derived2Variable = 30;

  cout << "Base Variable: " << derived2Object.baseVariable << endl;
  cout << "Derived1 Variable: " << derived2Object.derived1Variable << endl;
  cout << "Derived2 Variable: " << derived2Object.derived2Variable << endl;

  return 0;
}

Output

Base Variable: 10
Derived1 Variable: 20
Derived2 Variable: 30

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Hierarchical Inheritance

In hierarchical inheritance, multiple derived classes inherit from a single base class. This allows for a clean and organized inheritance structure. The syntax is similar to single and multiple inheritance.

#include <iostream>
using namespace std;

class Base {
    public:
        int baseValue;
        Base() {}
        Base(int baseValue) {
            this->baseValue = baseValue;
        }
};

class Derived1: public Base {
    public:
        int derived1Value;
        Derived1() {}
        Derived1(int baseValue, int derived1Value): Base(baseValue) {
            this->derived1Value = derived1Value;
        }
};

class Derived2: public Base {
    public:
        int derived2Value;
        Derived2() {}
        Derived2(int baseValue, int derived2Value): Base(baseValue) {
            this->derived2Value = derived2Value;
        }
};

int main() {
    Derived1 d1(10, 20);
    Derived2 d2(30, 40);
    cout << "Derived1's baseValue: " << d1.baseValue << endl;
    cout << "Derived1's derived1Value: " << d1.derived1Value << endl;
    cout << "Derived2's baseValue: " << d2.baseValue << endl;
    cout << "Derived2's derived2Value: " << d2.derived2Value << endl;
    return 0;
}

Output

Derived1's baseValue: 10
Derived1's derived1Value: 20
Derived2's baseValue: 30
Derived2's derived2Value: 40

In this example, the class Base is the base class, Derived1 and Derived2 are the derived classes and both the derived classes inherit the baseValue from the base class Base.