Public, Protected, and Private Inheritance in C++ Programming

Public, Protected and Private Inheritance in C++ Programming

In this tutorial, we will learn to use public, protected, and private inheritance in C++ with the help of examples.

In C++ inheritance, we can get a child class from the base class in various access modes. For instance,

class Base {
.... ... ....
};

class Derived : public Base {
.... ... ....
};

Notice the keyword public in the code

class Derived : public Base

This implies we have made a gotten class from the base class in public mode. On the other hand, we can likewise infer classes in protected or private modes.

These 3 keywords (public, protected, and private) are known as access specifiers in C++ inheritance.

---

public, protected, and private inheritance in C++

public, protected, and private inheritance have the following features:

• public inheritance makes public members of the base class public in the derived class, and the protected members of the base class remain protected in the derived class.
• protected inheritance makes the public and protected members of the base class protected in the derived class.
• private inheritance makes the public and protected members of the base class private in the derived class.

Note: private members of the base class are inaccessible to the derived class.

class Base {
    public:
        int x;
    protected:
        int y;
    private:
        int z;
};

class PublicDerived: public Base {
    // x is public
    // y is protected
    // z is not accessible from PublicDerived
};

class ProtectedDerived: protected Base {
    // x is protected
    // y is protected
    // z is not accessible from ProtectedDerived
};

class PrivateDerived: private Base {
    // x is private
    // y is private
    // z is not accessible from PrivateDerived
}

---

Example 1: C++ public Inheritance

// C++ program to demonstrate the working of public inheritance

#include <iostream>
using namespace std;

class Base {
   private:
    int pvt = 1;

   protected:
    int prot = 2;

   public:
    int pub = 3;

    // function to access private member
    int getPVT() {
        return pvt;
    }
};

class PublicDerived : public Base {
   public:
    // function to access protected member from Base
    int getProt() {
        return prot;
    }
};

int main() {
    PublicDerived object1;
    cout << "Private = " << object1.getPVT() << endl;
    cout << "Protected = " << object1.getProt() << endl;
    cout << "Public = " << object1.pub << endl;
    return 0;
}

Output

Private = 1
Protected = 2
Public = 3

Here, we have derived PublicDerived from Base in public mode.

As a result, in PublicDerived:

prot is inherited as protected.
pub and getPVT() are inherited as public.
pvt is inaccessible since it is private in Base.
Since private and protected members are not accessible, we need to create public functions getPVT() and getProt() to access them:

// Error: member "Base::pvt" is inaccessible
cout << "Private = " << object1.pvt;

// Error: member "Base::prot" is inaccessible
cout << "Protected = " << object1.prot;

---

Accessibility in Public Inheritance

Accessibility	private members	protected members	public members
Base Class	Yes	Yes	Yes
Derived Class	No	Yes	Yes

---

Example 2: C++ protected Inheritance

// C++ program to demonstrate the working of protected inheritance

#include <iostream>
using namespace std;

class Base {
   private:
    int pvt = 1;

   protected:
    int prot = 2;

   public:
    int pub = 3;

    // function to access private member
    int getPVT() {
        return pvt;
    }
};

class ProtectedDerived : protected Base {
   public:
    // function to access protected member from Base
    int getProt() {
        return prot;
    }

    // function to access public member from Base
    int getPub() {
        return pub;
    }
};

int main() {
    ProtectedDerived object1;
    cout << "Private cannot be accessed." << endl;
    cout << "Protected = " << object1.getProt() << endl;
    cout << "Public = " << object1.getPub() << endl;
    return 0;
}

Output

Private cannot be accessed.
Protected = 2
Public = 3

Here, we have derived ProtectedDerived from Base in protected mode.

As a result, in ProtectedDerived:

prot, pub and getPVT() are inherited as protected.
pvt is inaccessible since it is private in Base.
As we know, protected members cannot be accessed directly.

As a result, we cannot use getPVT() from ProtectedDerived. That is also why we need to create the getPub() function in ProtectedDerived in order to access the pub variable.

// Error: member "Base::getPVT()" is inaccessible
cout << "Private = " << object1.getPVT();

// Error: member "Base::pub" is inaccessible
cout << "Public = " << object1.pub;

---

Accessibility in Protected Inheritance

Accessibility	private members	protected members	public members
Base Class	Yes	Yes	Yes
Derived Class	No	Yes	Yes (inherited as protected variables)

---

Example 3: C++ private Inheritance

// C++ program to demonstrate the working of private inheritance

#include <iostream>
using namespace std;

class Base {
   private:
    int pvt = 1;

   protected:
    int prot = 2;

   public:
    int pub = 3;

    // function to access private member
    int getPVT() {
        return pvt;
    }
};

class PrivateDerived : private Base {
   public:
    // function to access protected member from Base
    int getProt() {
        return prot;
    }

    // function to access private member
    int getPub() {
        return pub;
    }
};

int main() {
    PrivateDerived object1;
    cout << "Private cannot be accessed." << endl;
    cout << "Protected = " << object1.getProt() << endl;
    cout << "Public = " << object1.getPub() << endl;
    return 0;
}

Output

Private cannot be accessed.
Protected = 2
Public = 3

Here, we have derived PrivateDerived from Base in private mode.

As a result, in PrivateDerived:

prot, pub and getPVT() are inherited as private.
pvt is inaccessible since it is private in Base.

As we probably am aware, private members can’t be gotten to straightforwardly.

Thus, we can’t use getPVT() from PrivateDerived. That is likewise why we have to make the getPub() work in PrivateDerived so as to get to the pub variable.

// Error: member "Base::getPVT()" is inaccessible
cout << "Private = " << object1.getPVT();

// Error: member "Base::pub" is inaccessible
cout << "Public = " << object1.pub;

---

Accessibility in Private Inheritance

Accessibility	private members	protected members	public members
Base Class	Yes	Yes	Yes
Derived Class	No	Yes (inherited as private variables)	Yes (inherited as private variables)

---

Thanks for watching! We hope you found this tutorial helpful and we would love to hear your feedback in the Comments section below. And show us what you’ve learned by sharing your photos and creative projects with us.