Public, Protected and Private Inheritance in C++ Programming

You can declare a derived class from a base class with different access control, i.e., public inheritance, protected inheritance or private inheritance.

#include <iostream>
using namespace std;

class base
{
.... ... ....
};

class derived : access_specifier base
{
.... ... ....
};

Note: Either public, protected or private keyword is used in place of access_specifier term used in the above code.

Example of public, protected and private inheritance in C++

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
}

In the above example, we observe the following things:

• base has three member variables: x, y and z which are public, protected and private member respectively.
• publicDerived inherits variables x and y as public and protected. z is not inherited as it is a private member variable of base.
• protectedDerived inherits variables x and y. Both variables become protected. z is not inherited
  If we derive a class derivedFromProtectedDerived from protectedDerived, variables x and y are also inherited to the derived class.
• privateDerived inherits variables x and y. Both variables become private. z is not inherited
  If we derive a class derivedFromPrivateDerived from privateDerived, variables x and y are not inherited because they are private variables of privateDerived.

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Accessibility in Public Inheritance

Accessibility	private variables	protected variables	public variables
Accessible from own class?	yes	yes	yes
Accessible from derived class?	no	yes	yes
Accessible from 2nd derived class?	no	yes	yes

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Accessibility in Protected Inheritance

Accessibility	private variables	protected variables	public variables
Accessible from own class?	yes	yes	yes
Accessible from derived class?	no	yes	yes (inherited as protected variables)
Accessible from 2nd derived class?	no	yes	yes

---

Accessibility in Private Inheritance

Accessibility	private variables	protected variables	public variables
Accessible from own class?	yes	yes	yes
Accessible from derived class?	no	yes (inherited as private variables)	yes (inherited as private variables)
Accessible from 2nd derived class?	no	no	no