Difference between Private and Protected in C++ with Example

Protected

Protected access modifier is similar to that of private access modifiers, the difference is that the class member declared as Protected are inaccessible outside the class but they can be accessed by any subclass(derived class) of that class.

Example:



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// C++ program to demonstrate
// protected access modifier
  
#include <bits/stdc++.h>
using namespace std;
  
// base class
class Parent {
  
    // protected data members
protected:
    int id_protected;
};
  
// sub class or derived class
class Child : public Parent {
  
public:
    void setId(int id)
    {
  
        // Child class is able to access the inherited
        // protected data members of the base class
  
        id_protected = id;
    }
  
    void displayId()
    {
        cout << "id_protected is: "
             << id_protected << endl;
    }
};
  
// main function
int main()
{
  
    Child obj1;
  
    // member function of the derived class can
    // access the protected data members of the base class
  
    obj1.setId(81);
    obj1.displayId();
    return 0;
}

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Output:

id_protected is: 81

Private

The class members declared as private can be accessed only by the functions inside the class. They are not allowed to be accessed directly by any object or function outside the class. Only the member functions or the friend functions are allowed to access the private data members of a class.

Example:

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// C++ program to demonstrate private
// access modifier
  
#include <iostream>
using namespace std;
  
class Circle {
  
    // private data member
private:
    double radius;
  
    // public member function
public:
    void compute_area(double r)
    {
        // member function can access private
        // data member radius
        radius = r;
  
        double area = 3.14 * radius * radius;
  
        cout << "Radius is: " << radius << endl;
        cout << "Area is: " << area;
    }
};
  
// main function
int main()
{
    // creating object of the class
    Circle obj;
  
    // trying to access private data member
    // directly outside the class
    obj.compute_area(1.5);
  
    return 0;
}

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Output:

Radius is: 1.5
Area is: 7.065

Difference between Private and Protected

Private Protected
The class members declared as private can be accessed only by the functions inside the class. Protected access modifier is similar to that of private access modifiers.
Only the member functions or the friend functions are allowed to access the private data members of a class. The class member declared as Protected are inaccessible outside the class but they can be accessed by any subclass(derived class) of that class.


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