C++ Code Example: Data Abstraction – public, private, protected

In this code example, we explore data abstraction by utilizing public, private, and protected access specifiers within a Test class. This example highlights how these access levels control the visibility and accessibility of class members. The Test class contains three methods: privPrint (private), protPrint (protected), and pubPrint (public), each demonstrating their respective accessibilities.

In the main function, attempts to call privPrint and protPrint result in compilation errors, illustrating their restricted access, while pubPrint is successfully called, showcasing its public accessibility. This example effectively demonstrates the principles of data abstraction in C++.

#include <iostream>
using namespace std;

class Test {
    private:
        void privPrint() {
            cout << "I'm private" << endl;
        }
    public:
        void pubPrint() {
            cout << "I'm public" << endl;
        }
    protected:
        void protPrint() {
            cout << "I'm protected" << endl;
        }
};

int main() {
    Test t1;

    // error: 'privPrint' is a private member of 'Test'
    // t1.privPrint();
    // error: 'protPrint' is a protected member of 'Test'
    // t1.protPrint();
    // works
    t1.pubPrint();

    return 0;
}

Explanation

Defining the Test Class

Class Declaration

class Test {

The Test class is declared, encapsulating its member functions within different access specifiers.

Private Member Function

    private:
        void privPrint() {
            cout << "I'm private" << endl;
        }

The privPrint function is declared under the private access specifier, making it accessible only within the Test class itself. It prints the message “I’m private” to the console.

Public Member Function

    public:
        void pubPrint() {
            cout << "I'm public" << endl;
        }

The pubPrint function is declared under the public access specifier, making it accessible from outside the class. It prints the message “I’m public” to the console.

Protected Member Function

    protected:
        void protPrint() {
            cout << "I'm protected" << endl;
        }

The protPrint function is declared under the protected access specifier, making it accessible only within the Test class and its derived classes. It prints the message “I’m protected” to the console.

Main Function

Object Creation

int main() {
    Test t1;

Accessing Member Functions

Attempt to Access Private Function

    // error: 'privPrint' is a private member of 'Test'
    // t1.privPrint();

The commented-out line attempts to call privPrint(), which would result in a compilation error because privPrint is private and inaccessible outside the Test class.

Attempt to Access Protected Function

    // error: 'protPrint' is a protected member of 'Test'
    // t1.protPrint();

The commented-out line attempts to call protPrint(), which would also result in a compilation error because protPrint is protected and inaccessible outside the Test class.

Accessing Public Function

    // works
    t1.pubPrint();

The pubPrint function is called successfully, printing “I’m public” to the console because it is public and accessible from outside the class.

Summary of the Code

This C++ code demonstrates how access specifiers control the visibility of class members. It highlights that:

• Private members
  are accessible only within the class.
• Protected members
  are accessible within the class and its derived classes.
• Public members
  are accessible from anywhere.

Expected Output

The output of the code will be:

I'm public

This output confirms that only the public member function pubPrint is accessible from outside the Test class, successfully printing its message to the console.