Function Overriding in C++: (Function Overloading vs. Overriding)

C++ Function Overriding: An Overview

What is Function Overriding in C++?

The function call by the object of the derived class invokes the derived class method instead of the base class. Thus, the derived class method overrides the base class method. Hence,

• The function in the derived class becomes the overriding function
• The function in the base class becomes the overridden function

From here onwards, we will use the termsoverriding and overridden method to refer to the same methods of derived class and base class respectively.

Syntax

class Parent{

 access_modifier:

 // overridden function
 return_type name_of_the_function(){}

 };

}

 class child : public Parent {

 access_modifier:

 // overriding function
 return_type name_of_the_function(){}

 };

 }

Example in C++ Online Compiler

#include <iostream>
using namespace std;

class DotNetTricks { 
public:
 void print() { //overridden function
 cout << "Welcome to DotNetTricks" << endl;
 }
};

class ScholarHat : public DotNetTricks {
public:
 void print() { //overriding function
 cout << "Welcome to ScholarHat" << endl;
 }
};

int main() {
 ScholarHat obj1;

 // Call the print() function of the ScholarHat class
 obj1.print();

 return 0;
}

Output

Welcome to ScholarHat

We have already seen this illustration in the previous tutorial while studying the runtime polymorphism in C++. Here, what if we call the print() function from an object of the DotNetTricks class? If we do so, the print() function will not get overridden because the object of the base class will always invoke the method of the base class and not the derived class.

Make sure that you are thorough with the concepts of pointers in C++, functions in C++, Call by Value and Call by Reference in C++, and the OOPs concepts in C++. If not; go back, refer them, and then come here.

Read More - C++ Interview Interview Questions and Answers

Variations in C++ Function Overriding

• Call Overridden Function From Derived Class

Example

#include <iostream>
using namespace std;

class DotNetTricks {
public:
 void print() { // overridden function
 cout << "Welcome to DotNetTricks" << endl;
 }
};

class ScholarHat : public DotNetTricks {
public:
 void print() { // overriding function
 cout << "Welcome to ScholarHat" << endl;
 DotNetTricks::print(); // call overridden function
 }
};

int main() {
 ScholarHat obj1;
 obj1.print();

 return 0;
}

In this program, we have called the overridden function inside the derived class, ScholarHat itself. When you call obj1.print(), it first executes the overridden print() method in the ScholarHat class and then explicitly calls the overridden function from the base class using DotNetTricks::print(). Thus, we can use the scope resolution operator :: to access the overridden function of the base class.

Output

Welcome to ScholarHat
Welcome to DotNetTricks

• Access Overridden Function to the Base Class

Example

#include <iostream>
using namespace std;

class DotNetTricks {
public:
 void print() { // overridden function
 cout << "Welcome to DotNetTricks" << endl;
 }
};

class ScholarHat : public DotNetTricks {
public:
 void print() { // overriding function
 cout << "Welcome to ScholarHat" << endl;
 }
};

int main() {
 ScholarHat obj1, obj2;
 obj1.print();

 // Access the print() function of the Base class
 obj2.DotNetTricks::print();

 return 0;
}

In the above C++ code, we have created two ScholarHat objects, obj1 and obj2. obj1.print() calls the overridden print() function in the ScholarHat class, while obj2.DotNetTricks::print() explicitly accesses and calls the print() function of the DotNetTricks base class in the main() function.

Output

Welcome to ScholarHat
Welcome to DotNetTricks

• Call Overridden Function Using Pointer

Example in C++ Compiler

#include <iostream>
using namespace std;

class DotNetTricks {
public:
 void print() { //overridden function
 cout << "Welcome to DotNetTricks" << endl;
 }
};

class ScholarHat : public DotNetTricks {
public:
 void print() { // overriding function
 cout << "Welcome to ScholarHat" << endl;
 }
};

int main() {
 ScholarHat sobj1;

 // Pointer of the DotNetTricks type that points to sobj1
 DotNetTricks* ptr = &sobj1;

 // Calls the function of DotNetTricks using ptr
 ptr->print();

 return 0;
}

• In the above code, a pointer of DotNetTricks type named ptr points to the ScholarHat object sobj1
• When we call the print() function using ptr, it calls the overridden function and not the overriding function.
• The reason is even though ptr points to a ScholarHat object, it is actually of DotNetTricks type. So, it calls the member function of the DotNetTricks class.
• Thus, the print() function of the derived class, ScholarHat is not overriding the print() of the base class, DotNetTricks
• Here comes the need for virtual functions in the base class which we will see in the next tutorial, C++ Virtual Functions.

Output

Welcome to DotNetTricks

Function Overloading Vs Function Overriding

Summary