C++ Operator Overloading

overloaded functions

operators

unary operators

What is operator overloading and why we need it?

operator overloading

Operator overloading

special meaning or redefinition

unary or binary

user-defined

built-in

For example, we could negate a value of built-in data type int variable by just using the unary minus - operator with it.

int a = 10;
a = -a;

And, C++ uses the concept of operator overloading which allows us to use unary minus - operator with an object of user-defined data-type to negate its value, just like we could do with built-in data-type variables.

ob1 = -ob1;

where, ob1 is an object of a class and unary minus operator - is overloaded in a way that we could just simply apply the unary minus - operator on the objects of class, in the same manner as we apply unary minus - operator on any variables of built-in data-types to negate its value.

Without the concept of operator overloading, you wouldn't be able to work with the objects of a user-defined data type, the way you would work with built-in type variables and unary or binary operators.

How to achieve unary operator overloading?

Unary operator overloading can be achieved through an operator overloading member function.
An overloaded operator member function should be declared in the public section of a class.

Note:

user-defined

Overloading unary minus operator -

// C++ Overloading unary minus(-) operator


#include<iostream>

using namespace std;

class A
{
private:
int a;

public:
void set_a();
void get_a();
void operator -();
};


//Definition of set_a() function
void A :: set_a()
{
	a = 10;
}


//Definition of get_a() function
void A :: get_a()
{
	cout<< a <<"\n";
}


//Definition of overloaded unary minus operator - function
void A :: operator -()
{
	a = -a;
}


int main()
{
	A ob;
	ob.set_a();

	cout<<"The value of a is : ";
	ob.get_a();

	//Calling operator overloaded function - to negate the value
	-ob;

	cout<<"The value of a after calling operator overloading function - is : ";
	ob.get_a();
}

Output

The value of a is : 10
The value of a after calling operator overloading function - is : -10

Program Analysis

negate the value

user-defined

built-in

Overloading unary NOT operator !

As you know, the NOT ! operator when applied to any built-in type variable such as int will inverse its value from 0 to 1 or from 1 to 0 to represent a boolean value. But can we even negate the value in an object by using the unary NOT ! operator?

Yes, we can! Let us see how to overload the NOT ! operator -

// C++ Overloading unary NOT(!) operator


#include<iostream>

using namespace std;

class A
{
private:
int a;

public:

void set_a();
void get_a();
void operator !();
};


//Definition of set_a() function
void A :: set_a()
{
	a = 0;
}


//Definition of get_a() function
void A :: get_a()
{
	cout<< a <<"\n";
}


//Definition of overloading unary NOT operator ! function
void A :: operator !()
{
	a = !a;
}



int main()
{
	A ob;
	ob.set_a();

	cout<<"The value of a is : ";
	ob.get_a();

	//Calling operator overloaded function ! to inverse the value
	!ob;

	cout<<"The value of a after calling operator overloading function ! is : ";
	ob.get_a();
}

Output

The value of a is : 0
The value of a after calling operator overloading function ! is : 1

Program Analysis

As you can see in the last program, we have created an operator overloaded member function to successfully overload the meaning of NOT ! operator, in such a way that it could inverse the value of user-defined data type variables and not just built-in data type variables.

In the next article, we are going to explain how to apply operator overloading on binary operators.