Operator Overloading in C++

1. When an operator is overloaded with multiple jobs, it is known as operator overloading.

2. Operator overloading is a way to implement compile time polymorphism.

3. Any symbol can be used as function name if

(a.) if it is a valid operator in C language.

(b.) if it is preceded by operator keyword.

4. We cannot overload sizeof operator and ternary (?:) operator.

For Example:-

#include<iostream>
using namespace std;

class Complex
{
private:
  int real, imaginary;
  
public:
  void setData(int num1, int num2)
  {
    real = num1;
    imaginary = num2;
  }
  
  void showData()
  {
    cout << real << " " << imaginary;
  }
  
  Complex operator+(Complex C)      //operator overloading of + symbol.
  {
    Complex temp;
    
    temp.real = real+C.real;
    temp.imaginary = imaginary+C.imaginary;
    
    return temp;
  }
};

int main()
{
  Complex C1,C2,C3;
  
  C1.setData(3,4);
  C2.setData(5,6);
  
  C3 = C1+C2;       //calling operator overloading.
  C3.showData();
}

Output:

8 10

Overloading of Unary Operator

Operator which takes only one operand to perform operation is called unary operator. To know more about different types of operator, you should check this >> Operators

Unary operator can be overloaded as follows.

For Example:-

#include<iostream>
using namespace std;

class Complex
{
private:
  int real, imaginary;

public:
  void setData(int num1, int num2)
  {
    real = num1;
    imaginary = num2;
  }
  
  void showData()
  {
    cout<< real << " " << imaginary;
  }
  
  Complex operator-()      //operator overloading of unary operator -.
  {
    Complex temp;
    
    temp.real = -real;
    temp.imaginary = -imaginary;
    
    return temp;
  }
};

int main()
{
  Complex C1,C2;
  C1.setData(9,2);
  
  C2 = -C1;             //C2=c1.operator-()  calling unary operator overloading.
  C2.showData();
}

Output:

-9 -2

Pre and Post increment Operator Overloading

The symbol of prefix (++i) and postfix (i++) operator is same so we need to use a dummy int as parameter in postfix version to distinguish between the two functions definition.

For Example:-

#include<iostream>
using namespace std;

class Integer
{
private:
  int num;
  
public:
  void setData(int a)
  {
    num = a;
  }
  
  void showData()
  {
    cout << "\n integer is: "<< num;
  }

  Integer operator++()        //preincrement operator overloading.
  {
    Integer i;
    i.num = ++num;
    return i;
  }
  
  Integer operator++(int)     //postincrement operator overloading.
  {
    Integer i;
    i.num = num++;
    return i;
  }
};

int main()
{
  Integer i1, i2;
  
  i1.setData(55);
  i1.showData();
  
  i2 = i1++;        //i2=i1.operator++()
  i2.showData();
  
  i2 = ++i1;
  i2.showData();
}

Output:

 integer is: 55
 integer is: 55
 integer is: 57

For more information: Operator overloading as a friend function, overloading of unary operator as a friend function, insertion and extraction operator overloading.

Read Here >> More on Operator Overloading

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Operator Overloading in C++