C++ Constructor and Destructor

C++ Constructor

In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure.

There can be two types of constructors in C++.

• Default constructor
• Parameterized constructor

---

C++ Default Constructor

A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.

Let's see the simple example of C++ default Constructor.

1. #include <iostream>  
2. using namespace std;  
3. class Employee  
4.  {  
5.    public:  
6.         Employee()    
7.         {    
8.             cout<<"Default Constructor Invoked"<<endl;    
9.         }    
10. };  
11. int main(void)   
12. {  
13.     Employee e1; //creating an object of Employee   
14.     Employee e2;   
15.     return 0;  
16. }  

Output:

Default Constructor Invoked 
Default Constructor Invoked

C++ Parameterized Constructor

A constructor which has parameters is called parameterized constructor. It is used to provide different values to distinct objects.

Let's see the simple example of C++ Parameterized Constructor.

#include <iostream>
using namespace std;
class Employee {
   public:
       int id;//data member (also instance variable)    
       string name;//data member(also instance variable)
       float salary;
       Employee(int i, string n, float s)  
        {  
            id = i;  
            name = n;  
            salary = s;
        }  
       void display()  
        {  
            cout<<id<<"  "<<name<<"  "<<salary<<endl;  
        }  
};
int main(void) {
    Employee e1 =Employee(101, "Sonoo", 890000); //creating an object of Employee 
    Employee e2=Employee(102, "Nakul", 59000); 
    e1.display();  
    e2.display();  
    return 0;
}

Output:

101  Sonoo  890000
102  Nakul  59000

C++ Destructor

A destructor works opposite to constructor; it destructs the objects of classes. It can be defined only once in a class. Like constructors, it is invoked automatically.

A destructor is defined like constructor. It must have same name as class. But it is prefixed with a tilde sign (~).

Note: C++ destructor cannot have parameters. Moreover, modifiers can't be applied on destructors.

C++ Constructor and Destructor Example

Let's see an example of constructor and destructor in C++ which is called automatically.

1. #include <iostream>  
2. using namespace std;  
3. class Employee  
4.  {  
5.    public:  
6.         Employee()    
7.         {    
8.             cout<<"Constructor Invoked"<<endl;    
9.         }    
10.         ~Employee()    
11.         {    
12.             cout<<"Destructor Invoked"<<endl;    
13.         }  
14. };  
15. int main(void)   
16. {  
17.     Employee e1; //creating an object of Employee   
18.     Employee e2; //creating an object of Employee  
19.     return 0;  
20. }  

Output:

Constructor Invoked
Constructor Invoked
Destructor Invoked
Destructor Invoked

Anurag Rana Educator CSE/IT