constructors and destructors

constructors

Constructors are special class members which are called by the compiler every time an object of that class is instantiated. Constructors have the same name as the class and may be defined inside or outside the class definition.
There are 3 types of constructors:

§  Default constructors

§  Parametrized constructors

§  Copy constructors

// C++ program to demonstrate constructors #include <bits/stdc++.h> using namespace std; class Geeks {     public:     int id;           //Default Constructor     Geeks()     {         cout << "Default Constructor called" << endl;         id=-1;     }           //Parametrized Constructor     Geeks(int x)     {         cout << "Parametrized Constructor called" << endl;         id=x;     } }; int main() {           // obj1 will call Default Constructor     Geeks obj1;     cout << "Geek id is: " <<obj1.id << endl;           // obj1 will call Parametrized Constructor     Geeks obj2(21);     cout << "Geek id is: " <<obj2.id << endl;     return 0; }

Run on IDE

Output:

Default Constructor called

Geek id is: -1

Parametrized Constructor called

Geek id is: 21

A Copy Constructor creates a new object, which is exact copy of the existing copy. The compiler provides a default Copy Constructor to all the classes.
Syntax:

class-name (class-name &){}

Destructors

Destructor is another special member function that is called by the compiler when the scope of the object ends.

// C++ program to explain destructors #include <bits/stdc++.h> using namespace std; class Geeks {     public:     int id;           //Definition for Destructor     ~Geeks()     {         cout << "Destructor called for id: " << id <<endl;     } }; int main()   {           Geeks obj1;     obj1.id=7;     int i = 0;     while ( i < 5 )     {         Geeks obj2;         obj2.id=i;         i++;               } // Scope for obj2 ends here     scope     return 0;   } // Scope for obj1 ends here

Run on IDE

Output:

Destructor called for id: 0

Destructor called for id: 1

Destructor called for id: 2

Destructor called for id: 3

Destructor called for id: 4

Destructor called for id: 7