Constructor and Destructors in C++

1. Constructor & Destructors in C++
• Constructor Definition
• Types of Constructor
• Default Constructor
• Parameterized Constructor
• Copy Constructor
By
Prof. Sandeep Vishwakarma

8. Types of Constructors
• Default Constructor
• Parameterized Constructor
• Copy Constructor

10. #include <iostream.h>
#include <conio.h>
class Employee
{
public:
Employee()
{
cout<<"Default Constructor Invoked"<<endl;
}
};
int main(void)
{
Employee e1; //creating an object of Employee
Employee e2;
getch();
}

17. #include<iostream.h>
#include<conio.h>
class Employee
{
public:
int id;
string name;
float salary;
Employee(int i, string n, float s)
{
id = i;
name = n;
salary = s;
}
Parameterized Constructor Example

18. void display()
{
cout<<id<<" "<<name<<" "<<salary<<endl;
} };
int main()
{
Employee e1 =Employee(101, "Sandeep",12000);
Employee e2=Employee(102, "Amit", 15000);
e1.display();
e2.display();
getch();
}

20. When Copy Constructor is called
• When we initialize the object with another
existing object of the same class type. For
example, Student s1 = s2, where Student is
the class.
• When the object of the same class type is
passed by value as an argument.
• When the function returns the object of the
same class type by value.

21. #include<iostream.h> Copy Constructor Example
#include<conio.h>
class A
{
public: int x;
A(int a) // parameterized constructor.
{
x=a;
}
A(A &i) // copy constructor
{
x = i.x;
} };
int main()
{
A a1(20); // Calling the parameterized constructor.
A a2(a1); // Calling the copy constructor.
cout<<a2.x;
getch(); }

24. Thank You

25. Constructor in C++
• Destructor in C++
• Constructor Overloading
• Constructor Overloading Example
• This Keyword
• Hands on Example
By
Prof. Sandeep Vishwakarma

27. Rules for Destructors
• Destructor is a type of special member function of a
class.
• It is used to destroy the memory allocated by the
constructor.
• It has the same name as the class prefixed with a tilde
(~) sign.
• Destructor does not take any arguments and cannot
return or accept any value.
• It is called automatically by the compiler when the
object goes out of scope.
• Compiler calls the destructor implicitly when the
program execution is exited.

33. Example - 1 Constructor Overloading
class Student
{
public:
int rollno;
string name;
Student(int x) // first constructor
{
rollno = x;
name = "None";
}

34. Student(int x, string str) // second constructor
{
rollno = x;
name = str;
}};
int main()
{
Student A(10);
Student B(11, "John");
getch();
}

35. Example - 2 Constructor Overloading
#include <iostream.h>
#include <conio.h>
class ABC
{
private:
int x,y;
public:
ABC () //constructor 1 with no arguments
{
x = y = 0;
}
ABC(int a) //constructor 2 with one argument
{
x = y = a;
}

36. ABC(int a, int b) //constructor 3 with two argument
{
x = a;
y = b;
}
void display()
{
cout << "x = " << x << " and " << "y = " << y << endl;
} };
int main()
{
ABC cc1; //constructor 1
ABC cc2(10); //constructor 2
ABC cc3(10,20); //constructor 3
cc1.display();
cc2.display();
cc3.display();
getch(); }

37. this Keyword
this is a keyword that refers to the current
instance of the class. There can be 3 main
usage of this keyword in C++.
• It can be used to pass current object as a
parameter to another method.
• It can be used to refer current class
instance variable.
• It can be used to declare indexers.

38. Example: this Keyword
#include <iostream.h>
#include <conio.h>
class Employee
{
public:
int id; //data member (also instance variable)
string name; //data member(also instance variable)
float salary;
Employee(int id, string name, float salary)
{
this->id = id;
this->name = name;
this->salary = salary;
}

39. void display()
{
cout<<id<<" "<<name<<" "<<salary<<endl;
} };
int main(void)
{
Employee e1 =Employee(101, “Amit", 12000);
Employee e2=Employee(102, "Nakul", 15000);
e1.display();
e2.display();
getch();
}

40. Thank You