Chapter – 5. CONSTRUCTORS & DESTRUCTORS

DELHI 1998

2.a. What is a copy constructor? What do you understand by constructer overloading?

Ans: copy constructor is a constructor of the form classname(classname &). The compiler will use the copy constructor whenever you initialize an instance using values of another instance of same type.
Eg:
Sample S1; //Default constructor used
Sample S2 = S1; //Copy constructor used. Also
//Sample S2(S1);
In the above code, for the second statement, the compiler will copy the instance S1 to S2 member by member. If you have not defined a copy constructor, the compiler automatically, creates it and it is public. A copy constructor takes a reference to an object of the same class an argument.

Constructor Overloading: With same constructor name, having several definitions that are differentiable by the number or types of their arguments(ie Parameterized, non-parameterized and copy constructors) is known as an overloaded constructor and this process is known as constructor overloading.
Constructor overloading implements polymorphism.

An Example using Constructor Overloading:

1.Program to find area of a circle using class, constructor functions and destructor

#include<iostream.h>
#include<conio.h>
class Circle float r,a; //r and a are private
{
public: Circle() //Non parameterized or Default Constructor r=0.0; a=0.0;
{
}
Circle(float rad) //Parameterized Constructor
r = rad;
{ a = 3.1415*r*r;
}
Circle(Circle &obj) //Copy Constructor
r = obj.r;
{
a = obj.a;
}
~Circle()
cout<<"\nThe object is being destroyed....";
{
}
void take()
cout<<"Enter the value of Radius: ";
{
cin>>r;
}
void calculate() a = 3.1415*r*r;
{
}
void display()
cout<<"\nThe Radius of the Circle = "<<r;
{
cout<<"\nThe Area of the Circle = "<<a;
}
};
void main()
clrscr();
{
Circle c1; /*Default Constructor will be called implicitely.
ie c1.r = 0.0 and c1.a = 0.0 */ Circle c2(10.3); //Parameterized Constructor will be called
//implicitely Circle
c3(c2); //Copy Constructor will be called implicitely
c1.take();
c1.calculate();
c1.display();
c2.display();
c3.display();
getch();
}