Copy Constructor

In C++, Copy Constructor is a type of constructor that is typically used to create a copy of an already existing object of a class type. It is a constructor that creates an object by initializing it with an object of the same class, that was previously created. 

You can copy the constructor to do the following: 

• To initialize one object from another of the same type. 
• To copy an object to pass it as an argument to a function. 
• To copy an object to return it from a function. 

The compiler can define a copy constructor in a class if the copy constructor was not initially defined. This because the class has pointer variables and has some dynamic memory allocations, and as such, it is must have a copy constructor. 

Below is the general form of a copy constructor:

Syntax:

classname (const classname &obj) {
 // body of constructor
}

From the syntax above, obj is a reference to any object that is used to initialize another object. 

Example:

#include<iostream.h>
#include<conio.h>
class copy
{
int var,fact;
public:
copy(int temp)
 {
  var = temp;
 }
double calculate()
{
fact=1;
for(int i=1;i<=var;i++)
{
fact = fact * i;
}
return fact;                           
}
};

void main()
{
clrscr();
int n;
cout<<"ntEnter the Number : ";
cin>>n;
copy obj(n);
copy cpy=obj;
cout<<"nt"<<n<<" Factorial is:"<<obj.calculate();
cout<<"nt"<<n<<" Factorial is:"<<cpy.calculate();
getch();
}