Copy Constructor
The copy constructor is used to copy the content of one object to another object. A copy constructor always takes a reference object as an argument. A copy constructor can be defined in two ways:
i) Inside the class definition
ii) Outside the class definition
i) Inside the class definition
The general form of defining a copy constructor holds the following syntax.
class classname
{
private:
//Data members
public:
classname(classname &object_name)
{
//Copy Constructor Statements
}
};
ii) Outside the class definition
The general form of defining a copy constructor outside the class holds the following syntax.
class classname
{
private:
//Data members
public:
classname(classname &object_name); // Copy Constructor prototype
};
classname::classname(classname &object_name) < --------------------- Outside the class
{
// Copy Constructor Statements
}
Remember
When the copy constructor is defined outside the class, its prototype must be declared in the public category of the class.
Invoking a copy constructor
We must pass the initial values as arguments to copy constructor after initializing the source object
Method1
class_name destination_object=source_object;
Example
demo d1(4500);
demo d2=d1;
Method2
class_name destination_object(source_object);
Example
demo d1(4500);
demo d2(d1);
The programmer can use either of the methods.
Program 4.3
Write a program to provide same salary to three employees using copy constructor.
#include<iostream.h>
#include<constream.h>
class employee
{
private:
int salary;
public:
employee(int);
employee(employee&);
void display();
};
employee::employee(int val)
{
salary=val;
}
employee::employee(employee &e)
{
salary=e.salary;
}
void employee::display()
{
cout<<salary<<endl;
}
main()
{
clrscr();
employee e1(4500);
employee e2(e1);
employee e3=e2;
cout<<"Salary of employee1 :";e1.display();
cout<<"Salary of employee2 :";e2.display();
cout<<"Salary of employee3 :";e3.display();
return(0);
}
Output
Salary of employee1 :4500
Salary of employee2 :4500
Salary of employee3 :4500
Explanation
In the above program, the source object e1 is initialized first, then its content is assigned to destination object e2 and e3 as declared in the main( ) function.
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