manas111

 Profile Answers by manas111 

• Jan 13th, 2011

 

Constructor having reference type parameter;
It is used to declare & initialise an object from another object.

amitmanish

 Profile Answers by amitmanish 

• Mar 4th, 2011

 

Copy contructor is parameterised constructor with a argument which is a reference to an object of the class.

Why we need a reference?
the answer is that if we don't use a reference and instead use an object to pass an argument it will again need a call to the copy constructor to create a copy which in turn again does the same, this leads to an infinite chain of such calls.

Assignment operator as well as copy constructor do a shallow copy, i.e for an example as below instead of putting the address of the variable o4.a of into o4.ptr it copies the address stored in o1.ptr into o4.ptr. But this behaviour can be changed by writting a custom module for both.

The following code illustrates where copy constructor is invoked and where an assignment operator is invoked.

#include<iostream.h>
class A
{
    public:

    int a;
    int *ptr;

    A(){a = 10; ptr = &a;}
    A(A &b) // if we use A(A b) here this invokes copy constructor recursively
    {
        a = b.a;
        ptr = &a; //changing the default behavior of shallow copying which woud be
                       // an equivalent of ptr = b.ptr
    }
};

void main()
{
    A o1;
    A o2(o1);  //copy contructor
    A o3  =  o1; //copy contructor
    A o4;
    o4 = o1; //assignment operator

    cout<<o1.a<<'n';
    cout<<o1.ptr<<'n';

    cout<<o2.a<<'n';
    cout<<o2.ptr<<'n';

    cout<<o1.a<<'n';
    cout<<o1.ptr<<'n';

}