Hi all

when we try to copy one object into another using copy constructer we need to maintain the original copy of original object (which we are copying) so while passing object we make it constant and we pass it as a by reference.

Thanks & Regards

Ms.Supriya Ahire.

It is not Const. pointer in copy constructor but const Reference of object of same class type which we do pass in copy constructor.... and everyone has given pretty good answers for two questions

1) what is importance of const. reference object of same class type in copy const...

2) Why do we use reference of class instead of simple pass by value.

Again one query why dont we use pass by pointer in copy constructor so see following scenario

class ABC
{
public:
ABC(){} /*Simple Constructor*/
ABC(ABC * b) { }/*Copy Constructor*/
};

int main(int argc char* argv[]){
ABC * d1 NULL;
ABC d2 d1; /*Calling Copy constructor*/
return 0;
}

See above example if we take pointer type object in copy constructor

two flaws are here 1) We can assign NULL value to simple object of that class

2) see this line ABC d2 d1;

here d2 is ABC type while d1 is ABC* type means as per rule we are violating basic rules by allowing to assign simple type with pointer type.

If there is any pointer type member variable in side ABC class means DEEP Copy scenario like int * m_iVal; then it will crash out during calling copy constructor by passing NULL object... so stop such mistake at design time we do use const reference object of same class type in copy constructor as a parameter.Hoping this will clear you.

Copy constructor is useful when an object is initialized with another existing object or an object is passed by value to a function or an object is returned by value from a function. Shallow copy is nothing but copying members of a class by value so when an object is copied into another object all members will copied by value and if dynamic memory allocation is there the pointer will be copied but not the memory to which the pointer is pointing too. So the pointers in old and new pointing to same memory allocation. If the old objects is deleted memory to pointer is also deleted. In this case when the new object trying to access the same memory crash will happen. This can be avoided with copy constructor explicit declaration. in the below code I created memory to the char pointer name again in copy constrctor and copied the value. I hope this gives you better idea.. Thanks

#include<iostream.h>
#include<string.h>

class A

{public:

char *name;

A(){

name new char[20];

strcpy(name ramachandra );

}

A(const A &a)

{

name new char[20];

strcpy(name a.name);

}

};

void main()

{

A a;

cout<<a.name n;

A b a;

cout<<b.name n;

}