Copy constructor

Copy constructor is

* a constructor function with the same name as the class
* used to make deep copy of objects.

There are 3 important places where a copy constructor is called.

1. When an object is created from another object of the same type
2. When an object is passed by value as a parameter to a function
3. When an object is returned from a function

If a copy constructor is not defined in a class, the compiler itself defines one. This will ensure a shallow copy. If the class does not have pointer variables with dynamically allocated memory, then one need not worry about defining a copy constructor. It can be left to the compiler's discretion.

But if the class has pointer variables and has some dynamic memory allocations, then it is a must to have a copy constructor.

For ex:
class A //Without copy constructor
{
private:
int x;
public:
A() {A = 10;}
~A() {}
}
class B //With copy constructor
{
private:
char *name;
public:
B()
{
name = new char[20];
}
~B()
{
delete name[];
}
//Copy constructor
B(const B &b)
{
name = new char[20];
strcpy(name, b.name);
}
};