Copy constructor

What is copy constructor? Discuss two situations when a copy constructor is automatically invoked giving appropriate examples.

Copy constructor is

• a constructor function (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. (Find its example in BLUE colour)

For ex:
class A //Without copy constructor

{ private:
int x;
public:
A() {A = 10;}
~A() { }
};

---

class B //************** With copy constructor ************
{
private:
int month;
public:
B( int y) //********* Parameterized constructor ***********
{
month = y;
}
~B( )
{
cout << "destructor function invoked"; }

B( B &b) //*************** Copy constructor *************
{
month = b.month;
}

};

---

class B //With copy constructor
{
private:
char *name;
public:
B()
{
name = new char[20];
}
~B()
{
delete name[];
}
//Copy constructor
B(B &b)
{
name = new char[20];
strcpy(name, b.name);
}
};

---

Example : When an object is created from another object of the same type

class A
{ int a;
public:
A(int x )
{ cout <<"Constructor invoked ..."; a=x; } }Obj1(23); A Obj2=Obj1; }

---

Example :
1. When an object is passed by value as a parameter to a function
2.When an object is returned from a function

class time
{ int hr;
int min;
public:
time ( ) // ******** constructor function ********
{ hr = min = 0;}
void gettime(int x,int y) {hr=x;min=y;}
void showtime( ) { cout <<" : " <<<"\n";} };

time addtime( time T1, time T2)
{ time T3;
T3.hr = T1.hr + T2.hr;
T3.min = T1.min + T2.min;
if (T3.min >= 60)
{ T3.min =T3.min - 60;
T3.hr = T3.hr+1;
}
return T3;
}

void main( )
{ time X1 (5,45); // Parameterized constructor Invoked
time X2 (7,40); // Parameterized constructor Invoked
time X3=addtime(X1,X2); // Copy Constructor invoked
X3.showtime( ); // This will show the time as 13 : 25
}

---