CONSTRUCTOR IN C ++

Constructor:

• In c ++ Constructor is a special member function of class.
• Constructor is used for initializing the object of a class.

Rules for writing constructor:-

1. Constructor will have same name as the class name.
2. Constructor will get invoked automatically when a object of a class is created.
3. Constructor will not return any value./Constructor will not have return type.
4. Constructor should always declared in public area of the class.
5. Main job of the constructor is to initialize the object of the class.

NOTE: Points to remember

(1)We can not create a virtual constructor.

(2)Even if we don’t define a constructor explicitly compiler will provide a default constructor implicitly.

(3)We can overload constructor.

• Types of constructor:-

1. Parameterized constructor
2. Default constructor
3. Copy constructor

1.Parametrrized constructor-

The constructor in which it is possible to pass the arguments to a constructor which helps to initialize a object is called a parameterized constructor.

syntax- classname(parameters)

Example-

#include<iostream>

using namespace std;

class Box
{
int x, y;
public:
Box(int b1,int b2)
{
x=b1;
y=b2;
}
int getX()
{
return x;
}
int getY()
{
return y;
}
};
int main()
{
Box myobj(30,25);
cout<< “ X: “<<myobj.getX()<<endl;
cout<<”Y: “ <<myobj.getY();
return 0;
}

Output:

X=30

Y=25

2.Deafault constructor-

A constructor which does not take ant arguments is knows as default constructor.

syntax- calssname()

Example-

#include <iostream>

using namespace std;
class box
{
int a ,b;

public:
box()
{
a=35;
b=24;

}
int geta()
{
return a;
}
int getb()
{
return b;
}

};

int main()
{
box b1;
cout<<”a: “<<b1.geta()<<endl;
cout<<”b: “<<b1.getb();

return 0;
}

Output-

a=35

b=24

3.Copy constructor-

A constructor which is used to copy the data of one constructor to another is known as copy constructor.

syntax-calssname (const classname & old_obj)

Example-

#include <iostream>

using namespace std;
class box
{
int x,y;

public:
box(int m,int n)// main constructor call
{
x=m;
y=n;
}

box(const box &b1)//copy constructor
{
x=b1.x;
y=b1.y;

}
int getx()
{
return x;

}
int gety()
{
return y;

}
};

int main()
{
box b1(35,74);
box b2=b1;
cout<<”value of x in b1: “<<b1.getx()<<endl;
cout<<”value of y in b1: “<<b1.gety()<<endl;
cout<<”value of x in b2: “<<b2.getx()<<endl;
cout<<”value of y in b2: “<<b2.gety()<<endl;

return 0;
}

Output-

value of x in b1: 35
value of y in b1: 74
value of x in b2: 35
value of y in b2: 74