special functions in C++ - Sharp Tutorial

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Friend Function in C++

Friend function is used to access the private data of a class .For this we need to declare the function as friend function

Program on friend function

 #include <iostream>  
using namespace std;  
class Box  
{  
    private:  
        int length;  
    public:  
        Box(): length(0) { }  
        friend int printLength(Box); //friend function  
};  
int printLength(Box b)  
{  
    b.length += 10;  
    return b.length;  
}  
int main()  
{  
    Box b;  
    cout<<"Length of box: "<< printLength(b)<<endl;  
    return 0;  
}

Output of the above program is as follows

Virtual function in c++

 #include <iostream>  
using namespace std;  
class A  
{  
 public:  
 virtual void display()  
 {  
  cout << "Base class is invoked"<<endl;  
 }  
};  
class B:public A  
{  
 public:  
 void display()  
 {  
  cout << "Derived Class is invoked"<<endl;  
 }  
};  
int main()  
{  
 A* a;    //pointer of base class  
 B b;     //object of derived class  
 a = &b;  
 a->display();   //Late Binding occurs  
}

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