Friend Function in C++

Friend Function in C++

A friend function in C++  is defined as outside that class and it has the right to access all private members and protected members of the class.

A friend function define as  a function of the class defined outside the class scope and if a function is defined as a friend function then, the private and protected data of class.

Friend function is declared by using friend keyword.

Syntax of friend function

class className {
    ... .. ...
    friend returnType functionName(arguments);
    ... .. ...
}

Program of friend function

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

Output

Length of box: 10  

Read more, Inheritance types in C++