Explain friend member function with example.

(This question has been asked in GU Uni Dec 2018 for 7 Mark)

Friend Functions

Non-member function which is declared as a friend of particular class can have access to private data members of that class, in which it is declared as friend.

To make outside function (non-member) function friend of particular class we have to use ‘friend’ ‘keyword.

Simply, use the ‘friend’ keyword before function prototype. Consider below example,

#include <iostream>
using namespace std; 

class Box
{
	int width; //private
	public:
	void setData(int w)
	{
		width=w;
	}
	void getData()
	{
		cout<<"width:" <<width;
	}
	friend void display(Box );
};

void display(Box obj)       //non member function
{
	cout<< "Width from display function:"<< obj.width<<endl;

}

int main()
{

	Box mybox;
	
	cout<<"Box Program"<<endl;

	mybox.setData(20); //erro
	mybox.getData();

	display(mybox);
	return 0; 
}

OUTPUT

Box Program
width:20Width from display function:20

https://github.com/amitntrivedi/ObjectOrientedConceptsandProgramming/blob/master/Friend%20Function/FriendFunctionAndBoxClass.CPP