Explain use of friend function in C++ with examples?

In this chapter of C++ interview questions, we will learn:

• what is friend function in c++ with example?
• use of friend function in c++

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What is friend function in C++?

A friend function of a class is defined outside class but it can access all private and protected members of the class.

 

A friend function in c++ can be of two types:

1. global function,
2. method of another class.

It is not a member function and can't get 'this' pointer.

 

Need or use of friend function in C++

If a function required to built with have access of private members of a class, this type of scenario friend function in c++ is required.

 

Mostly this type of situation arises in operator overloading.

Example of friend function in C++

Lets see an example that use friend function in C++:

#include<iostream>
using namespace std;

class Square
{
  double side;

  public:
   friend void plength(Square S); // friend function
   void slength(double sd); //slength() member function of Square class
};

void Square::slength(double sd)
{
  side=sd;
}
void plength(Square S) //plength() is friend of Square
{
  cout<<"Length of Square"<<" "<<S.side;
  cout<<endl;
}

int main()
{
  Square S;
  S.slength(13.0);
  plength(S); //friend function for print length
  return 0;
}

OUTPUT

Length of Square 13.0