Friend function

A friend function is a function that is not a member of a class but has access to the class's private and protected members.

Sample program:

#include <iostream>

class Rectangle

{

   double width;

   public:

   friend void printWidth( Rectangle rectangle );

   void setWidth( double wid );

};

// Member function definition

void Rectangle::setWidth( double wid )

{

    width = wid;

}

// Note: printWidth() is not a member function of any class.

void printWidth( Rectangle rectangle )

{

   /* Because setWidth() is a friend of Rectangle, it can

    directly access any member of this class */

   cout << "Width of Rectangle : " << rectangle.width <<endl;

}

// Main function for the program

int main( )

{

   Rectangle rectangle;

   // set Rectangle width without member function

   rectangle.setWidth(10.0);

  

   // Use friend function to print the width.

   printWidth( rectangle );

   return 0;

}

When the above code is compiled and executed, it produces following result:

Width of Rectangle : 10