Course Introduction
Friend function
A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class.
Even though the prototypes for friend functions appear in the class definition, friends are not member functions..
Source Code:Friend Function
/* C++ Program - Friend Function */
#include <iostream>
using namespace std;
class Box {
double width;
public:
friend void printWidth( Box box );
void setWidth( double wid );
};
// Member function definition
void Box::setWidth( double wid ) {
width = wid;
}
// Note: printWidth() is not a member function of any class.
void printWidth( Box box ) {
/* Because printWidth() is a friend of Box, it can
directly access any member of this class */
cout << "Width of box : " << box.width <<endl;
}
// Main function for the program
int main() {
Box box;
// set box width without member function
box.setWidth(10.0);
// Use friend function to print the wdith.
printWidth( box );
return 0;
}
When the above code is compiled and executed, it produces the following result −
Width of box : 10
