C++友元函数

#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;
}