C++函数调用运算符()重载

#include <iostream>
using namespace std;

class Distance {
   private:
      int feet;             // 0 to infinite
      int inches;           // 0 to 12

   public:
      // required constructors
      Distance() {
         feet = 0;
         inches = 0;
      }
      Distance(int f, int i) {
         feet = f;
         inches = i;
      }

      // overload function call
      Distance operator()(int a, int b, int c) {
         Distance D;

         // just put random calculation
         D.feet = a + c + 10;
         D.inches = b + c + 100 ;
         return D;
      }

      // method to display distance
      void displayDistance() {
         cout << F:  << feet <<  I: << inches << endl;
      }   
};

int main() {
   Distance D1(11, 10), D2;

   cout << First Distance : ; 
   D1.displayDistance();

   D2 = D1(10, 10, 10); // invoke operator()
   cout << Second Distance :; 
   D2.displayDistance();

   return 0;
}