12. Overloaded operator <<

• C++ allows operator syntax for user-defined types:

  
      #include <iostream>
  
      int serial_julian_date( int Month, int Day, int Year );
      int serial_2_month( int nDate );
      int serial_2_day( int nDate );
      int serial_2_year( int nDate );
  
      class Date {
          // member variables
          int serial_date;
      public:
          // member functions
          void set_date( int month, int day, int year ) {}
          int get_month() { return 2; }
          int get_day() { return 8; }
          int get_year() { return 1999; }
      };
  
      void operator<<( std::ostream&, Date dt )
      {
          std::cout << dt.get_month();
          std::cout << '/';
          std::cout << dt.get_day();
          std::cout << '/';
          std::cout << dt.get_year();
      }
  
      int main()
      {
          Date birthday; // instantiate object of type "Date"
          birthday.set_date( 2, 8, 1999 ); // member function calls
          std::cout << birthday;
          return 0;
      }