653: Mainline

The following revision of the railroad_car class definition shows you how to define a static member variable and how to initialize that member variable. Modified constructors and destructors maintain the static member-variable value, thus keeping track of the total number of railroad cars currently in existence:

class railroad_car {
  public: char *serial_number;
          // Constructors:
          railroad_car ( ) {++counter;}
          railroad_car (char *input_buffer) {
            // Keep track of the number:
            ++counter;
            // Create new array just long enough:
            serial_number = new char[strlen(input_buffer) + 1];
            // Copy string into new array:
            strcpy (serial_number, input_buffer);
          }
          // Destructor:
          virtual ~railroad_car ( ) {
             cout << "Destroying a railroad car; "
                  << --counter << " remain." << endl;
             delete [ ] serial_number;
          }
          // Other:
          virtual char* short_name ( ) {return "rrc";}
          virtual double capacity ( ) {return 0.0;}
  private: static int counter;  
};
int railroad_car::counter = 0;