625: Mainline

Fortunately, you know you can have derived constructors call base-class constructors explicitly. The following is a suitable base-class constructor, embedded in the railroad_car class definition:

class railroad_car {
  public: char *serial_number;
          railroad_car ( ) { }
          // New constructor:                                    
          railroad_car (char *input_buffer) {                    
            // Create new array just long enough:                
            serial_number = new char[strlen(input_buffer) + 1];  
            // Copy string into new array:                       
            strcpy (serial_number, input_buffer);                
          }                                                      
          virtual char* short_name ( ) {return "rrc";} 
          virtual double capacity ( ) {return 0.0;} 
}; 

The following defines an engine class constructor so as to make use of the one-parameter railroad_car constructor:

class engine : public railroad_car {
  public: engine ( ) { }
          // New constructor:
          engine (char *input_buffer) : railroad_car (input_buffer)  
            { }                                                      
          virtual char* short_name ( ) {return "eng";} 
};