785: Mainline

In the following program, the expression railroad_car, provided as a template argument in the expression iterator<railroad_car> train_iterator (train), causes the iterator class to be instantiated so as to deal with railroad cars. The expression train provides the new iterator with access to a particular list of railroad cars.

#include   
#include   
const double pi = 3.14159; 
// Container, railroad-car, and list definitions go here 
template  
class iterator { 
  public: 
    iterator (header& header) { 
      first_link_pointer = header.first_link_pointer; 
      current_link_pointer = first_link_pointer; 
    } 
    iterator_parameter* access ( ) { 
      return current_link_pointer -> element_pointer; 
    } 
    void advance ( ) { 
      current_link_pointer = current_link_pointer -> next_link_pointer; 
    } 
    int endp ( ) { 
      return ! current_link_pointer; 
    } 
    void reset ( ) { 
      current_link_pointer = first_link_pointer; 
    } 
  private: link* current_link_pointer; 
           link* first_link_pointer; 
}; 
// Define list header: 
header train; 
char input_buffer[100]; 
enum {eng_code = 'E', box_code = 'B', tnk_code = 'T', cab_code = 'C'}; 
char extract_car_code (char *input_buffer) {return input_buffer[4];} 
main ( ) { 
  // Collect train elements as usual 
  // Define and initialize iterator class object: 
  iterator train_iterator (train); 
  // Iterate: 
  train_iterator.reset ( ); 
  for (; !train_iterator.endp ( ) ; train_iterator.advance ( ))  
    // Display number, short name, and capacity and terminate the line:  
    cout << train_iterator.access ( ) -> serial_number << "     " 
         << train_iterator.access ( ) -> short_name ( ) << "     " 
         << train_iterator.access ( ) -> capacity ( ) << endl; 
} 
--- Data ---
TPW-E-783 
PPU-B-422 
NYC-B-988 
NYC-T-988 
TPW-C-271 
--- Result --- 
TPW-C-271     cab     0 
NYC-T-988     tnk     1539.38 
NYC-B-988     box     3990 
PPU-B-422     box     3990 
TPW-E-783     eng     0 

Note that you can remove the access, advance, endp, and reset member functions from the header class, forcing all list traversal to be done with a iterator object.