% cat  list_V.C

/** Linked list V - Using an object and operators to do the dirty work */

   // ~cps330/Examples/list_V.C 

#include <stream.h>
#include <String.h>

class Data_line {
  public:
    String contents;
    Data_line *next;
  }; // End of Data_list class

class Data_list {
  private:
    Data_line *top;            // Will point to the top element

  public:
    Data_list() { top = NULL; cout << "List constructed\n"; }
    ~Data_list() { cout << "List destructing\n" ; }
  
    void operator += (String str);  
    friend ostream & operator << ( ostream & os, const Data_list & listval);
    friend istream & operator >> ( istream & is, const Data_list & listval);
} ;
  
void Data_list::operator += (const String str) 

{

  Data_line *ptr;            // Will point to the new element
  Data_line *prev;           // Previous element (during search)
  Data_line *curr;           // Current element (during search)

  ptr = new Data_line;  // Allocate an object
  cout << "Allocated a new string at " << form("%x",ptr) << "\n";

  ptr->contents = str;    // Copy string into new space

  // Find the position in the list
    
  curr = top;
  prev = NULL;
  while(curr != NULL ) {
    if ( curr->contents > str ) break;
    prev = curr;
    curr = curr->next;
  }

  if ( prev == NULL ) {
     cout << "Adding before the first element\n";
     ptr->next = top;
     top = ptr;
  } else {
     cout << "Adding between " << form("%x",prev) ;
     cout << " and " << form("%x",curr) << "\n";
     ptr->next = curr;
     prev->next = ptr;
  }
} // End of Data_list::operator += 


ostream & operator << ( ostream & os, const Data_list & listval) {
  Data_line *ptr;
  ptr = listval.top; 
  while ( ptr != NULL ) {
    os << ptr->contents << "\n";
    ptr = ptr->next;
  }
  return os;
}

istream & operator >> ( istream & is, Data_list & listval) {
  String input_string;
  cout << "Enter a list element\n";
  readline(is,input_string);
  if ( is.eof() ) return is;
  listval += input_string;
  return is;
}

main() {

  String input_string;       // Used to store string
  Data_list stuff;          // Our ADT

  cout << "Welcome to the beginning of the program\n";

  while(1) { 
    cout << "Enter a string \n";
    cin >> stuff;
    if ( cin.eof() ) break;
  }

  cout << "\n";
  cout << "Here is your list...\n";
  cout << stuff;
  cout << "End of the program\n";

}

% g++  list_V.C
% a.out 
List constructed
Welcome to the beginning of the program
Enter a string 
Enter a list element
my
Allocated a new string at 20056bf8
Adding before the first element
Enter a string 
Enter a list element
favorite  
Allocated a new string at 20056be8
Adding before the first element
Enter a string 
Enter a list element
language
Allocated a new string at 20056c58
Adding between 20056be8 and 20056bf8
Enter a string 
Enter a list element
is
Allocated a new string at 20056c28
Adding between 20056be8 and 20056c58
Enter a string 
Enter a list element
c++
Allocated a new string at 20056c18
Adding before the first element
Enter a string 
Enter a list element
^D
Here is your list...
c++
favorite
is
language
my
End of the program
List destructing
%