list.h

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// Fig. 21.4: List.h
// Template List class definition.
#ifndef LIST_H
#define LIST_H

#include <iostream>
using std::cout;

#include <new>
#include "Listnode.h" // ListNode class definition

template< typename NODETYPE >
class List 
{
public:
   List(); // constructor
   ~List(); // destructor
   void insertAtFront( const NODETYPE & );
   void insertAtBack( const NODETYPE & );
   bool removeFromFront( NODETYPE & );
   bool removeFromBack( NODETYPE & );
   bool isEmpty() const;
   void print() const;
private:
   ListNode< NODETYPE > *firstPtr; // pointer to first node
   ListNode< NODETYPE > *lastPtr; // pointer to last node

   // utility function to allocate new node
   ListNode< NODETYPE > *getNewNode( const NODETYPE & );
}; // end class List

// default constructor
template< typename NODETYPE >
List< NODETYPE >::List() 
   : firstPtr( 0 ), lastPtr( 0 ) 
{ 
   // empty body
} // end List constructor

// destructor
template< typename NODETYPE >
List< NODETYPE >::~List()
{
   if ( !isEmpty() ) // List is not empty
   {    
      cout << "Destroying nodes ...\n";

      ListNode< NODETYPE > *currentPtr = firstPtr;
      ListNode< NODETYPE > *tempPtr;

      while ( currentPtr != 0 ) // delete remaining nodes
      {  
         tempPtr = currentPtr;
         cout << tempPtr->data << '\n';
         currentPtr = currentPtr->nextPtr;
         delete tempPtr;
      } // end while
   } // end if

   cout << "All nodes destroyed\n\n";
} // end List destructor

// insert node at front of list
template< typename NODETYPE >
void List< NODETYPE >::insertAtFront( const NODETYPE &value )
{
   ListNode< NODETYPE > *newPtr = getNewNode( value ); // new node

   if ( isEmpty() ) // List is empty
      firstPtr = lastPtr = newPtr; // new list has only one node
   else // List is not empty
   {
      newPtr->nextPtr = firstPtr; // point new node to previous 1st node
      firstPtr = newPtr; // aim firstPtr at new node
   } // end else
} // end function insertAtFront

// insert node at back of list
template< typename NODETYPE >
void List< NODETYPE >::insertAtBack( const NODETYPE &value )
{
   ListNode< NODETYPE > *newPtr = getNewNode( value ); // new node

   if ( isEmpty() ) // List is empty
      firstPtr = lastPtr = newPtr; // new list has only one node
   else // List is not empty
   {
      lastPtr->nextPtr = newPtr; // update previous last node
      lastPtr = newPtr; // new last node
   } // end else
} // end function insertAtBack

// delete node from front of list
template< typename NODETYPE >
bool List< NODETYPE >::removeFromFront( NODETYPE &value )
{
   if ( isEmpty() ) // List is empty
      return false; // delete unsuccessful
   else 
   {
      ListNode< NODETYPE > *tempPtr = firstPtr; // hold tempPtr to delete

      if ( firstPtr == lastPtr )
         firstPtr = lastPtr = 0; // no nodes remain after removal
      else
         firstPtr = firstPtr->nextPtr; // point to previous 2nd node

      value = tempPtr->data; // return data being removed
      delete tempPtr; // reclaim previous front node
      return true; // delete successful
   } // end else
} // end function removeFromFront

// delete node from back of list
template< typename NODETYPE >
bool List< NODETYPE >::removeFromBack( NODETYPE &value )
{
   if ( isEmpty() ) // List is empty
      return false; // delete unsuccessful
   else 
   {
      ListNode< NODETYPE > *tempPtr = lastPtr; // hold tempPtr to delete

      if ( firstPtr == lastPtr ) // List has one element
         firstPtr = lastPtr = 0; // no nodes remain after removal
      else 
      {
         ListNode< NODETYPE > *currentPtr = firstPtr;

         // locate second-to-last element            
         while ( currentPtr->nextPtr != lastPtr )    
            currentPtr = currentPtr->nextPtr; // move to next node

         lastPtr = currentPtr; // remove last node
         currentPtr->nextPtr = 0; // this is now the last node
      } // end else

      value = tempPtr->data; // return value from old last node
      delete tempPtr; // reclaim former last node
      return true; // delete successful
   } // end else
} // end function removeFromBack

// is List empty?
template< typename NODETYPE > 
bool List< NODETYPE >::isEmpty() const 
{ 
   return firstPtr == 0; 
} // end function isEmpty

// return pointer to newly allocated node
template< typename NODETYPE >
ListNode< NODETYPE > *List< NODETYPE >::getNewNode( 
   const NODETYPE &value )
{
   return new ListNode< NODETYPE >( value );
} // end function getNewNode

// display contents of List
template< typename NODETYPE >
void List< NODETYPE >::print() const
{
   if ( isEmpty() ) // List is empty
   {
      cout << "The list is empty\n\n";
      return;
   } // end if

   ListNode< NODETYPE > *currentPtr = firstPtr;

   cout << "The list is: ";

   while ( currentPtr != 0 ) // get element data
   {
      cout << currentPtr->data << ' ';
      currentPtr = currentPtr->nextPtr;
   } // end while

   cout << "\n\n";
} // end function print

#endif

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