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C:/temp/src/j2k/DataType/Queue/LinkedQueue.hpp

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#ifndef __J2K__Linked_Queue_HPP__
#define __J2K__Linked_Queue_HPP__

#include <j2k/Fred/Standard.hpp>
#include <j2k/DataType/Link/SLink.cpp>
    
class LinkedQueue {                      // Linked List Queue class

public:
  inline LinkedQueue()                   // Default Constructor
    : front( NULL ), rear( NULL ) { }

  inline virtual ~LinkedQueue()          // Destructor: return link Elems
  {
    clear();
  }

  void  clear();                         // Remove all Elem's from queue
  void  enqueue( Elem* item );           // Enqueue Elem at rear
  Elem* dequeue();                       // Dequeue Elem from front

  inline Elem* firstValue() const        // Get value of front Elem
  {
    assert( !isEmpty() );
    return front->element;
  }

  inline BOOL isEmpty() const            // Return TRUE if queue is empty
  {
    return front == NULL;
  }

  inline BOOL isFilled() const           // Return TRUE if queue is empty
  {
    return front != NULL;
  }

private:
  SLink* front;                          // Pointer to front queue node
  SLink* rear;                           // Pointer to rear queue node
};

void LinkedQueue::clear()                // Remove all Elem's from the queue
{
  while( front != NULL )                 // Return link nodes to freelist
  {
    rear  = front;
    front = front->next;
    delete rear;
  }
  rear = NULL;
}

// Enqueue Elem at rear of queue
void LinkedQueue::enqueue( Elem* item ) 
{
  if ( rear != NULL )                        // Queue not empty: add to end
  {
    rear = rear->next = new SLink( item, NULL );
  } 
  else 
  {
    front = rear = new SLink( item, NULL );    // Empty queue
  }
}

Elem* LinkedQueue::dequeue()                 // Dequeue Elem from front
{
  assert( !isEmpty() );                      // Must be something to dequeue

  Elem*    temp = front->element;            // Store dequeued value
  SLink*  ltemp = front;                     // Hold onto dequeued link node
          front = front->next;               // Advance front

  delete ltemp;                              // Return link to free store

  if ( front == NULL )                       // Dequeued last element
  {
    rear = NULL;
  }

  return temp;                               // Return element value
}

#endif // End of LinkedQueue.hpp

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