c07p346.txt

Data Abstraction & Problem Solving with C++源码

// ********************************************************
// Header file QueueP.h for the ADT queue.
// Pointer-based implementation.
// ********************************************************
#include "QueueException.h"
typedef desired-type-of-queue-item QueueItemType;

class Queue
{
public:
// constructors and destructor:
   Queue();                     // default constructor
   Queue(const Queue& Q);       // copy constructor
   ~Queue();                    // destructor

// Queue operations:
   bool isEmpty() const;
   // Determines whether the queue is empty.
   // Precondition: None.
   // Postcondition: Returns true if the queue is empty;
   // otherwise returns false.

   void enqueue(QueueItemType newItem);
   // Inserts an item at the back of a queue.
   // Precondition: newItem is the item to be inserted.
   // Postcondition: If the insertion is successful, newItem
   // is at the back of the queue.

   void dequeue() throw(QueueException);
   // Dequeues the front of a queue.
   // Precondition: None.
   // Postcondition: If the queue is not empty, the item
   // that was added to the queue earliest is deleted.
   // Exception: Throws QueueException if the queue is
   // empty.

   void dequeue(QueueItemType& queueFront)
	   throw(QueueException);
   // Retrieves and deletes the front of a queue.
   // Precondition: None.
   // Postcondition: If the queue is not empty, queueFront
   // contains the item that was added to the queue
   // earliest, and the item is deleted.
   // Exception: Throws QueueException if the queue is
   // empty.

   void getFront(QueueItemType& queueFront) const
          throw(QueueException);
   // Retrieves the item at the front of a queue.
   // Precondition: None.
   // Postcondition: If the queue is not empty, queueFront
   // contains the item that was added to the queue
   // earliest.
   // Exception: Throws QueueException if the queue is
   // empty.

private:
   // The queue is implemented as a linked list
   // with one external pointer to the front of the queue
   // and a second external pointer to the back of the
   // queue.
   struct QueueNode
   {  QueueItemType  item;
      QueueNode     *next;
   }; // end struct
   QueueNode *backPtr;
   QueueNode *frontPtr;
};  // end class
// End of header file.