c07p354.txt

Data Abstraction & Problem Solving with C++源码

// ********************************************************
// Implementation file QueueA.cpp for the ADT queue.
// Circular array-based implementation.
// The array has indexes to the front and back of the
// queue. A counter tracks the number of items currently
// in the queue.
// ********************************************************
#include "QueueA.h"  // header file

Queue::Queue():front(0), back(MAX_QUEUE-1), count(0)
{
}  // end default constructor

bool Queue::isEmpty() const
{
   return count == 0);
}  // end isEmpty

void Queue::enqueue(QueueItemType newItem) throw(QueueException)
{
   if (count == MAX_QUEUE)
      throw QueueException("QueueException: queue full on enqueue");
   else
   {  // queue is not full; insert item
      back = (back+1) % MAX_QUEUE;
      items[back] = newItem;
      ++count;
   }  // end if
}  // end enqueue

void Queue::dequeue() throw(QueueException)
{
   if (isEmpty())
      throw QueueException("QueueException: empty queue, cannot dequeue");
   else
   {  // queue is not empty; remove front
      front = (front+1) % MAX_QUEUE;
      --count;
   }  // end if
}  // end dequeue

void Queue::dequeue(QueueItemType& queueFront) throw(QueueException)
{
   if (isEmpty())
      throw QueueException("QueueException: empty queue, cannot dequeue");
   else
   {  // queue is not empty; retrieve and remove front
      queueFront = items[front];
      front = (front+1) % MAX_QUEUE;
      --count;
   }  // end if
}  // end dequeue

void Queue::getFront(QueueItemType& queueFront) const
                     throw(QueueException)
{
   if (isEmpty())
      throw QueueException("QueueException: empty queue, cannot getFront");
   else
      // queue is not empty; retrieve front
      queueFront = items[front];
}  // end getFront
// End of implementation file.