queue.cpp

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Queue::Queue()
/*   
Post: The Queue is initialized to be empty.
 */
{
   count = 0;
   rear = maxqueue - 1;
   front = 0;
}
 
bool Queue::empty() const
/*   
Post: Return true if the Queue is empty, otherwise
return false.
 */
{
   return count == 0;
}
 
Error_code Queue::append(const Queue_entry &item)
/*   
Post: item is added to the rear of the Queue. If the Queue is full
return an Error_code of overflow and leave the Queue unchanged.
 */
{
   if (count >= maxqueue) return overflow;
   count++;
   rear = ((rear + 1) == maxqueue) ? 0 : (rear + 1);
   entry[rear] = item;
   return success;
}
 
Error_code Queue::serve()
/*   
Post: The front of the Queue is removed. If the Queue 
is empty return an Error_code of underflow.
 */
{
   if (count <= 0) return underflow;
   count--;
   front = ((front + 1) == maxqueue) ? 0 : (front + 1);
   return success;
}
 
Error_code Queue::retrieve(Queue_entry &item) const
/*   
Post: The front of the Queue retrieved to the output
parameter item. If the Queue 
is empty return an Error_code of underflow.
 */
{
   if (count <= 0) return underflow;
   item = entry[front];
   return success;
}