queue.h

这是一个对数学表达式求值的C++ class

#ifndef QUEUE_CLASS
#define QUEUE_CLASS

// maximum size of a queue list
const int MaxQueueSize = 1000;

template<class T>
class Queue
{
private:
	int front, rear, count;
	T qlist[MaxQueueSize]; // array implementation

public:
	Queue (void);       // initialize integer data members
	void Insert(const T& item);
	T Delete(void);
	void Clear(void);
	T GetFront(void) const;
	int GetLength(void) const;
	bool IsEmpty(void) const;
	bool IsFull(void) const;
};
                                  
// initialize queue front, rear, count
template<class T>
Queue<T>::Queue (void) : front(0), rear(0), count(0)
{}

// insert item into the queue 
template<class T>
void Queue<T>::Insert (const T& item)
{
    // terminate if queue is full
    if (count == MaxQueueSize) {
        cerr << "Queue overflow!" << endl;
        exit(1);
    }
    // increment count, assign item to qlist and update rear
    count++;
    qlist[rear] = item;
    rear = (rear+1) % MaxQueueSize;
}

// delete element from front of queue and return its value
template<class T>
T Queue<T>::Delete(void)
{
	
    // if qlist is empty, terminate the program
    if (count == 0)
    {
        cerr << "Deleting from an empty queue!" << endl;
        exit(1);
    }

    // record value at the front of the queue
    T temp = qlist[front];
    
    // decrement count, advance front and return former front
    count--;
    front = (front+1) % MaxQueueSize;
    return temp;
}

// return value of the first entry 
template<class T>
T Queue<T>::GetFront(void) const
{
    return qlist[front];
}

// return number of queue elements
template<class T>
inline int Queue<T>::GetLength(void) const
{
    return count;
}

// test for an empty queue
template<class T>
inline bool Queue<T>::IsEmpty(void) const
{
    // return the logical value count == 0
    return count == 0;
}

// test for a full queue
template<class T>
inline bool Queue<T>::IsFull(void) const
{
    // return the logical value count == MaxQSize
    return count == MaxQSize;
}

// clear the queue by resetting count, front and rear to 0
template<class T>
void Queue<T>::Clear(void)
{
    count = 0;
    front = 0; 
    rear = 0; 
}

#endif  // QUEUE_CLASS