用循环链表实现队列

#include<iostream>
#include<ctime>//...
#include<stdlib.h>//随机数要的
using namespace std;
template<typename T>
class listNode//只是一个节点
{
public:
  T NodeData;
  listNode *next;
  listNode(T data, listNode * ne){ NodeData = data; next = ne; }
  listNode(){ NodeData = NULL; next = NULL; }
};
template<typename T>
class Queue
{
public:
  Queue();
  Queue(const  Queue<T> & or);
  void enqueue(const T & item);//
  void dequeue();//
  const T & front() const;
  bool empty() const;//
  void display() const;
  Queue & operator =(const Queue<T> &or);
  ~Queue();
private:
  listNode<T>* myBack;
};
template<typename T>
Queue<T>::Queue(){ myBack = new listNode<T>(); myBack->next = myBack; }//这个myback已经成了最简单的循环列表，指向它自己，这个myback都是留着不放东西的，也将是是否为空的判断依据！
template<typename T>
Queue<T>::Queue(const  Queue<T>& or)
{ 
  myBack = new listNode<T>();
  myBack->next = myBack;
  listNode<T> *pr = or.myBack->next,*pt=myBack->next;
  myBack->NodeData = or.myBack->NodeData;
  myBack->next = myBack;
  while (pr !=or.myBack)
  {
    pt = new listNode<T>(NULL, myBack->next);
    myBack->NodeData = pr->NodeData;
    myBack->next = pt;
    myBack = pt;
    pr = pr->next;
  }
}
template<typename T>
Queue<T>::~Queue()
{ 
  listNode<T> *pr=myBack->next,*pt; 
  while (pr != myBack)
  {
    pt = pr->next;
    delete pr;
    pr = pt;
  }
}
template<typename T>
void Queue<T>::enqueue(const T & item)//添加咯，感觉是除了构造最重要的函数
{ //这里是这样的：先新建一个节点记住myback的next，这样才能保证是个循环的圈~（因为最后这个节点会变成myback）；
  listNode<T> *pr;
  pr = new listNode<T>(NULL, myBack->next);//记住myback的下一个就是第一个的地址；
  myBack->NodeData = item;//把要添加的节点的值赋给当前的最后一个；
  myBack->next = pr;//指向新节点，将是新的myback;
  myBack = pr;//这样myback就后移了
}//其实就是将新节点插在myback前面，而且没有遍历链表。
template<typename T>
bool Queue<T>::empty() const  { return myBack == myBack->next; }//就和刚构造的时候一样，当就剩下一个myback的时候哦就是空了；
template<typename T>
void Queue<T>::dequeue()//删除第一个节点。也就是myback间隔跳了一个，然后哦把跳过的那一个的空间给还了；
{
  listNode<T> *pr;
  try
  {
    if (empty())//先判断是不是空的，空的不能删，给它报错
      throw out_of_range("Queue<>::dequeue() :empty queue");
    else
    {
      pr = myBack->next;//pr记住myback的next（其实就是第一个了），为了跳过第一个有了第二句。。
      myBack->next = pr->next;//跳过了
      delete pr;//还空间
    }
  }
  catch (exception const& ex)//抓异常的
  {
    cerr << "Exception: " << ex.what() << endl;
  }
}
template<typename T>
const T & Queue<T>::front() const
{
  listNode<T> *pr;
  pr = myBack->next;
  try
  {
    if (empty())
      throw out_of_range("Queue<>::dequeue() :empty queue");
    else
      return pr->NodeData;
  }
  catch (exception const& ex)
  {
    cerr << "Exception: " << ex.what() << endl;
  }
}
template<typename T>
void Queue<T>::display() const
{
  listNode<T> *pr=myBack->next;
  if (empty())
  {
    cout << "Queue<>::dequeue() :empty queue\n";
    return;
  }
  while (pr!=myBack)
  {
    cout << pr->NodeData<<" ";
    pr = pr->next;
  }
  cout << endl;
}
template<typename T>
Queue<T> & Queue<T>::operator =(const Queue<T> &or)
{
  Queue<T>::~Queue();
  myBack = new listNode<T>();
  myBack->next = myBack;
  listNode<T> *pr = or.myBack->next, *pt = myBack->next;
  myBack->NodeData = or.myBack->NodeData;
  myBack->next = myBack;
  while (pr != or.myBack)
  {
    pt = new listNode<T>(NULL, myBack->next);
    myBack->NodeData = pr->NodeData;
    myBack->next = pt;
    myBack = pt;
    pr = pr->next;
  }
  return *this;
}

#include"Queue.h"
using namespace std;
int main()
{
  Queue<int> que;
  int i = 1;
  int num;
  srand(unsigned int(time(0)));
  cout << "随机产生的从0~99的数字20个：" << endl;
  for (; i <= 20; i++)
  {
    num = rand() % 100;
    cout << num << " ";
    que.enqueue(num);
  }
  cout << endl<<endl<<endl;
  system("pause");
  que.display();
  system("pause");
  Queue<int> que2(que), que3 = que;
  //que2.display();
  //que3.display();
  //system("pause");
  cout << "开始删除\n";
  while (!que.empty())
  {
    cout << que.front() <<endl;
    que.dequeue();
  }
  cout << endl;
  system("pause");
  que.dequeue();
  system("pause");
  que.display();
  system("pause");
  cout<<que.front();
  system("pause");
  cout << "que2 以及que3 未被删\n";
  que2.display();
  que3.display();
  system("pause");
  return 0;
}