模拟实现 ListIterator类

#include<iostream>using namespace std;template <class T>struct ListNode{    ListNode(const T& data = T())    : _pNext(NULL)    , _pPre(NULL)    , _data(data)    {}    ListNode<T>* _pNext;// 模板类下类型表示为：ListNode<T>    ListNode<T>* _pPre;    T _data;};#if 1  //对一些基本操作的重载。(++,--，!=,*,->)// 参考下list的迭代器template <class T>class ListIterator{    typedef ListNode<T>* PNode;    typedef ListNode<T> Node;    typedef ListIterator Self;public:    ListIterator()        : _pCur(NULL)    {}    ListIterator(PNode pCur)        : _pCur(pCur)    {}    ListIterator(const Self& s)        : _pCur(s._pCur)    {}    Self& operator++()    {        _pCur = _pCur->_pNext;        return *this;    }    Self operator++(int)    {        Self temp(*this);        _pCur = _pCur->_pNext;        return temp;    }    Self& operator--()    {        _pCur = _pCur->_pPre;        return *this;    }    Self operator--(int)    {        Self temp(*this);        _pCur = _pCur->_pPre;        return *this;    }    bool operator!=(const Self& s)    {        return _pCur != s._pCur;    }    bool operator==(const Self& s)    {        return _pCur == s._pCur;    }    T& operator*()    {        return _pCur->_data;    }    T* operator->()    {        return &(_pCur->_data);    }private:    PNode _pCur;};#endiftemplate<class T>class List{    typedef ListNode<T> Node;    typedef Node* PNode;public:    typedef ListIterator<T> Iterator;public:    List()//无参时，建立链表的头结点（空链表）    {         CreateListHead();//建立链表的头结点    }    List(T* array, size_t size)//有参时，传类型，传个数，传元素（以数组的方式传）    {        CreateListHead();//先有一个表头结点        for (int i = 0; i < size; i++)//不用memcpy函数：会产生浅拷贝        {            PushBack(array[i]);//尾插元素        }    }    List(const List& l)//拷贝构造函数：深拷贝方式    {        _phead = new Node;        PNode ptail = l->pNext;        while (ptail == l)        {            PushBack(ptail->data);            ptail = ptail->pNext;        }    }    List& operator=(const List& l)//赋值运算符重载    {        if (this == &l)        {            return *this;        }        _phead = new Node;        PNode ptail = l->pNext;        while (ptail == l)        {            PushBack(ptail->data);            ptail = ptail->pNext;        }    }    ~List()    {        Clear();//清空链表中的元素，表头结点还在        delete _pHead;        _pHead = NULL;    }        ///////////////////////////////////////////////    Iterator Begin()//获取第一个元素地址    {        return Iterator(_pHead->_pNext);    }    Iterator End()//获取表头元素地址    {        return Iterator(_pHead);    }    void PushBack(const T& data)    {        PNode ptail = _pHead->_pPre;        PNode pNewNode = new Node(data);        ptail->_pNext = pNewNode;        pNewNode->_pNext = _pHead;        pNewNode->_pPre = ptail;        _pHead->_pPre = pNewNode;    }    void PopBack()    {        PNode ptail = _pHead->_pPre;        ptail->_pPre->_pNext =_pHead;        _pHead->_pPre = ptail->_pPre;        delete ptail;    }    void PushFront(const T& data)    {        PNode ptail = new Node(data);        ptail->_pNext = _pHead->_pNext;        -pHead->_pNext->_pPre = ptail;        ptail->_pPre = _pHead;        _pHead->_pNext = ptail;    }    void PopFront()    {        if (_pHead->_pNext == _phead)            return;        else        {            PNode ptail = _pHead->_pNext;            _pHead->_pNext = ptail->_pNext;            ptail->_pNext->pPre = _pHead;            delete ptail;        }    }    PNode Insert(PNode pos, const T& data)    {        PNode ptail = pos->_pPre;        PNode pNewNode = new Node(data);        pNewNode->_pNext = ptail;        ptail->_pPre = pNewNode;        pos->_pNext = pNewNode;        pNewNode->_pPre = pos;    }    PNode Erase(PNode pos)    {        pos->_pPre->_pNext = pos->_pNext;        pos->_pNest->pPre = pos->_pPre;        delete pos;    }    size_t Size()    {        int count = 0;        PNode ptail = _pHead->_pNext;        while (ptail != _pHead)        {            count++;            ptail = ptail->_pNext;        }        return count;    }        // 将链表中的结点清空    void Clear()    {        PNode ptail = _pHead->_pNext;        while (ptail != _pHead)        {            _pHead->_pNext = ptail->_pNext;            delete ptail;            ptail = _pHead->_pNext;        }        ptail->_pPre = _pHead;    }    bool Empty()const    {        return _pHead->_pNext - _pHead;    }private:    void CreateListHead()    {        _pHead = new Node;        _pHead->_pNext = _pHead;        _pHead->_pPre = _pHead;    }private:    PNode _pHead;};template <class Iterator>Iterator Find(Iterator start, Iterator finish,const T& data){    while (start != finish)    {        if (*start == data)            return start;        ++start;    }    return start;}int main(void){    size_t i;    List<int> l1;    l1.PushBack(1);    l1.PushBack(2);    l1.PushBack(3);    l1.PushBack(4);    l1.PopBack();    //打印元素    List<int>::Iterator it = l1.Begin();    while (l1.End() != it)    {        cout << *it << "  ";        ++it;    }    cout<<endl;    i = l1.Size();    cout << l1.Empty() << endl;    cout << i << endl;    l1.Clear();    l1.~List();    //此函数后的调用无效；对象不存在；会崩溃    cout << l1.Empty() << endl;    i = l1.Size();    cout << i << endl;    return 0;}