c++ 实现双链表

#include <iostream>using namespace std;typedef int DataType;struct Node{Node(const DataType& data):_data(data),_pre(NULL),_next(NULL){}DataType _data;Node* _pre;Node* _next;};class List{public:explicit List():_pHead(NULL),_pTail(NULL),_size(0){}    friend ostream& operator <<(ostream& cout,const List l){Node* pTemp = l._pHead;while (pTemp){cout<<pTemp->_data<<"->";pTemp = pTemp->_next;}cout<<"NULL"<<endl;return cout;}List(size_t n, const DataType& data = DataType())   //创建一个由n个data构成的节点{if (n>0){_size = 1;_pHead =  new Node(data);Node* pTemp = _pHead;while (--n){pTemp ->_next = new Node (data);pTemp ->_next ->_pre = pTemp ;pTemp = pTemp ->_next ;_size ++;}_pTail = pTemp;}}List(const List& l):_pHead(NULL),_pTail(NULL),_size(){_CopyList(l._pHead);}List& operator=(const List& l){if (this != &l){List ltemp(l);return ltemp;}}~List(){    _DestroyList();}size_t Size()const{return _size;}bool Empty()const{return (0 == _size);}Node& Front(){return *_pHead;}const Node& Front()const{return *_pHead;}Node& Back(){return *_pTail;}const Node& Back()const{return *_pTail;}void Assign(size_t n, const DataType& data)  //为list重新开辟空间并赋值，n个datatype类型的data{if (n<0)return ;_size = 1;_pHead =  new Node(data);Node* pTemp = _pHead;while (--n){pTemp ->_next = new Node (data);pTemp ->_next ->_pre = pTemp ;pTemp = pTemp ->_next ;_size ++;}_pTail = pTemp;}void Assign(Node* first, Node* second)  //复制一个节点到另一个节点的链表给一个新空间{if (NULL == first || NULL == second)return ;_pHead = new Node(first ->_data);         Node* pTemp = _pHead; _size = 1 ; while (first != second) { first = first->_next; pTemp ->_next = new Node(first->_data); pTemp ->_next ->_pre = pTemp; pTemp = pTemp ->_next;             _size ++; } _pTail = pTemp;}void PushBack(const DataType& data)  //尾插{ if (NULL == _pHead){_pHead = new Node (data);_pTail = _pHead ;_size = 1;}else {_pTail ->_next = new Node(data);_pTail ->_next ->_pre = _pTail;_pTail = _pTail->_next;_size ++ ;}}void PopBack()   //尾删{if (NULL == _pHead)return;else  if (_size == 1){delete (_pHead);_pHead = NULL;_pTail = NULL;_size = 0;}else {_pTail = _pTail ->_pre;_pTail ->_next = NULL;_size --;}}void PushFront(const DataType& data)  //头插{if (NULL == _pHead){_pHead = new Node (data);_pTail = _pHead ;_size = 1;}else {_pHead ->_pre = new Node(data);_pHead ->_pre ->_next = _pHead;_pHead = _pHead->_pre;_size ++ ;}}void PopFront(){if (NULL == _pHead)return;else  if (_size == 1){delete (_pHead);_pHead = NULL;_pTail = NULL;_size = 0;}else {_pHead = _pHead ->_next;_pHead ->_pre = NULL;_size --;}}Node* Find(const DataType& data){Node* pTemp = _pHead;while (pTemp){if (pTemp->_data == data)return pTemp;pTemp = pTemp->_next;}return NULL;}void Insert(Node* pos, const DataType& data){if (NULL == pos)return;else if(_pHead == pos){pos = new Node(data);pos ->_next = _pHead;_pHead ->_pre = pos;_pHead = pos;_size ++;}else{           Node* pTemp = new Node(data);   pos->_pre ->_next = pTemp;   pTemp ->_pre = pos->_pre;   pTemp ->_next = pos;   pos ->_pre = pTemp;   _size ++;}}void Erase(Node* pos){if (NULL == pos)return;if (pos==_pHead)PopFront();else if (pos == _pTail)PopBack();else{pos ->_pre->_next = pos ->_next;pos ->_next ->_pre = pos ->_pre;_size --;}}private:void _CopyList(Node* pos){if (NULL == pos)return ;_pHead = new Node(pos ->_data);_size = 1;Node* pTemp = _pHead ;while (pos ->_next){pos = pos ->_next;pTemp ->_next = new Node(pos->_data);pTemp ->_next ->_pre = pTemp;pTemp = pTemp ->_next;_size ++;}_pTail = pTemp;}void _DestroyList(){if (NULL == _pHead)return ;while (_pTail != _pHead){_pTail = _pTail ->_pre;delete (_pTail ->_next);_pTail ->_next = NULL;}delete _pHead;_pHead = NULL;_pTail = NULL;_size = 0;}private:Node* _pHead;Node* _pTail;size_t _size;};int main(){List l1(5,1);//List l2(l1);List l2;l2.Assign(&l1.Front(),&l1.Back());    List l3 (l2);l3.PushBack(2);l3.PopFront();l3.PopFront();l3.PopFront();l3.PushBack(5);l3.PushBack(6);l3.PushBack(3);l3.PushBack(4);Node* ret = l3.Find(6);l3.Erase(ret);List l4 = l3;cout<<l4;return  0;}