C++ List

#include
#include
using namespace std;

typedef int DataType;

struct Listnode
{
	DataType _data;
	Listnode* _next;
	Listnode* _prev;


	Listnode()
		:_data(DataType())
		,_next(NULL)
		,_prev(NULL)
	{}
};


class List
{
	typedef Listnode Node;
public:
	
	List()//构造函数
	{
		_head = new Node;
		_head->_next = _head;
		_head->_prev = _head;
	}

	~List()//析构函数
	{
		
		Node *cur = _head->_next;
		while (cur != _head)
		{
			Node *next = cur->_next;
			delete cur;
			cur = next;
		}

		delete _head;
		_head = NULL;
		
	}


	List(const List& l)//拷贝构造
	{
		_head = new Node;
		_head->_next = _head;
		_head->_prev = _head;

		Node* cur = l._head->_next;
		while (cur != l._head)
		{
			PushBack(cur->_data);
			cur = cur->_next;
		}
	}


	List& operator=(const List& l)//赋值运算符重载
	{
		List tmp(l);
		swap(_head, tmp._head);
		return *this;
	}

	void PushBack(DataType x)//尾插
	{
		Insert(_head, x);
	}


	void PopBack()//尾删
	{
		Erase(_head->_prev);
	}


	void PushFront(DataType x)//头插
	{
		Insert(_head->_next, x);
	}


	void PopFront()//头删
	{
		Erase(_head->_next);
	}


	void Insert(Node* pos, DataType x)//在pos前插入一个节点，值为x
	{
		Node *prev = pos->_prev;
		Node *newnode = new Node;

		newnode->_data = x;
		newnode->_prev = prev;
		prev->_next = newnode;
		newnode->_next = pos;
		pos->_prev = newnode;

	}
	void Erase(Node* pos)//删除pos节点
	{
		assert(pos != _head);
		Node* prev = pos->_prev;
		Node* next = pos->_next;

		delete pos;
		prev->_next = next;
		next->_prev = prev;
	}


	void print()//输出链表
	{
		Node* cur = _head->_next;
		while (cur != _head)
		{
			cout << cur->_data << "  ";
			cur = cur->_next;
		}
		cout << endl;

	}


	size_t size()//求长
	{
		size_t i = 0;
		Node* cur = _head->_next;
		while (cur != _head)
		{
			i++;
			cur = cur->_next;
		}
		return i;
	}
	bool Empty()//判空
	{
		return _head->_next == _head;
	}


private:
	Node* _head;
};