C++实现双向链表

#include<iostream>

using namespace std;
typedef int DataType;

struct Node
{
Node(const DataType&d)
:_data(d)
, _next(NULL)
, _prev(NULL)
{}
Node*_next;
Node*_prev;
DataType _data;
};
class DList
{
friend ostream&operator<<(ostream&os, DList& d);
public:
DList()
:_head(NULL)
, _tail(NULL)
{}
~DList()
{
Node*cur=_head;
while (cur)
{
Node*del = cur;
cur = cur->_next;
delete del;

}
}
public:
void PushBack(const DataType&d);//尾插
void PopBack();//尾删
void PushFront(const DataType&d);//头插
void PopFront();//头删2

private:
Node*_head;
Node*_tail;
};
ostream&operator<<(ostream&os, DList& d)
{
Node* cur = d._head;
while (cur)
{
cout << cur->_data << "<=>";
cur = cur->_next;
}
cout << "over" << endl;
return os;
}
void DList::PushBack(const DataType&d)//尾插
{
Node*newNode = new Node(d);
if (_head == NULL)
{
_head = newNode;
_tail = newNode;
}
else
{
_tail->_next = newNode;
newNode->_prev = _tail;
_tail = newNode;
}
}
void DList::PopBack()//尾删
{
if (_head == NULL)//没节点
{
return;
}
if (_head == _tail)//一个节点
{
delete _tail;
_head = NULL;
_tail = NULL;
return;
}
//多节点
_tail = _tail->_prev;
delete _tail->_next;
_tail->_next = NULL;
}
void DList::PushFront(const DataType&d)//头插
{
Node*newNode = new Node(d);
if (_head == NULL)
{
_head = newNode;
_tail = newNode;
}
else
{
newNode->_next = _head;
_head->_prev = newNode;
_head = newNode;
}
}
void DList::PopFront()//头删
{
if (_head == NULL)
{
return;
}
if (_head == _tail)
{
delete _tail;
_tail = NULL;
_head = NULL;
return;
}
Node*del = _head;
_head = _head->_next;
_head->_prev = NULL;
delete del;

}
Node*DList::Find(const DataType&d)//查找
{
Node*cur = _head;
while (cur)
{
if (cur->_data == d)
{
return cur;
}
cur = cur->_next;
}
return NULL;
}
void DList:: Insert(Node* pos, const DataType&d)//插入
{
Node*newNode = new Node(d);
if (pos == _tail)
{
_tail->_next = newNode;
newNode->_prev = _tail;
_tail = newNode;
}
else
{
newNode->_next = pos->_next;
pos->_next->_prev = newNode;
newNode->_prev = pos;
pos->_next = newNode;
}
}