本蒟蒻这两天在用指针实现链表，可是搞不好清空操作，求帮助！
Code：

#ifndef _list_H
#define _list_H
template<typename T>
void Free(T*p){delete p;p=nullptr;return;}
template<typename T>
class Node{
	public:
		Node *pre,*next;
		T val;
		Node(){}
		Node(T v,Node*p=nullptr,Node*n=nullptr){val=v,pre=p,next=n;}
};
template<typename T>
class _list{
	private:
		Node<T> *head,*tail,*newnode,*cur;
	public:
		void clear();
		void create(T v);
		void push_front(T v);
		void push_back(T v);
		void pop_front();
		void pop_back();
		T front();
		T back();
		int size();
		bool empty();
		auto begin();
		auto end();
};
template<typename T>
void _list<T>::clear(){
	
	return;
}
template<typename T>
void _list<T>::create(T v){
	head=new Node<T>(v);
	tail=new Node<T>(v);
	head->next=tail;tail->pre=head;
	return;
}
template<typename T>
void _list<T>::push_front(T v){
	newnode=new Node<T>(v,head,head->next);
	head->next->pre=newnode;head->next=newnode;
	return;
}
template<typename T>
void _list<T>::push_back(T v){
	newnode=new Node<T>(v,tail->pre,tail);
	tail->pre->next=newnode;tail->pre=newnode;
	return;
}
template<typename T>
void _list<T>::pop_front(){
	if(empty()) return;
	cur=head->next;
	head->next->next->pre=head;head->next=head->next->next;
	Free(cur);
	return;
}
template<typename T>
void _list<T>::pop_back(){
	if(empty()) return;
	cur=tail->pre;
	tail->pre->pre->next=tail;tail->pre=tail->pre->pre;
	Free(cur);
	return;
}
template<typename T>
T _list<T>::front(){return head->next->val;}
template<typename T>
T _list<T>::back(){return tail->pre->val;}
template<typename T>
int _list<T>::size(){
	if(empty()) return 0;
	int s=0;cur=head;
	while(cur!=tail) ++s,cur=cur->next;
	return s-1;
}
template<typename T>
bool _list<T>::empty(){return (head==nullptr&&tail==nullptr)||head->next==tail;}
template<typename T>
auto _list<T>::begin(){return head->next;}
template<typename T>
auto _list<T>::end(){return tail;}
#endif