C++链表实现

#pragma once
template <typename T>
class Chain {
private:
	T item;
	Chain<T>* now = this;
	Chain<T>* next;
	Chain<T>* pre;
	Chain<T>* end;
	//this同时也是链表的开始
public:
	//N为链表长度
	static int N;
	Chain() {}
	void push(T a) {
		if (!next)
		{
			now->item = a;
			now->next = new Chain();
			now->next->pre = now;
		}
		else
		{
			now->next = new Chain();
			now->next->item = a;
			now->next->pre = now;
			now = now->next;
		}
		end = now;
		N++;
	}
	T pop() {
		now = end;
		T temp = now->item;
		if (now->pre)
		{
			now = now->pre;
			now->next = nullptr;
			delete now->next;
			end = now;
		}
		else {
			now = nullptr;
			delete now;
		}
		N--;
		return temp;
	}

	//按下表顺序删除特定元素
	void deleteitem(int n) {
		now = this;
		int i = 0;
		while (n != i++) now = now->next;
		Chain* oldnext = now->next;
		Chain* oldnow = now;
		oldnow = nullptr;
		now = now->pre;
		oldnext->pre = now;
		delete oldnow;
		now->next = oldnext;
		N--;
	}
};
template <typename S>
int Chain<S>::N = 0;