C++ STL queue 的实现

求点赞，求关注，求评论
求点赞，求关注，求评论
求点赞，求关注，求评论
求点赞，求关注，求评论
求点赞，求关注，求评论
求点赞，求关注，求评论
求点赞，求关注，求评论
这篇文章很短，直接给代码:

#include <iostream>
using namespace std;
template <class T>class Queue {
protected:
	struct node {
		T data;
		node *next;
	};
	node *head;
	node *tail;
	size_t len;
public:
	Queue() {
		head = NULL;
		tail = NULL;
		len = 0;
	}
	~Queue() {
		node *ptr = NULL;
		while(head != NULL) {
			ptr = head->next;
			delete head;
			head = ptr;
		}
	}
	void push(T var) {
		node *ptr = new node;
		ptr->data = var;
		ptr->next = NULL;
		if(tail != NULL) {
			tail->next = ptr;
		}
		else {
			head = ptr;
		}
		tail = ptr;
		len++;
	}
	void pop() {
		if (len <= 0) {
			abort();
		}
		node *ptr = head->next;
		delete head;
		head = ptr;
		if(head == NULL) {
			tail = NULL;
		}
		len--;
	}
	T front() {
		return head->data;
	}
	T back() {
		return tail->data;
	}
	bool empty() {
		return head == NULL && tail == NULL;
	}
	size_t size() {
		return len;
	}
	void clear() {
		while (len > 0) {
			pop();
		}
	}
};