C++初阶（十四）list

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??走在路上，不忘来时的初心

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一、 list的介绍

1. list是可以在常数范围内在任意位置进行插入和删除的序列式容器，并且该容器可以前后双向迭代。
2. list的底层是双向链表结构，双向链表中每个元素存储在互不相关的独立节点中，在节点中通过指针指向其前一个元素和后一个元素。
3. list与forward_list非常相似：最主要的不同在于forward_list是单链表，只能朝前迭代，已让其更简单高效。
4. 与其他的序列式容器相比(array，vector，deque)，list通常在任意位置进行插入、移除元素的执行效率更好。
5. 与其他序列式容器相比，list和forward_list最大的缺陷是不支持任意位置的随机访问，比如：要访问list的第6个元素，必须从已知的位置(比如头部或者尾部)迭代到该位置，在这段位置上迭代需要线性的时间开销；list还需要一些额外的空间，以保存每个节点的相关联信息(对于存储类型较小元素的大list来说这可能是一个重要的因素)

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二、list的模拟实现

1、list的节点

template<class T>
	struct list_node
	{
		T _data;
		list_node<T>* _prev;
		list_node<T>* _next;

		list_node(const T& x = T())
			:_data(x)
			, _next(nullptr)
			, _prev(nullptr)
		{}
	};

2、list 的迭代器

template<class T, class Ref, class Ptr>
	struct __list_iterator
	{
		typedef list_node<T> Node;
		typedef __list_iterator<T, Ref, Ptr> self;
		Node* _node;

		__list_iterator(Node* node)
			:_node(node)
		{}

		self& operator++()
		{
			_node = _node->_next;
			return *this;
		}

		self& operator--()
		{
			_node = _node->_prev;
			return *this;
		}

		self operator++(int)
		{
			self tmp(*this);
			_node = _node->_next;

			return tmp;
		}

		self operator--(int)
		{
			self tmp(*this);
			_node = _node->_prev;

			return tmp;
		}

		Ref operator*()
		{
			return _node->_data;
		}

		Ptr operator->()
		{
			return &_node->_data;
		}

		bool operator!=(const self& s)
		{
			return _node != s._node;
		}

		bool operator==(const self& s)
		{
			return _node == s._node;
		}
	};

3、list

template<class T>
	class list
	{
		typedef list_node<T> Node;
	public:
		typedef __list_iterator<T, T&, T*> iterator;
		typedef __list_iterator<T, const T&, const T*> const_iterator;
		
		iterator begin()
		{
			return _head->_next;
		}
		iterator end()
		{
			return _head;
		}
		const_iterator begin() const
		{
			return _head->_next;
		}

		const_iterator end() const
		{
			return _head;
		}
		void empty_init()
		{
			_head = new Node;
			_head->_next = _head;
			_head->_prev = _head;
			_size = 0;
		}
		list()
		{
			empty_init();
		}
		list(list<T>& lt)
		{
			empty_init();
			for (auto e : lt)
			{
				push_back(e);
			}
		}
		list<T>& operator=(list<T> lt)
		{
			swap(lt);
			return *this;
		}
		void swap(list<T> lt)
		{
			std::swap(_size, lt._size);

			std::swap(_head, lt._head);
		}
		
		iterator insert(iterator pos, const T& x)
		{
			Node* cur = pos._node;
			Node* newnode = new Node(x);

			Node* prev = cur->_prev;

			prev->_next = newnode;
			newnode->_prev = prev;

			newnode->_next = cur;
			cur->_prev = newnode;
			++_size;

			return iterator(newnode);
		}
		iterator erase(iterator pos)
		{
			Node* cur = pos._node;

			Node* prev = cur->_prev;
			Node* next = cur->_next;
			delete cur;
			prev->_next = next;
			next->_prev = prev;
			--_size;
		}
		size_t size()
		{
			return _size;
		}
		void clear()
		{
			iterator it = begin();
			while (it != end)
			{
				it = erase(it);
			}
		}
		void push_back(const T& x)
		{
			insert(end(), x);
		}
		void push_front(const T& x)
		{
			insert(begin(), x);
		}
		void push_back()
		{
			erase(end());
		}
		void pop_back()
		{

			erase(begin());
		}
		

		
	private:
		Node* _head;
		size_t _size;


	};

4、打印

template<typename Container>
	void print_container(const Container& con)
	{
		typename Container::const_iterator it = con.begin();
		while (it != con.end())
		{
			cout << *it << " ";
			++it;
		}
		cout << endl;
	}
	void test_list()
	{
		list<int> lt;
		lt.push_back(1);
		lt.push_back(2);
		lt.push_back(3);
		lt.push_back(4);
		lt.push_back(5);
	
		print_container(lt);

		list<string> lt1;
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		
		print_container(lt1);

		vector<string> v;
		v.push_back("222222222222222222222");
		v.push_back("222222222222222222222");
		v.push_back("222222222222222222222");
		v.push_back("222222222222222222222");
		
		print_container(v);
		
	}
}
int main()
{
	bit::test_list();
	return 0;
}

5、完整代码

#include<iostream>
#include<string>
#include<vector>
using namespace std;
namespace bit
{
	template<class T>
	struct list_node
	{
		T _data;
		list_node<T>* _prev;
		list_node<T>* _next;

		list_node(const T& x = T())
			:_data(x)
			, _next(nullptr)
			, _prev(nullptr)
		{}
	};
	template<class T, class Ref, class Ptr>
	struct __list_iterator
	{
		typedef list_node<T> Node;
		typedef __list_iterator<T, Ref, Ptr> self;
		Node* _node;

		__list_iterator(Node* node)
			:_node(node)
		{}

		self& operator++()
		{
			_node = _node->_next;
			return *this;
		}

		self& operator--()
		{
			_node = _node->_prev;
			return *this;
		}

		self operator++(int)
		{
			self tmp(*this);
			_node = _node->_next;

			return tmp;
		}

		self operator--(int)
		{
			self tmp(*this);
			_node = _node->_prev;

			return tmp;
		}

		Ref operator*()
		{
			return _node->_data;
		}

		Ptr operator->()
		{
			return &_node->_data;
		}

		bool operator!=(const self& s)
		{
			return _node != s._node;
		}

		bool operator==(const self& s)
		{
			return _node == s._node;
		}
	};
	template<class T>
	class list
	{
		typedef list_node<T> Node;
	public:
		typedef __list_iterator<T, T&, T*> iterator;
		typedef __list_iterator<T, const T&, const T*> const_iterator;
		
		iterator begin()
		{
			return _head->_next;
		}
		iterator end()
		{
			return _head;
		}
		const_iterator begin() const
		{
			return _head->_next;
		}

		const_iterator end() const
		{
			return _head;
		}
		void empty_init()
		{
			_head = new Node;
			_head->_next = _head;
			_head->_prev = _head;
			_size = 0;
		}
		list()
		{
			empty_init();
		}
		list(list<T>& lt)
		{
			empty_init();
			for (auto e : lt)
			{
				push_back(e);
			}
		}
		list<T>& operator=(list<T> lt)
		{
			swap(lt);
			return *this;
		}
		void swap(list<T> lt)
		{
			std::swap(_size, lt._size);

			std::swap(_head, lt._head);
		}
		
		iterator insert(iterator pos, const T& x)
		{
			Node* cur = pos._node;
			Node* newnode = new Node(x);

			Node* prev = cur->_prev;

			prev->_next = newnode;
			newnode->_prev = prev;

			newnode->_next = cur;
			cur->_prev = newnode;
			++_size;

			return iterator(newnode);
		}
		iterator erase(iterator pos)
		{
			Node* cur = pos._node;

			Node* prev = cur->_prev;
			Node* next = cur->_next;
			delete cur;
			prev->_next = next;
			next->_prev = prev;
			--_size;
		}
		size_t size()
		{
			return _size;
		}
		void clear()
		{
			iterator it = begin();
			while (it != end)
			{
				it = erase(it);
			}
		}
		void push_back(const T& x)
		{
			insert(end(), x);
		}
		void push_front(const T& x)
		{
			insert(begin(), x);
		}
		void push_back()
		{
			erase(end());
		}
		void pop_back()
		{

			erase(begin());
		}
		

		
	private:
		Node* _head;
		size_t _size;


	};

	template<typename Container>
	void print_container(const Container& con)
	{
		typename Container::const_iterator it = con.begin();
		while (it != con.end())
		{
			cout << *it << " ";
			++it;
		}
		cout << endl;
	}
	
	void test_list()
	{
		list<int> lt;
		lt.push_back(1);
		lt.push_back(2);
		lt.push_back(3);
		lt.push_back(4);
		lt.push_back(5);
	
		print_container(lt);

		list<string> lt1;
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		lt1.push_back("1111111111111");
		
		print_container(lt1);

		vector<string> v;
		v.push_back("222222222222222222222");
		v.push_back("222222222222222222222");
		v.push_back("222222222222222222222");
		v.push_back("222222222222222222222");
		
		print_container(v);
		
	}
}
int main()
{
	bit::test_list();
	return 0;
}

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