C++ list类 - 技术栈

1.list的介绍及使用

1.1list的文档介绍：

cplusplus.com/reference/list/list/?kw=list。

同样我们也可以借助文档来学习：list - C++ Reference。

1.2list的使用

注意这里的list为带头双向循环链表。

1.2.1 构造函数

cplusplus.com/reference/list/list/list/

常用的：

1.2.2 list iterator的使用

基本和vector、string迭代器的使用类似。

我们观察文档可以发现list的迭代器是一个双向迭代器，这似乎和我们之前学习的vector和string类的迭代器有所不同。

list的Member types

vector的Member types

vector为随机迭代器，这里我们就需要做一下比较和区分。

【注意】

begin与end为正向迭代器，对迭代器执行++操作，迭代器向后移动。
rbegin(end)与rend(begin)为反向迭代器，对迭代器执行++操作，迭代器向前移动。

1.2.3 list capacity

1.2.4 list element access

1.2.5 list modifiers

list中还有一些操作，需要用到时大家可参阅list的文档说明。

1.2.6 list的迭代器失效

前面说过可将迭代器暂时理解成类似于指针，迭代器失效即迭代器所指向的节点的无效，即该节点被删除了 。因为list的底层结构为带头结点的双向循环链表 ，因此在list中进行插入时是不会导致list的迭代器失效的，只有在 删除时才会失效 ，并且失效的只是指向被删除节点的迭代器，其他迭代器不会受到影响。

cpp 复制代码

#include <iostream>
#include <list>

using namespace std;

void TestListIterator1()
{
	int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
	list<int> l(array, array + sizeof(array) / sizeof(array[0]));
	auto it = l.begin();
	while (it != l.end())
	{
		// erase()函数执行后，it所指向的节点已被删除，因此it无效，在下一次使用it时，必须先给其赋值
        l.erase(it);
		++it;
	}
}

// 改正
void TestListIterator2()
{
	int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
	list<int> l(array, array + sizeof(array) / sizeof(array[0]));
	auto it = l.begin();
	while (it != l.end())
	{
		l.erase(it++); // it = l.erase(it);
	}
}

int main()
{
	TestListIterator2();
	return 0;
}

1.2.7 test.cpp

cpp 复制代码

#include<iostream>
#include<algorithm>
#include<list>
#include<vector>
using namespace std;

void test_list1()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);

	list<int>::iterator it = lt.begin();
	while (it != lt.end())
	{
		cout << *it << " ";
		++it;
	}
	cout << endl;

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	//不支持
	/*it = lt.begin();
	lt.erase(it + 3);*/

	 //不支持，要求随机迭代器
	//sort(lt.begin(), lt.end());

	string s("dadawdfadsa");//string 随机迭代器
	cout << s << endl;
	sort(s.begin(), s.end());
	cout << s << endl;
}

struct A
{
public:
	A(int a1 = 1, int a2 = 1)
		:_a1(a1)
		, _a2(a2)
	{
		cout << "A(int a1 = 1, int a2 = 1)" << endl;
	}

	A(const A& aa)
		:_a1(aa._a1)
		, _a2(aa._a2)
	{
		cout << "A(const A& aa)" << endl;
	}

	int _a1;
	int _a2;
};

void test_list2()
{
	list<int> lt1;
	lt1.push_back(1);
	//和push_back类似
	lt1.emplace_back(2);
	lt1.emplace_back(3);
	lt1.emplace_back(4);
	for (auto e : lt1)
	{
		cout << e << " ";
	}
	cout << endl;

	list<A> lt2;
	A aa1(1, 1);
	lt2.push_back(aa1);
	lt2.push_back(A(2, 2));

	//push_back不支持
	//lt2.push_back(3, 3);

	lt2.emplace_back(aa1);
	lt2.emplace_back(A(2, 2));
	cout << endl;
	//emplace_back支持直接传构造A对象的参数 不用拷贝构造 可以提高效率
	lt2.emplace_back(3, 3);
}
//运行结果：
//1 2 3 4
//A(int a1 = 1, int a2 = 1)
//A(const A & aa)
//A(int a1 = 1, int a2 = 1)
//A(const A & aa)
//A(const A & aa)
//A(int a1 = 1, int a2 = 1)
//A(const A & aa)
//
//A(int a1 = 1, int a2 = 1)

void test_list3()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);
	lt.push_back(5);
	lt.push_back(6);

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	auto it = lt.begin();
	int k = 3;
	while (k--)
	{
		++it;
	}

	lt.insert(it, 30);

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	int x = 0;
	cin >> x;
	it = find(lt.begin(), lt.end(), x);
	if (it != lt.end())
	{
		lt.erase(it);
	}

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;
}

void test_list4()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(20);
	lt.push_back(3);
	lt.push_back(5);
	lt.push_back(4);
	lt.push_back(5);
	lt.push_back(6);

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	//升序
	lt.sort();
	//降序 - 传仿函数
	less<int> ls;
	greater<int> gt;
	lt.sort(gt);
	lt.sort(greater<int>());

	lt.reverse();
	reverse(lt.begin(), lt.end());

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	std::list<double> first, second;

	first.push_back(3.1);
	first.push_back(2.2);
	first.push_back(2.9);

	second.push_back(3.7);
	second.push_back(7.1);
	second.push_back(1.4);

	first.sort();
	for (auto e : first)
	{
		cout << e << " ";
	}
	cout << endl;

	second.sort();
	for (auto e : second)
	{
		cout << e << " ";
	}
	cout << endl;

	//把second里面的数据归并到frist second里面的数据清空
	first.merge(second);
	for (auto e : first)
	{
		cout << e << " ";
	}
	cout << endl;
	for (auto e : second)
	{
		cout << e << " ";
	}
	cout << endl;
}

void test_list5()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(20);
	lt.push_back(3);
	lt.push_back(5);
	lt.push_back(5);
	lt.push_back(4);
	lt.push_back(5);
	lt.push_back(6);

	lt.sort();
	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	//去重
	lt.unique();
	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;
}

void test_list6()
{
	// 一个链表节点转移给另一个链表
	list<int> mylist1, mylist2;
	list<int>::iterator it;

	// set some initial values:
	for (int i = 1; i <= 4; ++i)
		mylist1.push_back(i);      // mylist1: 1 2 3 4

	for (int i = 1; i <= 3; ++i)
		mylist2.push_back(i * 10); // mylist2: 10 20 30

	it = mylist1.begin();
	++it;                         // points to 2

	//splice : Transfer elements from list to list
	mylist1.splice(it, mylist2); // mylist1: 1 10 20 30 2 3 4
	// mylist2 (empty)
	// "it" still points to 2 (the 5th element


    // 调整当前链表节点的顺序
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);
	lt.push_back(5);
	lt.push_back(6);
	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	int x = 0;
	cin >> x;
	it = find(lt.begin(), lt.end(), x);
	if (it != lt.end())
	{
		//lt.splice(lt.begin(), lt, it);
		lt.splice(lt.begin(), lt, it, lt.end());
		//把it到lt.end() 内的值 转移到lt.begin()

	}

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;
}
//输入4
//运行结果：
//1 2 3 4 5 6
//4
//4 5 6 1 2 3


//排序效率测试
void test_op1()
{
	srand(time(0));
	const int N = 1000000;

	list<int> lt1;
	vector<int> v;

	for (int i = 0; i < N; ++i)
	{
		auto e = rand() + i;
		lt1.push_back(e);
		v.push_back(e);
	}

	int begin1 = clock();
	// 排序
	sort(v.begin(), v.end());
	int end1 = clock();

	int begin2 = clock();
	lt1.sort();
	int end2 = clock();

	printf("vector sort:%d\n", end1 - begin1);
	printf("list sort:%d\n", end2 - begin2);
}

//运行结果：
//vector sort : 296
//list sort : 506
void test_op2()
{
	srand(time(0));
	const int N = 1000000;

	list<int> lt1;
	list<int> lt2;

	for (int i = 0; i < N; ++i)
	{
		auto e = rand() + i;
		lt1.push_back(e);
		lt2.push_back(e);
	}

	int begin1 = clock();
	// 拷贝vector
	vector<int> v(lt2.begin(), lt2.end());

	// 排序
	sort(v.begin(), v.end());

	// 拷贝回lt2
	lt2.assign(v.begin(), v.end());

	int end1 = clock();

	int begin2 = clock();
	lt1.sort();
	int end2 = clock();

	printf("list copy vector sort copy list sort:%d\n", end1 - begin1);
	printf("list sort:%d\n", end2 - begin2);
}
//运行结果：
//list copy vector sort copy list sort : 543
//list sort : 572

int main()
{
	test_list6();
	//test_op2();
	return 0;
}

2.list的模拟实现

我们在之前数据结构部分学习过双链表的内容，所以实现起来也不算太难。数据结构之顺序表和链表-CSDN博客

list.h

cpp 复制代码

#pragma once
#include<assert.h>

namespace sy
{
	//定义节点
	template<class T>
	struct list_node
	{
		T _data;
		list_node<T>* _next;
		list_node<T>* _prev;

		//使用T的默认构造 const T& data = T()
		list_node(const T& data = T())
			: _data(data)
			, _next(nullptr)
			, _prev(nullptr)
		{}
	};

	//list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;


		//就是指针
		list_iterator(Node* node)
			:_node(node)
		{}

		//类似指针的解引用
		Ref operator*()
		{
			return _node->_data;
		}

		//类似指针的指向
		Ptr operator->()
		{
			return &_node->_data;
		}

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

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

		Self operator++(int)//后置
		{
			Self tmp(*this);
			_node = _node->_next;

			return tmp;
		}

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

			return tmp;
		}

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

		bool operator==(const Self& s) const
		{
			return _node == s._node;
		}
	};
	
	//list反向迭代器 
	template<class T, class Ref, class Ptr>
	struct reverse_list_iterator
	{
		typedef list_node<T> Node;
		typedef reverse_list_iterator<T, Ref, Ptr> Self;
		Node* _node;

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

		//类似指针的解引用
		Ref operator*()
		{
			return _node->_data;
		}

		//类似指针的指向
		Ptr operator->()
		{
			return &_node->_data;
		}

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

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

		Self operator++(int)//后置
		{
			Self tmp(*this);
			_node = _node->_prev;

			return tmp;
		}

		Self& operator--(int)
		{
			Self tmp(*this);
			_node = _node->_next;

			return tmp;
		}

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

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


	//写一个const_iterator比较冗余
	/*template<class T>
	struct list_const_iterator
	{
		typedef list_node<T> Node;
		typedef list_const_iterator<T> Self;
		Node* _node;

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

		const T& operator*()
		{
			return _node->_data;
		}

		const T* operator->()
		{
			return &_node->_data;
		}

		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;
		}

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

		bool operator==(const Self& s) const
		{
			return _node == s._node;
		}
	};*/
	

	template<class T>
	class list
	{
		typedef list_node<T> Node;
	public:
		/*typedef list_iterator<T> iterator;
		typedef list_const_iterator<T> const_iterator;*/

		typedef list_iterator<T, T&, T*> iterator;
		typedef list_iterator<T, const T&, const T*> const_iterator;

		typedef reverse_list_iterator<T, T&, T*> Reverse_iterator;
		typedef reverse_list_iterator<T, const T&, const T*> const_reverse_list_iterator;

		iterator begin()
		{
			return _head->_next;
		}

		iterator end()
		{
			return _head;
		}
		Reverse_iterator rbegin()
		{
			return _head->_prev;
		}
		Reverse_iterator rend()
		{
			return _head;
		}
		const_iterator begin() const
		{
			return _head->_next;
		}

		const_iterator end() const
		{
			return _head;
		}

		void empty_init()
		{
			//双向循环链表
			_head = new Node;
			_head->_next = _head;
			_head->_prev = _head;
			_size = 0;
		}

		list()
		{
			empty_init();
		}

		//初始化列表构造
		list(initializer_list<T> il)
		{
			empty_init();
			for (auto& e : il)
			{
				push_back(e);
			}
		}

		// lt2(lt1)
		list(const list<T>& lt)
		{
			empty_init();

			for (auto& e : lt)
			{
				push_back(e);
			}
		}

		// lt1 = lt3
		list<T>& operator=(list<T> lt)
		{
			swap(lt);
			return *this;
		}

		~list()
		{
			clear();
			delete _head;
			_head = nullptr;
		}

		void clear()
		{
			auto it = begin();
			while (it != end())
			{
				it = erase(it);
			}
		}

		void swap(list<T>& lt)
		{
			std::swap(_head, lt._head);
			std::swap(_size, lt._size);
		}

		void push_back(const T& x)
		{
			/*Node* newnode = new Node(x);
			Node* tail = _head->_prev;

			tail->_next = newnode;
			newnode->_prev = tail;
			newnode->_next = _head;
			_head->_prev = newnode;

			++_size;*/

			insert(end(), x);
		}

		void push_front(const T& x)
		{
			insert(begin(), x);
		}

		iterator insert(iterator pos, const T& x)
		{
			Node* cur = pos._node;
			Node* prev = cur->_prev;
			Node* newnode = new Node(x);

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

			++_size;

			return newnode;
		}

		void pop_back()
		{
			erase(--end());
		}

		void pop_front()
		{
			erase(begin());
		}

		iterator erase(iterator pos)
		{
			assert(pos != end());

			Node* prev = pos._node->_prev;
			Node* next = pos._node->_next;

			prev->_next = next;
			next->_prev = prev;
			delete pos._node;

			--_size;

			return next;
		}

		size_t size() const
		{
			return _size;
		}

		bool empty() const
		{
			return _size == 0;
		}
	private:
		Node* _head;
		size_t _size;
	};

	struct AA
	{
		int _a1 = 1;
		int _a2 = 1;
	};

	// 按需实例化
	// T* const ptr1
	// const T* ptr2
	//遍历各种容器 
	template<class Container>
	void print_container(const Container& con)
	{
		// const iterator -> 迭代器本身不能修改
		// const_iterator -> 指向内容不能修改
		typename Container::const_iterator it = con.begin();//这里如果不加typename告诉编译器这是类型会报错
		//auto it = con.begin();
		while (it != con.end())
		{
			cout << *it << " ";
			++it;
		}
		cout << endl;

		//or
		for (auto e : con)
		{
			cout << e << " ";
		}
		cout << endl;
	}

	void test_list1()
	{
		list<int> lt;
		lt.push_back(1);
		lt.push_back(2);
		lt.push_back(3);
		lt.push_back(4);

		list<int>::iterator it = lt.begin();
		while (it != lt.end())
		{
			*it += 10;

			cout << *it << " ";
			++it;
		}
		cout << endl;

		for (auto e : lt)
		{
			cout << e << " ";
		}
		cout << endl;
		print_container(lt);

		list<AA> lta;
		lta.push_back(AA());
		lta.push_back(AA());
		lta.push_back(AA());
		lta.push_back(AA());
		list<AA>::iterator ita = lta.begin();
		while (ita != lta.end())
		{
			//cout << (*ita)._a1 << ":" << (*ita)._a2 << endl;
			// 特殊处理，本来应该是两个->才合理，为了可读性，省略了一个->
			cout << ita->_a1 << ":" << ita->_a2 << endl;
			cout << ita.operator->()->_a1 << ":" << ita.operator->()->_a2 << endl;

			++ita;
		}
		cout << endl;
	}

	void test_list2()
	{
		list<int> lt;
		lt.push_back(1);
		lt.push_back(2);
		lt.push_back(3);
		lt.push_back(4);

		// insert以后迭代器不失效
		list<int>::iterator it = lt.begin();
		lt.insert(it, 10);
		*it += 100;

		print_container(lt);

		// erase以后迭代器失效
		// 删除所有的偶数
		it = lt.begin();
		while (it != lt.end())
		{
			if (*it % 2 == 0)
			{
				it = lt.erase(it);
			}
			else
			{
				++it;
			}
		}

		print_container(lt);
	}

	void test_list3()
	{
		list<int> lt1;
		lt1.push_back(1);
		lt1.push_back(2);
		lt1.push_back(3);
		lt1.push_back(4);

		list<int> lt2(lt1);

		print_container(lt1);
		print_container(lt2);

		list<int> lt3;
		lt3.push_back(10);
		lt3.push_back(20);
		lt3.push_back(30);
		lt3.push_back(40);

		lt1 = lt3;
		print_container(lt1);
		print_container(lt3);
	}

	void func(const list<int>& lt)
	{
		print_container(lt);
	}

	void test_list4()
	{
		// 直接构造
		list<int> lt0({ 1,2,3,4,5,6 });
		// 隐式类型转换
		list<int> lt1 = { 1,2,3,4,5,6,7,8 };
		const list<int>& lt3 = { 1,2,3,4,5,6,7,8 };

		func(lt0);
		func({ 1,2,3,4,5,6 });

		print_container(lt1);

		/*auto il = { 10, 20, 30 };
	    initializer_list<int> il = { 10, 20, 30 };
		cout << typeid(il).name() << endl;
		cout << sizeof(il) << endl;*/
	}
	void test_list5()
	{
		list<int> lt1;
		lt1.push_back(1);
		lt1.push_back(2);
		lt1.push_back(3); 
		lt1.push_back(4);
		print_container(lt1);

		auto it = lt1.rbegin();
		while (it != lt1.rend())
		{
			*it += 10;
			cout << *it << " ";
			++it;
		}
		cout << endl;
	
	}
}

test.cpp

cpp 复制代码

#include"List.h"

int main()
{
	sy::test_list4();
	return 0;
}