C++STL中，map和unordered_map插入数据效率对比

概述

对于一般印象而言，有序的map容器比无序的unordered_map容器的插入效率要低一点，本次测试比较两种容器使用insert、emplace、操作符[]插入数据的效率。

运行环境

VS 2017，解决方案配置为release。

测试代码

#include <iostream>
#include <time.h>
#include <map>
#include <unordered_map>
using namespace std;

const int kRunTime1 = 1000 * 1000;     // 循环次数
const int kRunTime2 = 1000 * 10000;
int main()
{
	map<int, int> mp;
	unordered_map<int, int> unordermp;

	time_t st, et;

	cout << "插入个数 = " << kRunTime1 << endl;
	st = clock();
	for (int i = 0; i < kRunTime1; ++i)
	{
		mp.insert(make_pair(i, i));
	}
	et = clock();
	cout << "1 有序map测试时间insert time:" << double(et - st) << "ms" << endl;

	mp.clear();
	st = clock();
	for (int i = 0; i < kRunTime1; ++i)
	{
		mp[i] = i;
	}
	et = clock();
	cout << "1 有序map测试时间操作符[] time:" << double(et - st) << "ms" << endl;

	st = clock();
	for (int i = 0; i < kRunTime1; ++i)
	{
		unordermp.insert(make_pair(i, i));
	}
	et = clock();
	cout << "1 无序map测试时间insert time:" << double(et - st) << "ms" << endl;

	unordermp.clear();
	st = clock();
	for (int i = 0; i < kRunTime1; ++i)
	{
		unordermp[i] = i;
	}
	et = clock();
	cout << "1 无序map测试时间操作符[] time:" << double(et - st) << "ms" << endl;

	cout << "\n插入个数 = " << kRunTime2 << endl;
	mp.clear();
	st = clock();
	for (int i = 0; i < kRunTime2; ++i)
	{
		mp.insert(make_pair(i, i));
	}
	et = clock();
	cout << "2 有序map测试时间insert  time:" << double(et - st) << "ms" << endl;

	mp.clear();
	st = clock();
	for (int i = 0; i < kRunTime2; ++i)
	{
		mp.emplace(make_pair(i, i));
	}
	et = clock();
	cout << "2 有序map测试时间emplace time:" << double(et - st) << "ms" << endl;

	mp.clear();
	st = clock();
	for (int i = 0; i < kRunTime2; ++i)
	{
		mp[i] = i;
	}
	et = clock();
	cout << "2 有序map测试时间操作符[] time:" << double(et - st) << "ms" << endl;

	unordermp.clear();
	st = clock();
	for (int i = 0; i < kRunTime2; ++i)
	{
		unordermp.insert(make_pair(i, i));
	}
	et = clock();
	cout << "2 无序map测试时间insert  time:" << double(et - st) << "ms" << endl;

	unordermp.clear();
	st = clock();
	for (int i = 0; i < kRunTime2; ++i)
	{
		unordermp.emplace(make_pair(i, i));
	}
	et = clock();
	cout << "2 无序map测试时间emplace time:" << double(et - st) << "ms" << endl;

	unordermp.clear();
	st = clock();
	for (int i = 0; i < kRunTime2; ++i)
	{
		unordermp[i] = i;
	}
	et = clock();
	cout << "2 无序map测试时间操作符[] time:" << double(et - st) << "ms" << endl;

	system("pause");
	return 0;
}

运行结果

测试结果

结果显示，无序容器unordered_map的插入效率普遍低于有序容器map，与参考博文中结果相反。请问是否有人能够指点一二，解释这种现象的原因。

参考网址

程序改写自
链接：https://blog.youkuaiyun.com/muyuyuzhong/article/details/82712147
感谢博主流媒体程序员的创作。