【c++】遍历容器，哪一种方法速度最快？

遍历容器，哪一种方法速度最快？"/>

【c++】遍历容器，哪一种方法速度最快？

终于有一个简单的每日一题！写完的时候甚至代码还没有编译结束！刚好借今天的每日一题探究一下一直以来的一些疑惑：容器的遍历。
题目大概是这样的：

我们一眼就看到了容器的遍历！！那么众所周知，容器的遍历最常用的有三种：

1. 基础for，也就是for(int i = 0; i < 10; i++)这种格式
2. c++11 的for
3. algorithm中的for_each

下面蘸着这个题写三种遍历，看看执行时间：

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <time.h>
#include <iomanip>using namespace std;int countSeniors(vector<string> &details)
{int cnt = 0;for_each(details.begin(), details.end(), [&cnt](const string &detail){if (detail[11] > '6' || (detail[11] == '6' && detail[12] != '0')) {cnt++;} });return cnt;
}int countSeniors2(vector<string> &details)
{int cnt = 0;for (const auto &detail : details){if (detail[11] > '6' || (detail[11] == '6' && detail[12] != '0')){cnt++;}}return cnt;
}int countSeniors3(vector<string> &details)
{int cnt = 0;for (int i = 0; i < static_cast<int>(details.size()); i++){if (details[i][11] > '6' || (details[i][11] == '6' && details[i][12] != '0')){cnt++;}}return cnt;
}int main()
{vector<string> details = {"7868190130M7522", "5303914400F9211", "9273338290F4010"};cout << setprecision(10);{clock_t startT, finishT;startT = clock();countSeniors(details);finishT = clock();double duration = static_cast<double>(finishT - startT) / CLOCKS_PER_SEC;cout << "匿名函数： " << duration << endl;}{clock_t startT, finishT;startT = clock();countSeniors2(details);finishT = clock();double duration = static_cast<double>(finishT - startT) / CLOCKS_PER_SEC;cout << "c++11 for: " << duration << endl;}{clock_t startT, finishT;startT = clock();countSeniors3(details);finishT = clock();double duration = static_cast<double>(finishT - startT) / CLOCKS_PER_SEC;cout << "基础for： " << duration << endl;}{clock_t startT, finishT;startT = clock();for (int i = 0; i < 100; i++){countSeniors(details);}finishT = clock();double duration = static_cast<double>(finishT - startT) / CLOCKS_PER_SEC;cout << "100 次：匿名函数： " << duration << endl;}{clock_t startT, finishT;startT = clock();for (int i = 0; i < 100; i++){countSeniors2(details);}finishT = clock();double duration = static_cast<double>(finishT - startT) / CLOCKS_PER_SEC;cout << "100 次：c++11 for： " << duration << endl;}{clock_t startT, finishT;startT = clock();for (int i = 0; i < 100; i++){countSeniors3(details);}finishT = clock();double duration = static_cast<double>(finishT - startT) / CLOCKS_PER_SEC;cout << "100 次：基础for： " << duration << endl;}return 0;
}

运行一遍，得到了这样的输出：

Amazing！可以看到这场比赛，匿名函数输得一塌糊涂，反而是朴实无华的for夺魁！
这到底是为什么呢？

–没写完，代码跑完了，一会儿干完活再写