C++---实用编程技巧记录（使用库函数/ lambda表达式求最小、大值，排序等）

注：为了写出高质量的代码，一些简单的逻辑尽量用库函数去实现，减少代码量；

1. 求最小值/最大值

• 普通vector 求最小值

std::vector<double>  x={0,2,3,7,4,1};
auto min_inter = std::min_element(x.begin(), x.end());
double min= *min_inter; // 值
int index = std::distance(x.begin(),min_inter); //索引

• map或者vector 根据需要根据某一维度数值获得最大最小值

// 使用lambda表达式
std::vector<cv::Point2f> pts;
auto compare_x = [](const cv::Point2f &p0, const cv::Point2f &p1) -> bool {
    return (p0.x < p1.x);
};
auto min_inter = std::min_element(pts.begin(), pts.end(),compare_x);
cv::Point2f min= *min_inter; // 值
int index = std::distance(pts.begin(),min_inter); //索引

以上当然可以直接进行排序，使用 sort函数

2. 排序

std::vector<cv::Point2f> pts;
// 升序
auto sort_x = [](const cv::Point2f &p0, const cv::Point2f &p1) -> bool {
    return (p0.x < p1.x);
};
std::sort(pts.begin(), pts.end(), sort_x);

lambda表达式 简写版：

std::sort(pts.begin(), pts.end(), [](const cv::Point2f &p0, const cv::Point2f &p1) {return p0.x < p1.x;});

3. 均值

double mean_ms = std::accumulate(std::begin(all_times),
                                           std::end(all_times), 0.0) /
                           all_times.size();

4 lambda 与多线程

4.1 多线程（类函数）

买东西 ：

class MyClassTest() {
   
   
    bool Buy(std::string type, int money) {
   
   
        // do something
        for (int i = 0; i < 10; ++i) {
   
   
            std::cout << "now is buy : " << type << std::endl;
        }
        return true;
    }
    bool RunMultiBuy() {
   
   
        auto buy_thread_0 =
            std::make_shared<std::thread>(&MyClassTest::Buy, this, "book", 20);
        buy_thread_0->join();

        auto buy_thread_1 =
            std::make_shared<std::thread>(&MyClassTest::Buy, this, "pen", 10);
        buy_thread_1->join();
    }
}

4.2 多线程（使用lambda）

买东西 ：

class MyClassTest() {
   
   
    bool RunMultiBuy() {
   
   
    	// lambda 已获取 this
        auto buy = [this](std::string type, int money) {
   
   
            // do something
            for (int i = 0; i < 10; ++i) {
   
   
                std::cout << "now is buy : " << type << std::endl;
            }
            return true;
        };

        auto buy_thread_0 = std::make_shared<std::thread>(buy, "book", 20);
        buy_thread_0->join();

        auto buy_thread_1 = std::make_shared<std::thread>(buy, "pen", 10);
        buy_thread_1->join();
    }
}

5. 查找

map 根据value 查找 key

 const std::map<std::string, int> str_id_map = {
   
   
    {
   
   "jack", 23424}, {
   
   "tom", 12533}, {
   
   "hopo", 5496}};
    
 int id = 12533;
 std::string name = "";
 const auto& str_map = str_id_map;
 auto iter =
     std::find_if(str_map.begin(), str_map.end(),
                  [id](const auto& item) {
   
    return item.second == id; });

 if (iter != str_map.end()) {
   
   
     name = iter->first;
 }

        

6. 对数组根据某个值进行分段

1. 包含对数据的打印
2. 对分段使用库函数处理

#include <algorithm>
#include <iostream>
#include <vector>

template <typename T>
std::ostream &operator<<(std::ostream &out, const std::vector<T> &ve) {
   
   
    out << "[";
    std::string delimiter = "\0";
    for (auto &item : ve) {
   
   
        out << delimiter << item;
        delimiter = ",";
    }
    out << "]\n";
    return out;
}
int main() {
   
   
    std::vector<int> points{
   
   1, 2, 3, 6};
    int cut_x = 6;
    auto iter =
        std::find_if(points.begin(), points.end(),
                     [&cut_x](const auto &val) {
   
    return val >= cut_x; });

    std::vector<int> points_1, points_2;
    if (iter == points.begin()) {
   
   
        points_2 = points;
    } else if (iter == points.end() || std::next(