c++的时间点time_point基本用法

参考链接：

https://en.cppreference.com/w/cpp/chrono/time_point

time_point是c++标准库里的，不需要引入第三方库

使用时需要添加头文件

#include <chrono>

#include <iomanip>

time_point其实是一个模板类，工作时需要clock的帮助，可以是system_clock、monotonic_clock、high_resolution_clock

这里使用system_clock

下面的代码简单写了一下使用方法，比较水直接看代码吧

#include "pch.h"
#include <string>
#include <sstream>
#include <iostream>
#include <chrono>
#include <iomanip>


int main()
{
    // get current time
    std::chrono::time_point<std::chrono::system_clock> nowTime = std::chrono::system_clock::now();
    std::time_t tmNowTime = std::chrono::system_clock::to_time_t(nowTime);
    std::cout << "nowTime\t" << std::put_time(std::localtime(&tmNowTime), "%F %T") << std::endl;

    // default_value
    std::chrono::time_point<std::chrono::system_clock> startTime;// 1970-1-1 8:0:0;
    std::time_t tmStartTime = std::chrono::system_clock::to_time_t(startTime);
    std::cout << "startTime\t" << std::put_time(std::localtime(&tmStartTime), "%F %T") << std::endl;

    // use timestamp
    // 2020-01-08 15:05:50(1578466970)
    std::chrono::time_point<std::chrono::system_clock> stampTime(std::chrono::seconds(1578466970));
    std::time_t tmStampTime = std::chrono::system_clock::to_time_t(stampTime);
    std::cout << "stampTime\t" << std::put_time(std::localtime(&tmStampTime), "%F %T") << std::endl;

    // some hours ago
    std::time_t tmSomeTimeAgo = std::chrono::system_clock::to_time_t(nowTime - std::chrono::hours(22) - std::chrono::minutes(30));
    std::cout << "22 hours 30 minutes ago\t" << std::put_time(std::localtime(&tmSomeTimeAgo), "%F %T") << std::endl;

    // get time from string
    // use "std::get_time()"
    std::tm aTime;
    std::string strTime("2008-08-08 10:0:0");
    std::stringstream ssTime(strTime);
    ssTime.imbue(std::locale("de_DE.utf-8"));
    ssTime >> std::get_time(&aTime, "%Y-%m-%d %H:%M:%S");
    std::chrono::time_point<std::chrono::system_clock> tp = std::chrono::system_clock::from_time_t(std::mktime(&aTime));
    std::time_t aTestTime = std::chrono::system_clock::to_time_t(tp);
    std::cout << "aTime\t" << std::put_time(std::localtime(&aTestTime), "%F %T") << std::endl;

    std::cout << "compare: nowTime >= aTime ?\t" << (nowTime >= tp ? "true" : "false") << std::endl;

    // end time
    std::chrono::time_point<std::chrono::system_clock> endTime = std::chrono::system_clock::now();
    std::time_t tmEndTime = std::chrono::system_clock::to_time_t(endTime);
    std::cout << "endTime\t" << std::put_time(std::localtime(&tmEndTime), "%F %T") << std::endl;
    std::cout << "the program used\t" << std::chrono::duration_cast<std::chrono::microseconds>(endTime - nowTime).count() << "us.\n";
}

从字符串获得time_point的时候借助了stringstream，并且需要知道字符串的对应格式，使用std::get_time函数将字符串转换成std::time_t，再转换成time_pointt

比较时间前后关系也很方便，直接使用>、<、>=、<=、!=、==这种比较运算符就可以

输出结果：