std::chrono简介

参考资料:
博客园
官方文档

chrono主要包括三个部分.

1. clock

clock主要包括三种 system_clock steady_clock high_resolution_clock

  • system_clock是系统时钟，在系统时间回退的时候，计时的结果会跟着回退。 /li>
  • high_resolution_clock，跟系统时钟一样，有计时回退的问题，更适用于精确的计时。
  • steady_clock是单调时钟，不会随着系统时间的回退而改变

示例代码

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#include  <chrono>
#include  <iostream>
#include  <thread>
using namespace std::chrono;
int main(int argc,char * argv[])
{
    auto begin = system_clock::now();
    auto highBegin = high_resolution_clock::now();
    auto steadyBegin = steady_clock::now();
    std::this_thread::sleep_for(60s);
    auto end = system_clock::now();
    auto highEnd = high_resolution_clock::now();
    auto steadyEnd = steady_clock::now();
    duration <double,std::ratio <1,1>> peridSeconds = end-begin;
    duration <double,std::ratio <1,1>> highSeconds = highEnd-highBegin;
    duration <double,std::ratio <1,1>> steadySeconds = steadyEnd - steadyBegin;
    std::cout << "System_clock Time :" << peridSeconds.count() << " s"<<  std::endl;
    std::cout  <<"High Time :" << highSeconds.count() << " s" << std::endl;
    std::cout << "SteadySeconds Time :"  <<steadySeconds.count() << " s"  <<std::endl;

    duration <double,std::nano> peridMillSeconds = end-begin;
    duration <double,std::nano> highPeridMillSeconds = highEnd - highBegin;
    duration <double,std::nano> steadyMillSeconds = steadyEnd - steadyBegin;
    std::cout << "Time :" << peridMillSeconds.count() << " ns" << std::endl;
    std::cout << "High Time :"<<  highPeridMillSeconds.count() << " ns"  <<std::endl;
    std::cout << "Steady Time :" << steadyMillSeconds.count()  <<" ns" << std::endl;
    return 0;
}

不修改系统时间的运行结果：

修改系统时间的运行结果: img src=“https://www.dennisthink.com/image/2019/01/back_result.png)

2.duration

duration是一个模板，用来表示一段时间，可以使用duration_cast在不同的计时单位之间转换。

示例代码

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#include  <chrono>
#include  <iostream>
using namespace std::chrono;
int main(int argc,char * argv[])
{
    using half_hour_type = duration<int,std::ratio<30*60>>;
    using half_day_type = duration<int,std::ratio<12*60*60>>;
    using half_week_type = duration<int,std::ratio <7*12*60*60>>;

    hours one_hour(1);

    hours day_hours(24);
    hours week_hours(7*24);

    half_hour_type half_hours = duration_cast<half_hour_type>(one_hour);
    half_day_type  half_day_hours = duration_cast<half_day_type>(day_hours);
    half_week_type half_weak_hours = duration_cast<half_week_type>(week_hours);
    half_day_type  half_week_to_half_days = duration_cast<half_day_type>(week_hours);
    std::cout  <<"1 hour have "  << half_hours.count()   <<" half_hours "  <<std::endl;
    std::cout << "1 day  have "  << half_day_hours.count() << " half_days "  <<std::endl;
    std::cout << "1 week  have "  << half_weak_hours.count()  " half_weeks "  <<std::endl;
    std::cout << "1 week  have "  << half_week_to_half_days.count()  " half_days "  <<std::endl;
    return 0;
}

程序输出: