如何打印毫秒和纳秒的精度的时差？ [英] How to print time difference in accuracy of milliseconds and nanoseconds?

问题描述

我有这个程序，打印2个不同的实例之间的时间差，但它在几秒钟准确性打印。我想打印在纳秒差异毫秒另一个。

I have this program which prints the time difference between 2 different instances, but it prints in accuracy of seconds. I want to print it in milliseconds and another in nanoseconds difference.

//Prints in accuracy of seconds

#include <stdio.h>
#include <time.h>

int main(void)
{
    time_t now, later;
    double seconds;

    time(&now);
    sleep(2);

    time(&later);
    seconds = difftime(later, now);

    printf("%.f seconds difference", seconds);
}

我怎样才能做到呢？

How can I accomplish that?

推荐答案

首先阅读时间（ 7）手册页。

然后，您可以使用 clock_gettime（2）系统调用（您可能需要链接 -lrt 来得到它）。

Then, you can use clock_gettime(2) syscall (you may need to link -lrt to get it).

所以，你可以尝试

    struct timespec tstart={0,0}, tend={0,0};
    clock_gettime(CLOCK_MONOTONIC, &tstart);
    some_long_computation();
    clock_gettime(CLOCK_MONOTONIC, &tend);
    printf("some_long_computation took about %.5f seconds\n",
           ((double)tend.tv_sec + 1.0e-9*tend.tv_nsec) - 
           ((double)tstart.tv_sec + 1.0e-9*tstart.tv_nsec));

不要指望硬件定时器有一个精确到纳秒，即使他们给纳秒的分辨率。不要试图测量持续时间小于几毫秒：硬件是不是忠实不够。您也可以使用 clock_getres 来查询一些时钟的分辨率。

Don't expect the hardware timers to have a nanosecond accuracy, even if they give a nanosecond resolution. And don't try to measure time durations less than several milliseconds: the hardware is not faithful enough. You may also want to use clock_getres to query the resolution of some clock.

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