如何在Linux中从C中以毫秒和纳秒的精度打印时间差？ [英] How to print time difference in accuracy of milliseconds and nanoseconds from C in Linux?

问题描述

我有这个程序打印2个不同实例之间的时间差，但它打印的精确度为几秒。我想打印它以毫秒为单位，另一个以毫微秒为单位打印。

  //打印秒精确度
 
 #include< stdio.h> 
 #include< time.h> 
 
 int main（void）
 {
 time_t now，later; 
双秒; 
 
时间（& now）; 
 sleep（2）; 
 
时间（&以后）; 
秒= difftime（稍后，现在）; 
 
 printf（％。f秒差，秒）; 
} 
  

我该如何做到这一点？

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 才能得到它）。

所以你可以试试

pre $ 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花费了大约.5f秒\\\
，
（（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具有纳秒精度，即使它们提供了纳秒级分辨率。并且不要尝试测量小于几毫秒的时间：硬件不够忠诚。您可能还想使用 clock_getres 查询某个时钟的分辨率。

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);
}

How can I accomplish that?

解决方案

Read first the time(7) man page.

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

So you could try

    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));

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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