如何在 Linux 中从 C 打印毫秒和纳秒精度的时间差异？
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How to print time difference in accuracy of milliseconds and nanoseconds from C in Linux?
提问by kingsmasher1
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.
我有这个程序可以打印 2 个不同实例之间的时间差，但它以秒的精度打印。我想以毫秒为单位打印它，另一个以纳秒为单位打印。
//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?
我怎样才能做到这一点？
采纳答案by Basile Starynkevitch
Read first the time(7)man page.
首先阅读time(7)手册页。
Then, you can use clock_gettime(2)syscall (you may need to link -lrtto get it).
然后，您可以使用clock_gettime(2)系统调用（您可能需要链接-lrt以获取它）。
So you could try
所以你可以试试
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));
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_getresto query the resolution of some clock.
不要期望硬件计时器具有纳秒精度，即使它们提供纳秒分辨率。并且不要尝试测量小于几毫秒的持续时间：硬件不够忠实。您可能还想用于clock_getres查询某个时钟的分辨率。
