blocks|key|2613211|text|首先阅读time(7)手册页。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2613212|然后，您可以使用gettime(2)+syscall+(您可能需要链接-lrt来获得它)。|style|CODE|2613213|所以你可以试试|2613214|++++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+%25.5f+seconds\n",
+++++++++++((double)tend.tv_sec+%2B+1.0e-9*tend.tv_nsec)+-+
+++++++++++((double)tstart.tv_sec+%2B+1.0e-9*tstart.tv_nsec));|code-block|syntax|javascript|2613215|不要期望硬件计时器具有纳秒精度，即使它们能提供纳秒分辨率。不要尝试测量时间持续时间小于几毫秒:硬件不够可靠。您还可能希望使用clock_getres查询某些时钟的分辨率。|2613216|entityMap|0|LINK|mutability|MUTABLE|url|http://man7.org/linux/man-pages/man7/time.7.html|1|http://man7.org/linux/man-pages/man2/clock_gettime.2.html^0|4|7|0|0|Z|4|8|A|1|0|0|0|1Q|C|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@$A|15|B|16|F|G]]|9|@$A|17|B|18|1|19]]|C|$]]|$1|H|3|I|5|6|7|1A|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|1B|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1C|8|@$A|1D|B|1E|F|G]]|9|@]|C|$]]|$1|Q|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]]]

Read first the <a href="http://man7.org/linux/man-pages/man7/time.7.html">time(7)</a> man page.

Then, you can use <a href="http://man7.org/linux/man-pages/man2/clock_gettime.2.html">clock_gettime(2)</a> syscall (you may need to link <code>-lrt</code> to get it).

So you could try

<pre><code> struct timespec tstart={0,0}, tend={0,0};
 clock_gettime(CLOCK_MONOTONIC, &amp;tstart);
 some_long_computation();
 clock_gettime(CLOCK_MONOTONIC, &amp;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));
</code></pre>

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 <code>clock_getres</code> to query the resolution of some clock.

blocks|key|2812188|text|timespec_get+来自C11|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|2812189|此函数返回纳秒，四舍五入到实现的分辨率。|2812190|示例来自：get：|2812191|#include+<stdio.h>
#include+<time.h>

int+main(void)
{
++++struct+timespec+ts;
++++timespec_get(&ts,+TIME_UTC);
++++char+buff[100];
++++strftime(buff,+sizeof+buff,+"%25D+%25T",+gmtime(&ts.tv_sec));
++++printf("Current+time:+%25s.%2509ld+UTC\n",+buff,+ts.tv_nsec);
}|code-block|syntax|javascript|2812192|输出：|2812193|Current+time:+02/18/15+14:34:03.048508855+UTC|2812194|这里有更多详细信息：https://stackoverflow.com/a/36095407/895245|2812195|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/c/chrono/timespec_get|1|https://stackoverflow.com/a/36095407/895245^0|0|C|D|5|0|C|0|0|5|3|0|0|0|0|0|A|17|1|0^^$0|@$1|2|3|4|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|1C|8|@]|E|@]|F|$]]|$1|I|3|J|5|6|7|1D|8|@]|E|@$9|1E|A|1F|1|1G]]|F|$]]|$1|K|3|L|5|M|7|1H|8|@]|E|@]|F|$N|O]]|$1|P|3|Q|5|6|7|1I|8|@]|E|@]|F|$]]|$1|R|3|S|5|M|7|1J|8|@]|E|@]|F|$N|O]]|$1|T|3|U|5|6|7|1K|8|@]|E|@$9|1L|A|1M|1|1N]]|F|$]]|$1|V|3|-4|5|6|7|1O|8|@]|E|@]|F|$]]]|W|$X|$5|Y|Z|10|F|$11|12]]|13|$5|Y|Z|10|F|$11|14]]]]

<code>timespec_get</code> from C11

This function returns up to nanoseconds, rounded to the resolution of the implementation.

Example from: <a href="http://en.cppreference.com/w/c/chrono/timespec_get" rel="noreferrer">http://en.cppreference.com/w/c/chrono/timespec_get</a> :

<pre><code>#include &lt;stdio.h&gt;
#include &lt;time.h&gt;

int main(void)
{
 struct timespec ts;
 timespec_get(&amp;ts, TIME_UTC);
 char buff[100];
 strftime(buff, sizeof buff, "%D %T", gmtime(&amp;ts.tv_sec));
 printf("Current time: %s.%09ld UTC\n", buff, ts.tv_nsec);
}
</code></pre>

Output:

<pre><code>Current time: 02/18/15 14:34:03.048508855 UTC
</code></pre>

More details here: <a href="https://stackoverflow.com/a/36095407/895245">https://stackoverflow.com/a/36095407/895245</a>

blocks|key|1774460|text|下面是一个处理它的简单宏|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1774461|#include+<time.h>
#define+CHECK_TIME(x)+{\
++++struct+timespec+start,end;\
++++clock_gettime(CLOCK_REALTIME,+&start);\
++++x;\
++++clock_gettime(CLOCK_REALTIME,+&end);\
++++double+f+=+((double)end.tv_sec*1e9+%2B+end.tv_nsec)+-+((double)start.tv_sec*1e9+%2B+start.tv_nsec);+\
++++printf("time+%25f+ms\n",f/1000000);+\
++++}|code-block|syntax|javascript|1774462|下面是如何使用它：|1774463|CHECK_TIME(foo(a,b,c))|1774464|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

here is a simple macro to deal with it
<pre class="lang-c prettyprint-override"><code>#include &lt;time.h&gt;
#define CHECK_TIME(x) {\
 struct timespec start,end;\
 clock_gettime(CLOCK_REALTIME, &amp;start);\
 x;\
 clock_gettime(CLOCK_REALTIME, &amp;end);\
 double f = ((double)end.tv_sec*1e9 + end.tv_nsec) - ((double)start.tv_sec*1e9 + start.tv_nsec); \
 printf(&quot;time %f ms\n&quot;,f/1000000); \
 }
</code></pre>
and here is how to use it:
<pre class="lang-c prettyprint-override"><code>CHECK_TIME(foo(a,b,c))
</code></pre>

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.

<pre><code>//Prints in accuracy of seconds

#include &lt;stdio.h&gt;
#include &lt;time.h&gt;

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

 time(&amp;now);
 sleep(2);

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

 printf("%.f seconds difference", seconds);
}
</code></pre>

How can I accomplish that?

How to print time difference in accuracy of milliseconds and nanoseconds from C in Linux?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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问如何在Linux中从C打印毫秒和纳秒的时间差？EN