使用 gettimeofday 和 localtime 获得准确的时间戳
我正在尝试通过 gettimeoday 和 localtime 监视多个应用程序和数据路径上经过的系统时间。在此示例中，我想在代码运行之前获取系统时间（微秒精度）。我目前正在这样做：
#include <stdio.h>
#include <sys/time.h>
struct timeval tv;
struct timezone tz;
struct tm *tm;
**code I don't care about**
gettimeofday(&tv, NULL);
tm=localtime(&tv.tv_sec);
**code to watch**
printf(" %d:%02d:%02d %ld \n", tm->tm_hour, tm->tm_min,
tm->tm_sec, tv.tv_usec);
据我了解，本地时间调用肯定会产生一些开销，并且可能会降低准确性。我可能完全错了，但是我应该等到我的要观看的代码完成后才调用 localtime 吗？我假设 localtime 只是对 gettimeofday 的结果进行半昂贵的转换，因此它应该放在 printf 语句之前。
I'm attempting to monitor system time elapsed across multiple applications and data paths via gettimeoday and localtime. In this example, I want to grab the system time (microsecond percision) right before my code runs. I'm currently doing it like this:
#include <stdio.h>
#include <sys/time.h>
struct timeval tv;
struct timezone tz;
struct tm *tm;
**code I don't care about**
gettimeofday(&tv, NULL);
tm=localtime(&tv.tv_sec);
**code to watch**
printf(" %d:%02d:%02d %ld \n", tm->tm_hour, tm->tm_min,
tm->tm_sec, tv.tv_usec);
From what I understand the localtime call definitely incurs a bit of overhead and can throw off accuracy. I might be totally wrong on this, but should I wait to call localtime until after my code to watch completes? I'm assuming that localtime is just doing a semi-expensive conversion of gettimeofday's results, and thus it should be placed right before the printf statement.
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如果您确实需要微秒精度，是的。如果
localtime在不到一微秒的时间内执行，我会感到非常惊讶。但如果 gettimeofday 具有微秒分辨率，我也会感到惊讶，即使实际计时器具有微秒分辨率（极不可能），从系统返回时的上下文切换可能会花费超过一微秒（并且可能比调用localtime更长）。事实是，除非直接访问特殊硬件，否则您无法获得接近微秒的分辨率。If you really need microsecond accuracy, yes. I'd be very surprised if
localtimeexecuted in less than a microsecond. But I'd also be surprised ifgettimeofdayhad a microsecond resolution, and even if the actual timer did (highly unlikely), the context switch when returning from the system will probably take well over a microsecond (and could be longer than the call tolocaltime). The fact is that except when accessing special hardware directly, you can't get anywhere near microsecond resolution.