linux 下的gettimeofday 函数在windows上的替换方案

方案一：

#include
#ifdef WIN32
# include
#else
# include
#endif
#ifdef WIN32
int
gettimeofday(struct timeval *tp, void *tzp)
{
time_t clock;
struct tm tm;
SYSTEMTIME wtm;
GetLocalTime(&wtm);
tm.tm_year = wtm.wYear - 1900;
tm.tm_mon = wtm.wMonth - 1;
tm.tm_mday = wtm.wDay;
tm.tm_hour = wtm.wHour;
tm.tm_min = wtm.wMinute;
tm.tm_sec = wtm.wSecond;
tm. tm_isdst = -1;
clock = mktime(&tm);
tp->tv_sec = clock;
tp->tv_usec = wtm.wMilliseconds * 1000;
return (0);
}
#endif

方案二：

gettimeofday的使用

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//copy from muduo
Timestamp Timestamp::now()
{
struct timeval tv;
gettimeofday(&tv, NULL);//返回1970年至今的秒+微秒
int64_t seconds = tv.tv_sec;
return Timestamp(seconds * kMicroSecondsPerSecond + tv.tv_usec);
}

gettimeofday要求传入一个timeval和一个时区。因为存在微秒数，显然它比 time_t now = ::time(NULL)更精确。

但是这个函数是linux下的。所以我们需要一个跨平台的实现。

以下是一个实现，使用c++的chrono库。

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#include <chrono>
int gettimeofday(struct timeval *__restrict __tv, __timezone_ptr_t __tz)
{
auto now = std::chrono::system_clock::now();
auto now_ticks = std::chrono::duration_cast<std::chrono::microseconds>(now.time_since_epoch());//
__tv->tv_sec = (long)now_ticks.count() / 1000000;
__tv->tv_usec = (long)now_ticks.count() % 1000000;
return 0;
}

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now.time_since_epoch()返回的duration比较奇怪,需要转化成微秒。

其实主要是windows没有这个函数，那么我们实现它。

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//copy from evpp
#ifdef WIN32
int gettimeofday(struct timeval* tp, void* tzp) {
uint64_t intervals;
FILETIME ft;

GetSystemTimeAsFileTime(&ft);

/*
* A file time is a 64-bit value that represents the number
* of 100-nanosecond intervals that have elapsed since
* January 1, 1601 12:00 A.M. UTC.
*
* Between January 1, 1970 (Epoch) and January 1, 1601 there were
* 134744 days,
* 11644473600 seconds or
* 11644473600,000,000,0 100-nanosecond intervals.
*
* See also MSKB Q167296.
*/

intervals = ((uint64_t)ft.dwHighDateTime << 32) | ft.dwLowDateTime;
intervals -= 116444736000000000;

tp->tv_sec = (long)(intervals / 10,000,000);
tp->tv_usec = (long)((intervals % 10000000) / 10);

return (0);
}