how to use gettimeofday() or something equivalent

问题:

Could someone please help me to use gettimeofday() function with Visual Studio C++ 2008 on Windows XP? here is a code that I found somewhere on the net:

#include < time.h >
#include <windows.h> 

#if defined(_MSC_VER) || defined(_MSC_EXTENSIONS)
  #define DELTA_EPOCH_IN_MICROSECS  11644473600000000Ui64
#else
  #define DELTA_EPOCH_IN_MICROSECS  11644473600000000ULL
#endif

struct timezone 
{
  int  tz_minuteswest; /* minutes W of Greenwich */
  int  tz_dsttime;     /* type of dst correction */
};

int gettimeofday(struct timeval *tv, struct timezone *tz)
{
  FILETIME ft;
  unsigned __int64 tmpres = 0;
  static int tzflag;

  if (NULL != tv)
  {
    GetSystemTimeAsFileTime(&ft);

    tmpres |= ft.dwHighDateTime;
    tmpres <<= 32;
    tmpres |= ft.dwLowDateTime;

    /*converting file time to unix epoch*/
    tmpres -= DELTA_EPOCH_IN_MICROSECS; 
    tmpres /= 10;  /*convert into microseconds*/
    tv->tv_sec = (long)(tmpres / 1000000UL);
    tv->tv_usec = (long)(tmpres % 1000000UL);
  }

  if (NULL != tz)
  {
    if (!tzflag)
    {
      _tzset();
      tzflag++;
    }
    tz->tz_minuteswest = _timezone / 60;
    tz->tz_dsttime = _daylight;
  }

  return 0;
}

...
// call gettimeofday()
 gettimeofday(&tv, &tz); 
 tm = localtime(&tv.tv_sec); 

Last year when I tested this code with VC++6, it worked fine. But now as I use VC++ 2008, I am getting error of exception handling. So is there any idea on how to use gettimeofday or something equivalent?

Thanks for your reply and any help would be very appreciated:

回答1:

In UNIX the use of the timezone struct is obsolete. I don't know why you use it. See http://linux.about.com/od/commands/l/blcmdl2_gettime.htm But if you want to use this structure to know about GMT(UTC) diffrence from your local time it will be next: tz_minuteswest is the real diffrence in minutes from GMT(UTC) and a tz_dsttime is a flag indicates whether daylight is now in use.

Your example with some changes works fine in Visual C++ 2008 Express:

#include "stdafx.h"
#include <time.h>
#include <windows.h> 

const __int64 DELTA_EPOCH_IN_MICROSECS= 11644473600000000;

/* IN UNIX the use of the timezone struct is obsolete;
 I don't know why you use it. See http://linux.about.com/od/commands/l/blcmdl2_gettime.htm
 But if you want to use this structure to know about GMT(UTC) diffrence from your local time
 it will be next: tz_minuteswest is the real diffrence in minutes from GMT(UTC) and a tz_dsttime is a flag
 indicates whether daylight is now in use
*/
struct timezone2 
{
  __int32  tz_minuteswest; /* minutes W of Greenwich */
  bool  tz_dsttime;     /* type of dst correction */
};

struct timeval2 {
__int32    tv_sec;         /* seconds */
__int32    tv_usec;        /* microseconds */
};

int gettimeofday(struct timeval2 *tv/*in*/, struct timezone2 *tz/*in*/)
{
  FILETIME ft;
  __int64 tmpres = 0;
  TIME_ZONE_INFORMATION tz_winapi;
  int rez=0;

   ZeroMemory(&ft,sizeof(ft));
   ZeroMemory(&tz_winapi,sizeof(tz_winapi));

    GetSystemTimeAsFileTime(&ft);

    tmpres = ft.dwHighDateTime;
    tmpres <<= 32;
    tmpres |= ft.dwLowDateTime;

    /*converting file time to unix epoch*/
    tmpres /= 10;  /*convert into microseconds*/
    tmpres -= DELTA_EPOCH_IN_MICROSECS; 
    tv->tv_sec = (__int32)(tmpres*0.000001);
    tv->tv_usec =(tmpres%1000000);


    //_tzset(),don't work properly, so we use GetTimeZoneInformation
    rez=GetTimeZoneInformation(&tz_winapi);
    tz->tz_dsttime=(rez==2)?true:false;
    tz->tz_minuteswest = tz_winapi.Bias + ((rez==2)?tz_winapi.DaylightBias:0);

  return 0;
}


int _tmain(int argc, _TCHAR* argv[])
{
struct timeval2 tv;
struct timezone2 tz;
struct tm *tm1; 
time_t time1;

ZeroMemory(&tv,sizeof(tv));
ZeroMemory(&tz,sizeof(tz));

gettimeofday(&tv, &tz); // call gettimeofday()
time1=tv.tv_sec;
tm1 = localtime(&time1); 



 FILE *f;
 f=fopen("rez.txt","w");

 fprintf(f,"%04d.%02d.%02d %02d:%02d:%02d\n",1900+tm1->tm_year,1+tm1->tm_mon,tm1->tm_mday,tm1->tm_hour,tm1->tm_min,tm1->tm_sec);
 fprintf(f,"Diffrence between GMT(UTC) and local time=%d %s\n",tz.tz_minuteswest,"minutes");
 fprintf(f,"Is Daylight now=%s\n",tz.tz_dsttime?"Yes":"No");

 fclose(f);
 return 0;
}

回答2:

Simple stopwatch in seconds

FWIW: This is a similar one as that of Kate, but I just wanted to mention it, if someone is looking for the most simple stopwatch in C++ (counting seconds). Not a big deal, I know. It has only resolution of 1 sec, so if you want to cound microsecs, go on with the other examples.

double seconds=0;
time_t timer1, timer2;
time(&timer1);  /* get current time  */
...
time(&timer2);  /* get current time  later */
seconds = difftime(timer2,timer1);

回答3:

There are a few different types to represent a time. Here's some code I used recently:

time_t now;
tm* local;
time(&now); 
local=localtime(&now);

I then went on to build a string from pieces of local, but you could do what you wanted at this point.

Kate