HOWTO: Convert a DBTIMESTAMP into a DATE

• Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.2, 5.0, 6.0

SUMMARY

When given a DBTIMESTAMP value, you might need to convert the value into a type that is compatible with COM IDispatch interfaces such as the DATE type. If you are using Microsoft Foundation Classes (MFC), you can use the COleDateTime class to help convert from a DBTIMESTAMP to a DATE. If you are not using MFC, you can still use the code provided by MFC without needing the entire MFC framework.

MORE INFORMATION

If You Are Using MFC, Use this Code

#include <oledb.h>

void MFCTestConversion()
{
   DBTIMESTAMP dbTimeStamp;

   dbTimeStamp.year = 1900;
   dbTimeStamp.month = 1;
   dbTimeStamp.day = 1;
   dbTimeStamp.hour = 0;
   dbTimeStamp.minute = 0;
   dbTimeStamp.second = 0;

   COleDateTime d(dbTimeStamp.year, dbTimeStamp.month, dbTimeStamp.day,  
            dbTimeStamp.hour, dbTimeStamp.minute, dbTimeStamp.second);

   COleVariant var = d;
   DATE date = var.date;
} 

If You Are Using MFC, Use this Code

//headers needed
#include <windows.h>
#include <oledb.h>

// One-based array of days in year at month start
int MonthDays[13] =
	{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365};

// Modified Helper taken from \MFC\SRC\OLEVAR.CPP, _AfxOleDateFromTm
// This will compile in .c files too
BOOL OleDateFromTm(WORD wYear, WORD wMonth, WORD wDay, 
                   WORD wHour, WORD wMinute, WORD wSecond, DATE *dtDest)
{
   long nDate;
   double dblTime;
   BOOL bLeapYear;
   int nDaysInMonth;

   // Validate year and month (ignore day of week and milliseconds)
   if (wYear > 9999 || wMonth < 1 || wMonth > 12)
      return FALSE;

   //  Check for leap year and set the number of days in the month
   bLeapYear = ((wYear & 3) == 0) && ((wYear % 100) != 0 || (wYear % 400) == 0);

   nDaysInMonth = MonthDays[wMonth] - MonthDays[wMonth-1] +
               ((bLeapYear && wDay == 29 && wMonth == 2) ? 1 : 0);

   // Finish validating the date
   if (wDay < 1 || wDay > nDaysInMonth || wHour > 23 || wMinute > 59 || wSecond > 59)
      return FALSE;

   // Cache the date in days and time in fractional days
   //It is a valid date; make Jan 1, 1AD be 1
   nDate = wYear*365L + wYear/4 - wYear/100 + wYear/400 + MonthDays[wMonth-1] + wDay;

   //  If leap year and it's before March, subtract 1:
   if (wMonth <= 2 && bLeapYear)
      --nDate;

   //  Offset so that 12/30/1899 is 0
   nDate -= 693959L;

   dblTime = (((long)wHour * 3600L) +  // hrs in seconds
              ((long)wMinute * 60L) +  // mins in seconds
              ((long)wSecond)) / 86400L;

   *dtDest = (double) nDate + ((nDate >= 0) ? dblTime : -dblTime);
   return TRUE;
}

void TestConversion()
{
   BOOL bRet;
   DBTIMESTAMP dbTimeStamp;
   DATE d;

   dbTimeStamp.year = 1900;
   dbTimeStamp.month = 1;
   dbTimeStamp.day = 1;
   dbTimeStamp.hour = 0;
   dbTimeStamp.minute = 0;
   dbTimeStamp.second = 0;

   bRet = OleDateFromTm(dbTimeStamp.year, dbTimeStamp.month,  
                        dbTimeStamp.day, dbTimeStamp.hour,  
                        dbTimeStamp.minute, dbTimeStamp.second, &d);
   if (bRet) //succeeded...
   {
      //d should equal 2.00
   }
} 

REFERENCES

COleDateTime in MSDN

Additional query words: COleDateTime DBTIMESTAMP OLEDB Conversion VarDateFromStr

Keywords : kbnokeyword kbAutomation kbMFC kbVC400 kbVC420 kbVC500 kbVC600 kbDSupport kbGrpMFCATL
Version : winnt:4.0,4.2,5.0,6.0
Platform : winnt
Issue type : kbhowto