// A stack version of SysAllocString
#define DECL_STACK_BSTR(name, wideString) \
    BSTR name = NULL; \
    { \
        UINT bytesReq = sizeof(wideString) + sizeof(UINT); \
        UINT* temp = static_cast<UINT*>(_alloca(bytesReq)); \
        *temp = bytesReq - sizeof(UINT); \
        ++temp; \
        wmemcpy((WCHAR*)temp, wideString, ARRAYSIZE(wideString)); \
        name = (BSTR)temp; \
    }

#define DECL_STACK_BSTR_SIZE(name, size) \
    BSTR name = NULL; \
    { \
        UINT bytesReq = size + sizeof(UINT); \
        UINT* temp = static_cast<UINT*>(_alloca(bytesReq)); \
        *temp = bytesReq - sizeof(UINT); \
        ++temp; \
        name = (BSTR)temp; \
    }

DECL_STACK_BSTR_SIZE(taskTime, sizeof("YYYY-MM-DDTHH:MM:SS+HH:MM"));

// wmiStr is a date from WMI, such as Win32_OperatingSystem::LocalDateTime
// task time needs to be from
// DECL_STACK_BSTR_SIZE(taskTime, sizeof("YYYY-MM-DDTHH:MM:SS+HH:MM"));
// or 
// SysAllocStringLen(NULL, sizeof("YYYY-MM-DDTHH:MM:SS+HH:MM"))
// or any other bstr with at least 26 WCHARs / 52 bytes in size
void WMITimeToTaskTime(BSTR wmiStr, BSTR taskTime)
{
	// from YYYYMMDDHHMMSS.XXXXXX(+-)OOO
	// to   YYYY-MM-DDTHH:MM:SS(+-)HH:MM
	WCHAR* startOfString = wmiStr;
	WCHAR* endOfString = startOfString + (sizeof("YYYYMMDDHHMMSS.MMMMMM+OOO") - 1);
	WCHAR* endOfMinutes = endOfString - 4;
	assert((*endOfMinutes) == L'+' || ((*endOfMinutes) == L'-'));
	// figure out the number of minutes used for time zone adjustment
	UINT minutes = 0;
	for(WCHAR* pEnd = endOfString - 1; pEnd != endOfMinutes; --pEnd)
	{
		minutes *= 10;
		minutes += (*pEnd - L'0');
	}
	// turn it into hours and minutes
	UINT hours = minutes / 60;
	minutes %= 60;
	// build the hh:mm picture
	WCHAR timeInFormat[7];
	timeInFormat[0] = *endOfMinutes;
	timeInFormat[3] = L':';
	for(int i = 2; i >= 1; --i)
	{
		timeInFormat[i] = ((hours % 10) + L'0');
		timeInFormat[i + 3] = ((minutes % 10) + L'0');
		hours /= 10;
		minutes /= 10;
	}
	timeInFormat[6] = 0;
	WCHAR* years = taskTime;
	const int yearLen = 4;
	WCHAR* month = years + yearLen + 1;
	const int otherLen = 2;
	*(years + yearLen) = *(month + otherLen) = L'-';
	WCHAR* days = month + otherLen + 1;
	*(days + otherLen) = L'T';
	WCHAR* hoursStr = days + otherLen + 1;
	WCHAR* minutesStr = hoursStr + otherLen + 1;
	WCHAR* seconds = minutesStr + otherLen + 1;
	*(hoursStr + otherLen) = *(minutesStr + otherLen) = L':';
	__movsw((USHORT*)seconds + otherLen, (USHORT*)timeInFormat, 7);
	WCHAR* wmiTimeStr = wmiStr;
	// copy years
	ULONGLONG* srcLL = (ULONGLONG*)wmiTimeStr, *dstLL = (ULONGLONG*)years;
	*dstLL = *srcLL;
	wmiTimeStr += yearLen;
	// copy months
	ULONG* srcUL = (ULONG*)wmiTimeStr, *dstUL = (ULONG*)month;
	*dstUL = *srcUL;
	++srcUL;
	// copy days
	dstUL = (ULONG*)days;
	*dstUL = *srcUL;
	++srcUL;
	// copy hours
	dstUL = (ULONG*)hoursStr;
	*dstUL = *srcUL;
	++srcUL;
	// copy minutes
	dstUL = (ULONG*)minutesStr;
	*dstUL = *srcUL;
	++srcUL;
	// copy seconds
	dstUL = (ULONG*)seconds;
	*dstUL = *srcUL;
}