BUG: Time Moves Backwards 24 Hours with GetSystemTimeAsFileTime()

• Microsoft Win32 Application Programming Interface (API), included with:
  • Microsoft Windows versions 95, 98

SYMPTOMS

If GetSystemTimeAsFileTime() is called at the precise split second during which the date changes from one day to the next (12:00:00.000 AM), the API may return a value indicating 12:00 AM for the previous day.

RESOLUTION

If it is necessary for your program to guard against this bug, you should keep track of the previously retrieved time and compare the newly retrieved time to it. This method is demonstrated in the sample code at the end of this article. In the event that time "moves backwards," you can immediately call GetSystemTimeAsFileTime() again to retrieve the correct time.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

Steps to Reproduce Behavior

#include <windows.h>
#include <stdio.h>

typedef union {
    unsigned __int64 ft_scalar;
    FILETIME ft_struct;
} FT;

// Function used to display a FILETIME in a human readable format.
void DisplayFileTime(FILETIME* lpFt) {
    FILETIME ftLocalFileTime;
    SYSTEMTIME stLocalSystemTime;

    FileTimeToLocalFileTime(lpFt, &ftLocalFileTime);
    FileTimeToSystemTime( &ftLocalFileTime, &stLocalSystemTime);

    printf("%d/%d/%d %d:%d:%d\n",
        stLocalSystemTime.wMonth,
        stLocalSystemTime.wDay,
        stLocalSystemTime.wYear,
        stLocalSystemTime.wHour,
        stLocalSystemTime.wMinute,
        stLocalSystemTime.wSecond);
}

void main() {

    SYSTEMTIME st;
    FT ft1, ft2;

    DWORD dwStart;
    int i = 0;

    st.wYear = 1999;
    st.wMonth = 1;
    st.wDayOfWeek = 3;
    st.wDay = 12;
    st.wHour = 23;
    st.wMinute = 59;
    st.wSecond = 59;
    st.wMilliseconds = 0;

    while (TRUE)
    {
        i++;
        printf("Test number %u.\n", i);

        // Set the local time to just before midnight.
        SetLocalTime(&st);

        GetSystemTimeAsFileTime(&ft2.ft_struct);
        dwStart = GetTickCount();

        do
        {
            ft1 = ft2;
            GetSystemTimeAsFileTime(&ft2.ft_struct);

            // Check to see if time moved backwards.
            if (ft2.ft_scalar - ft1.ft_scalar > 100000000i64)
            {
                // If discrepancy greater than 100 seconds...
                printf("Time went backwards!\n");
                printf("Time before: ");
                DisplayFileTime(&ft1.ft_struct);
                printf("Time after: ");
                DisplayFileTime(&ft2.ft_struct);

                // Call the API again to get the correct time.
                GetSystemTimeAsFileTime(&ft2.ft_struct);
                printf("Correct time: ");
                DisplayFileTime(&ft2.ft_struct);
                return;
            }
        } while (GetTickCount() - dwStart < 1050);
    }
} 

Additional query words:

Keywords          : kbDateTime kbKernBase kbWinOS95 kbWinOS98 
Version           : winnt:
Platform          : winnt 
Issue type        : kbbug 

Last Reviewed: April 7, 1999