Does the windows FILETIME structure include leap seconds?

The question shouldn't be if FILETIME includes leap seconds.

It should be:

Do the people, functions, and libraries, who interpret a FILETIME (i.e. FileTimeToSystemTime) include leap seconds when counting the duration?

The simple answer is "no". FileTimeToSystemTime returns seconds as 0..59.

The simpler answer is: "of course not, how could it?".

My Windows 2000 machine doesn't know that there were 2 leap seconds added in the decade since it was released. Any interpretation it makes of a FILETIME is wrong.

Finally, rather than relying on logic, we can determine by direct experimental observation, the answer to the posters question:

var    systemTime: TSystemTime;    fileTime: TFileTime;begin    //Construct a system-time for the 12/31/2008 11:59:59 pm    ZeroMemory(@systemTime, SizeOf(systemTime));    systemtime.wYear := 2008;    systemTime.wMonth := 12;    systemTime.wDay := 31;    systemTime.wHour := 23;    systemtime.wMinute := 59;    systemtime.wSecond := 59;    //Convert it to a file time    SystemTimeToFileTime(systemTime, {var}fileTime);    //There was a leap second 12/31/2008 11:59:60 pm    //Add one second to our filetime to reach the leap second    filetime.dwLowDateTime := fileTime.dwLowDateTime+10000000; //10,000,000 * 100ns = 1s    //Convert the filetime, sitting on a leap second, to a displayable system time    FileTimeToSystemTime(fileTime, {var}systemTime);    //And now print the system time    ShowMessage(DateTimeToStr(SystemTimeToDateTime(systemTime)));

Adding one second to

12/31/2008 11:59:59pm

gives

1/1/2009 12:00:00am

rather than

1/1/2009 11:59:60pm

Q.E.D.

Original poster might not like it, but god intentionally rigged it so that a year is not evenly divisible by a day. He did it just to screw up programmers.

There can be no single answer to this question without first deciding: What is the Windows FILETIME actually counting? The Microsoft docs say it counts 100 nanosecond intervals since 1601 UTC, but this is problematic.

No form of internationally coordinated time existed prior to the year 1960. The name UTC itself does not occur in any literature prior to 1964. The name UTC as an official designation did not exist until 1970. But it gets worse. The Royal Greenwich Observatory was not established until 1676, so even trying to interpret the FILETIME as GMT has no clear meaning, and it was only around then that pendulum clocks with accurate escapements began to give accuracies of 1 second.

If FILETIME is interpreted as mean solar seconds then the number of leap seconds since 1601 is zero, for UT has no leap seconds. If FILETIME is interpreted as if there had been atomic chronometers then the number of leap seconds since 1601 is about -60 (that's negative 60 leap seconds).

That is ancient history, what about the era since atomic chronometers? It is no better because national governments have not made the distinction between mean solar seconds and SI seconds. For a decade the ITU-R has been discussing abandoning leap seconds, but they have not achieved international consensus. Part of the reason for that can be seen in thejavascript on this page (also see the delta-T link on that page for plots of the ancient history). Because national governments have not made a clear distinction, any attempt to define the count of seconds since 1972 runs the risk of being invalid according to the laws of some jurisdiction. The delegates to ITU-R are aware of this complexity, as are the folks on the POSIX committee. Until the diplomatic issues are worked out, until national governments and international standards make a clear distinction and choice between mean solar and SI seconds, there is little hope that the computer standards can follow suit.

Here's some more info about why that particular date was chosen.

The FILETIME structure records time in the form of 100-nanosecond intervals since January 1, 1601. Why was that date chosen?

The Gregorian calendar operates on a 400-year cycle, and 1601 is the first year of the cycle that was active at the time Windows NT was being designed. In other words, it was chosen to make the math come out nicely.

I actually have the email from Dave Cutler confirming this.