From: pandeng@telepath.com (Steve Schafer (TeamB))
Subject: Re: TFileTime to TDateTime conversion
Date: 05 Oct 1999 00:00:00 GMT
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On Tue, 5 Oct 1999 13:39:03 +0200, "Romain Petges"
<romain.petges@baloise.lu> wrote:

>does  anybody know how I can convert a TFileTime type to TDateTime.
>TFileTime is used by many Win32 API functions.

There are a couple of straightforward ways to do it; both of them are
somewhat convoluted. The conceptually simplest way is to use
FileTimeToSystemTime to reformat the time into a SYSTEMTIME structure,
and then use EncodeDate and EncodeTime to convert the resulting fields
to TDateTime.

The quicker way is to use FileTimeToDosDateTime to convert the time to
DOS date/time format, combine the two resulting fields into a LongInt
(with the date in the upper half), and then pass the result to
FileDateToDateTime.

But the best way of all is to realize that TFileTime and TDateTime are
both linear representations of time, albeit with different rates and
start points. Therefore, you can do a simple affine transformation to
convert one to the other:

 function Win32FileTimeToDateTime(Time: TFileTime): TDateTime;
   begin
   Result := (Time.dwLowDateTime / 86400.0E7) +
     (Time.dwHighDateTime * 65536.0 * 65536.0 / 86400.0E7) -
     109205 end;

Note that no matter which method you use, TFileTime stores its values
as UTC, so you'll have to add or subtract an appropriate number of
hours to convert to local time.

-Steve