Re: Daylight Saving Time
William <port@mx15.freecom.ne.jp> wrote:
I am making an application to show the local time of some cities in
the world. It seems to me Daylight Saving Time doesn't work well on
the local time of London. The code is as follows,
{
//get GMT
SYSTEMTIME sGMT;
GetSystemTime(&sGMT);
//automatically computes whether standard time or daylight savings
time CTime tUTC(sGMT,-1);
//calculate Tokyo Time
CTime tTokyo = tUTC + CTimeSpan(0,9,0,0);
ShowThisTime(IDC_EDIT2, tTokyo);
//calculate London Time
CTime tLondon = tUTC + CTimeSpan(0,0,0,0);
ShowThisTime(IDC_EDIT3, tLondon);
If I test it at Tokyo at 17:10, the London time is showed at 08:10
while the correct time should be 09:10.
And what time does it show for Tokyo? Is it correct? Looking at your
code, the times actually shown for London and Tokyo should always be 9
hours apart, independent of any DST rules. They may be wrong at either
or both ends, but they should be 9 hours apart nevertheless. Your code
does simple math on them that does not involve any DST calculations.
Do you want to show current time at a particular location adjusted for
DST in effect _at that location_ ? It is surprisingly difficult. See
http://www.codeproject.com/dotnet/WorldClock.asp
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925