datetime question (Dr. Stockton?)

JRS: In article <lxGLe.2417$Hf6.732@trndny07>, dated Sun, 14 Aug 2005
12:10:57, seen in news:alt.comp.lang.borland-delphi, DAVID B MORGAN
<lepton2deletethis@xxxxxxxxxxx> posted :

>As some of you may or may not have heard the U.S. is going to change the
>dates for Daylight Savings Time.

Is it? I have read that Congress has passed the proposal, but I have
not read that the proposal has completed the process and been signed
into law by, I suppose, GWB.

>Beginning in 2007 daylight time will start three weeks earlier

No; three or four weeks, AIUI. I think three in 2007; four in 2008,
2009; 3 in 2010 2011 2012; 4 ...

> and end it a
>week later in a bid to save energy.

And possibly to put Halloween in DST. It will also make Summer a fixed
number of weeks long, but not Winter.

>My question is will this affect the accuracy of any of Delphi's datetime
>functions?

Delphi knows nothing of the matter, AFAIK (may be different in later
versions); but a Delphi program can access the OS version of the
information, as in <URL:http://www.merlyn.demon.co.uk/programs/tz-
check.pas>.

System data will need to be updated, between the last Sunday in Oct 2006
and the second Sunday in March 2007, or else those that get the time
from Net servers etc. will have the correct GMT but the wrong LCT during
the discrepant weeks.

After the update I expect that it will no longer be possible to use the
OS rules to compute US DST for years 1987-2006, unless system code is
also changed.

Fortunately, the probable form of the rules will not permit a setting of
"3 weeks before current".

Of course, Borland should be asked for an authoritative answer.

It may be necessary to produce code to transfer a UTC time to/from a US
civil time in a given zone covering the range 1987 to 2007+ ; it will
need to have new and old rules coded in, and parameters for time zone
and whether DST is used, and the date of any change in the use of DST
(for some Indianans, AIUI). ISTM best, given the general standard of
date library code, for it to be written and debugged in public, for
example here or in the Borland newsgroups.

It should be an amusing exercise, at least for non-participants.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
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