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detect if date/time is daylight savings time

Posted on 2004-03-31
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Last Modified: 2013-11-20
Hi,

Given the following datetime string "2004-03-30 13:09:28" I need to detect if it is PST or PDT?

Dalight Savings time:
Starts: First Sunday in April at 2 am local time
Ends: Last Sunday in October at 2 am local time

What I need to do is append PST or PDT accordingly.

Thanks,
Alex
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Question by:astankovic
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4 Comments
 
LVL 14

Accepted Solution

by:
wayside earned 2000 total points
ID: 10727902
int startday = 1;
int endday = 31;

COleDateTime startDST(2004, 4, startday, 2, 0, 0);
COleDateTime endDST(2004, 10, endday, 2, 0, 0);

while (startDst.GetDayOfWeek() != 1) {
  startday++;
  startDST.SetDate(2004, 4, startday);
}

while (endDst.GetDayOfWeek() != 1) {
  endday--;
  endDST.SetDate(2004, 10, endday);
}

// now startDST and endDST contain the start and end dates of daylight savings time
COleDateTime testDate(2004, 6, 12, 12, 34, 56);

if (testDate >= startDST && testDate <= endDST) {
  printf("PDT");
}
else {
  printf("PST");
}
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LVL 14

Expert Comment

by:wayside
ID: 10727913
More generally, you would extract the year out of your test date and use that when building the dates for startDST and endDST.
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Author Comment

by:astankovic
ID: 10728216
Thanks!
0
 
LVL 5

Expert Comment

by:jerry_jeremiah
ID: 10731004
Hello,

Those times you mention for DST are very specifically USA and Canada only - in fact it doesn't even really apply to all of the USA and Canada because Fort St. John, Charlie Lake, Taylor and Dawson Creek in British Columbia, Creston in the East Kootenays, and most of  Saskatchewan (except Denare Beach and Creighton) don't use daylight savings time at all.

Just to confuse things, the UK switches at one o'clock in the morning the last Sunday in March and two o'clock in the morning in October.  New Zealand did their switchover three weeks ago and Australia did their's the week after that.  Besides which, any region in the southern hemisphere that does daylight savings time does it at the opposite time of the year (Autumn here in New Zealand is in March/April)

Jerry
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