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PODateTime - Strange daylight savings behaviour
 

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    <p>My local timezone is (UTC+10:00) Canberra, Melbourne, Sydney</p> <p>Sat 31-Mar-2012 15:59 UTC = Sun 01-Apr-2012 02:59 +11:00<br> Sat 31-Mar-2012 16:00 UTC = Sun 01-Apr-2012 02:00 +10:00</p> <p>Daylight savings finishes at 3 AM first Sunday in April and the clock wind back 1 hour.</p> <p>Given the following code ....</p> <pre><code>DateTime dt1 = DateTime.Parse("31-Mar-2012 15:59", CultureInfo.CurrentCulture, DateTimeStyles.AssumeUniversal); DateTime dt2 = DateTime.Parse("31-Mar-2012 15:59", CultureInfo.CurrentCulture, DateTimeStyles.AssumeUniversal).AddMinutes(1); DateTime dt3 = DateTime.Parse("31-Mar-2012 16:00", CultureInfo.CurrentCulture, DateTimeStyles.AssumeUniversal); Console.WriteLine("{0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt1); Console.WriteLine("{0:yyyy-MMM-dd HH:mm:ss.ffff K} ({1}) = {2:yyyy-MMM-dd HH:mm:ss.ffff K} ({3})", dt2, dt2.Kind, dt3, dt3.Kind); Console.WriteLine("{0} : {1} : {2}", dt1.ToUniversalTime().Hour, dt2.ToUniversalTime().Hour, dt3.ToUniversalTime().Hour); </code></pre> <p>I get the following output</p> <p>2012-Apr-01 02:59:00.0000 +11:00<br> 2012-Apr-01 03:00:00.0000 +10:00 (Local) = 2012-Apr-01 02:00:00.0000 +10:00 (Local)<br> 15 : 17 : 16</p> <p>Adding 1 minute to the original datetime makes the local time 3AM but also set the offset to +10 hours. Adding 1 minute to the UTC date and parsing correctly sets the local time to 2 AM with a +10 UTC offset.</p> <p>Repeating with</p> <pre><code>DateTime dt1 = new DateTime(2012, 03, 31, 15, 59, 0, DateTimeKind.Utc); DateTime dt2 = new DateTime(2012, 03, 31, 15, 59, 0, DateTimeKind.Utc).AddMinutes(1); DateTime dt3 = new DateTime(2012, 03, 31, 16, 0, 0, DateTimeKind.Utc); </code></pre> <p>or</p> <pre><code>DateTime dt1 = DateTime.Parse("31-Mar-2012 15:59", CultureInfo.CurrentCulture, DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal); DateTime dt2 = DateTime.Parse("31-Mar-2012 15:59", CultureInfo.CurrentCulture, DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal).AddMinutes(1); DateTime dt3 = DateTime.Parse("31-Mar-2012 16:00", CultureInfo.CurrentCulture, DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal); </code></pre> <p>gives</p> <p>2012-Mar-31 15:59:00.0000 Z<br> 2012-Mar-31 16:00:00.0000 Z (Utc) = 2012-Mar-31 16:00:00.0000 Z (Utc)<br> 15 : 16 : 16 </p> <p>as expected</p> <p>Repeating again with</p> <pre><code>DateTime dt1 = new DateTime(2012, 03, 31, 15, 59, 0, DateTimeKind.Utc).ToLocalTime(); DateTime dt2 = new DateTime(2012, 03, 31, 15, 59, 0, DateTimeKind.Utc).ToLocalTime().AddMinutes(1); DateTime dt3 = new DateTime(2012, 03, 31, 16, 0, 0, DateTimeKind.Utc).ToLocalTime(); </code></pre> <p>gives the original</p> <p>2012-Apr-01 02:59:00.0000 +11:00<br> 2012-Apr-01 03:00:00.0000 +10:00 (Local) = 2012-Apr-01 02:00:00.0000 +10:00 (Local)<br> 15 : 17 : 16 </p> <p>Can anyone explain this ?</p> <p>Indecently if I use the TimeZoneInfo to convert from UTC to AUS Eastern Standard Time I get the correct time, but I lose the offset information in the DateTime instance as the DateTime.Kind == DateTimeKind.Unspecified</p> <p>== Additional scenario to highlight</p> <p>This is just simple timespan adding, starting with an NON-ambiguous UTC date, 1 minute before Daylight savings finishes.</p> <pre><code>DateTime dt1 = new DateTime(2012, 03, 31, 15, 59, 0, DateTimeKind.Utc); DateTime dt2 = new DateTime(2012, 03, 31, 15, 59, 0, DateTimeKind.Utc).ToLocalTime(); Console.WriteLine("Original in UTC : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt1); Console.WriteLine("Original in Local : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt1.ToLocalTime()); Console.WriteLine("+ 1 Minute in Local : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt1.AddMinutes(1).ToLocalTime()); Console.WriteLine("+ 1 Minute in UTC : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt1.AddMinutes(1)); Console.WriteLine("====================================================="); Console.WriteLine("Original in UTC : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt2.ToUniversalTime()); Console.WriteLine("Original in Local : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt2); Console.WriteLine("+ 1 Minute in Local : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt2.AddMinutes(1)); Console.WriteLine("+ 1 Minute in UTC : {0:yyyy-MMM-dd HH:mm:ss.ffff K}", dt2.AddMinutes(1).ToUniversalTime()); </code></pre> <p>gives</p> <p>Original in UTC : 2012-Mar-31 15:59:00.0000 Z<br> Original in Local : 2012-Apr-01 02:59:00.0000 +11:00<br> + 1 Minute in Local : 2012-Apr-01 <strong>02</strong>:00:00.0000 +10:00<br> + 1 Minute in UTC : 2012-Mar-31 <strong>16</strong>:00:00.0000 Z</p> <p>=====================================================</p> <p>Original in UTC : 2012-Mar-31 15:59:00.0000 Z<br> Original in Local : 2012-Apr-01 02:59:00.0000 +11:00<br> + 1 Minute in Local : 2012-Apr-01 <strong>03</strong>:00:00.0000 +10:00<br> + 1 Minute in UTC : 2012-Mar-31 <strong>17</strong>:00:00.0000 Z </p>
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    1. CODateTime does NOT "keep" the local offset. I merely shows the offset that would be in effect at that time. Since dt2 is always in local time, the view it has of the current hour IS "true". You should be using DateTimeOffset if you want to carry around the "as applied" offset http://msdn.microsoft.com/en-us/library/system.datetimeoffset.aspx
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    2. CO... if that was true then I would have expected the third result from dt2 in the last scenario to be 03:00:00 +11:00, but it knows that DST has finished. It correctly switched to +10:00, but didn't take off the hour. DateTimeOffset shows the time as 03:00:00 +11:00, which is not valid for my local timezone.
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      1. USRobert Slaney
    3. CONo, it knows that YOU SAID this was 3:00 as of 4/1/2012, so the offset AT THAT moment is +10:00
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