Detect if the DST is currently enabled

Question

I need to find an easy way to know if the local machine's 'automatically adjust clock for Daylight Saving Time' option is enabled. If the option's on, I need to know whether it is currently applied (i.e. is it DST currently in the system). Thanks in advance

score 8 · Accepted Answer · edited May 15 '16 at 07:35

8

You can find the current system default time zone and whether it is currently using DST (Daylight Saving Time) like this (.NET 3.5 onwards):

TimeZoneInfo zone = TimeZoneInfo.Local;
if (zone.SupportsDaylightSavingTime)
{
    Console.WriteLine("System default zone uses DST...");
    Console.WriteLine("In DST? {0}", zone.IsDaylightSavingTime(DateTime.UtcNow));       
}
else
{
    Console.WriteLine("System default zone does not use DST.");
}

edited May 15 '16 at 07:35

Jsinh

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answered Mar 30 '12 at 06:26

Jon Skeet

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What about using DateTime.IsDaylightSavingTime? – ABH Mar 30 '12 at 06:35
2

@hamad: Gosh, I'd never even seen that. Personally I *wouldn't* use it, because a) it doesn't tell you whether the current time zone even supports DST; b) you're really asking a question which is logically about a time zone at a particular point in time - it's a lot more flexible to use the sort of code I've presented IMO; c) it doesn't use the ghastly "let's just use the system default time zone implicitly" aspect of `DateTime`. I'm not a fan of `DateTime`, for various reasons... – Jon Skeet Mar 30 '12 at 06:42

score 2 · Answer 2 · answered Apr 18 '16 at 08:29

Here is another example in C#

private static bool IsDayLightSavingsEnabled()
{
  try
  {
    var result = Registry.GetValue(@"HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation", "DynamicDaylightTimeDisabled", 1);
    return !Convert.ToBoolean(result); //0 - Checked/enabled,  1 - Unchecked/disabled
  }
  catch
  { }
  return false;
}

score 2 · Answer 3 · answered Mar 30 '12 at 07:02

2

Another option may be is DateTime.IsDaylightSavingTime method. Check MSDN.

if (DateTime.Now.IsDaylightSavingTime())
    Console.WriteLine("Daylight Saving");
else
    Console.WriteLine("No Daylight Saving");

answered Mar 30 '12 at 07:02

ABH

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score 2 · Answer 4 · edited Jul 24 '12 at 12:24

2

You can read the registry to determine if the checkbox is checked or not. Read this key,

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation DynamicDaylightTimeDisabled

= 0 or 1 (disabled)

So something like :

    Dim retval As Object = Microsoft.Win32.Registry.GetValue("HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation", "DynamicDaylightTimeDisabled", 0)
    If retval IsNot Nothing Then
        Select Case CInt(retval)
            Case 0
                Trace.WriteLine("Automatically adjust clock for Daylight Saving Time is checked")
            Case 1
                Trace.WriteLine("Automatically adjust clock for Daylight Saving Time is NOT checked")
        End Select
    End If

edited Jul 24 '12 at 12:24

Dor Cohen

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answered Mar 30 '12 at 15:52

Dbadge

31
2

This tells if the check box is enabled, but does not tell if DST is currently in effect. – Moby Disk Aug 12 '14 at 20:40
perhaps that's what some of us want. I am running a report full of utc dates and if i did not know the state of that checkbox, and account for it, timezoneinfo will always convert based on it being checked. – John Lord May 20 '20 at 14:41

Detect if the DST is currently enabled

4 Answers4

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