Question

I am using DateTime.ToLocalTime() to convert dates from UTC to local time. My time zone is GMT+1(Belgrade, Budapest, Lubjna…), it is set properly in Windows Settings (XP).

Last weekend in our time zone we changed to winter time to summer time, it means, we set back local time by one hour.

As I see ToLocalTime method behaves strange from that moment. When I use it to convert dates that are after this winter time change, it works great, like this:

var utcDate2 = new DateTime(2011, 11, 2, 9, 0, 0,DateTimeKind.Utc);

utcDate1.ToLocalTime() value is: 2011.11.02. 10:00:00 it is correct

Burt when I want to convert a date before this change (e.g. a date from summer time) it gives back a bad value like this:

var utcDate1 = new DateTime(2011, 10, 23, 9, 0, 0,DateTimeKind.Utc);

utcDate2.ToLocalTime() value is: 2011.10.23. 10:00:00 it is incorrect It should be 2011.10.23. 11:00:00

What should I do to get correct values? How should I use ToLocalTime that also adjust winter/summer time?

Answer 1

http://msdn.microsoft.com/en-us/library/system.datetime.tolocaltime.aspx

On Windows XP systems, the ToLocalTime method recognizes only the
current adjustment rule when converting from UTC to local time. As a
result, conversions for periods before the current adjustment rule
came into effect may not accurately reflect the difference between UTC
and local time.

So you will have to find another way to figure it out.