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#134: How read the daylight saving time?

Sometimes from code you want to find out if MS Windows is operating in saylight saving time. For example, I used this code in own GroupMail because in message header you must include a timestamp.

The code below allow to solve this task:

uses Windows;

const
  TIME_ZONE_ID_UNKNOWN  = 0;
  TIME_ZONE_ID_STANDARD = 1;
  TIME_ZONE_ID_DAYLIGHT = 2;

var
  tz : TTimeZoneInformation;
begin
  case GetTimeZoneInformation(tz) of
    TIME_ZONE_ID_STANDARD: ShowMessage(tz.StandardName);
    TIME_ZONE_ID_DAYLIGHT: ShowMessage(tz.DaylightName);
  else
    ShowMessage('Unknown state');
  end;
end;

Also I want to say that similar code you can use for BIAS reading (offset to UTC/GMT in minutes of local time zone):

function GetTimeZoneBias: Integer;
var
  tz: TTimeZoneInformation;
begin
  case GetTimeZoneInformation(tz) of
    TIME_ZONE_ID_STANDARD: Result := -(tz.StandardBias + tz.Bias) div (24*60);
    TIME_ZONE_ID_DAYLIGHT: Result := -(tz.DaylightBias + tz.Bias) div (24*60);
  else
    Result := 0;
  end;
end;

If the result is 0 then time is a GMT. Else you'll receive a difference as positive or negative value.

Published: December 12, 2001

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