Mega Code Archive
Difference between time zones
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To calculate the difference between two timezones e.g. between your computer's local time and Greenwich Mean Time (GMT) you can use GetTimeZoneInformation.
There are two ways to convert a TDateTime value between local time and GMT:
GetTimeZoneInformation and LocalFileTimeToFileTime.
The code below bases on GetTimeZoneInformation.
unit TimeZoneConversion;
interface
uses
Windows, SysUtils;
function LocaleDateTimeToGMTDateTime(const Value: TDateTime) : TDateTime;
function GMTDateTimeToLocaleDateTime(const Value: TDateTime) : TDateTime;
implementation
const
MinsPerDay = 24*60;
function GetGMTBias : Integer;
var
info: TTimeZoneInformation;
Mode: DWord;
begin
Mode := GetTimeZoneInformation(info);
Result := info.Bias;
case Mode of
TIME_ZONE_ID_INVALID:
begin
RaiseLastWin32Error
end;
TIME_ZONE_ID_STANDARD:
begin
Result := Result+info.StandardBias
end;
TIME_ZONE_ID_DAYLIGHT:
begin
Result := Result+info.DaylightBias
end;
end;
end;
function LocaleDateTimeToGMTDateTime(const Value: TDateTime) : TDateTime;
begin
Result := Value+(GetGMTBias/MinsPerDay);
end;
function GMTDateTimeToLocaleDateTime(const Value: TDateTime) : TDateTime;
begin
Result := Value-(GetGMTBias/MinsPerDay);
end;
end.
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