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DYNAMIC_TIME_ZONE_INFORMATION structure

Specifies settings for a time zone and dynamic daylight saving time.

Syntax


typedef struct _TIME_DYNAMIC_ZONE_INFORMATION {
  LONG       Bias;
  WCHAR      StandardName[32];
  SYSTEMTIME StandardDate;
  LONG       StandardBias;
  WCHAR      DaylightName[32];
  SYSTEMTIME DaylightDate;
  LONG       DaylightBias;
  WCHAR      TimeZoneKeyName[128];
  BOOLEAN    DynamicDaylightTimeDisabled;
} DYNAMIC_TIME_ZONE_INFORMATION, *PDYNAMIC_TIME_ZONE_INFORMATION;

Members

Bias

The current bias for local time translation on this computer, in minutes. The bias is the difference, in minutes, between Coordinated Universal Time (UTC) and local time. All translations between UTC and local time are based on the following formula:

UTC = local time + bias

This member is required.

StandardName

A description for standard time. For example, "EST" could indicate Eastern Standard Time. The string will be returned unchanged by the GetDynamicTimeZoneInformation function. This string can be empty.

StandardDate

A SYSTEMTIME structure that contains a date and local time when the transition from daylight saving time to standard time occurs on this operating system. If the time zone does not support daylight saving time or if the caller needs to disable daylight saving time, the wMonth member in the SYSTEMTIME structure must be zero. If this date is specified, the DaylightDate member of this structure must also be specified. Otherwise, the system assumes the time zone data is invalid and no changes will be applied.

To select the correct day in the month, set the wYear member to zero, the wHour and wMinute members to the transition time, the wDayOfWeek member to the appropriate weekday, and the wDay member to indicate the occurrence of the day of the week within the month (1 to 5, where 5 indicates the final occurrence during the month if that day of the week does not occur 5 times).

Using this notation, specify 02:00 on the first Sunday in April as follows: wHour = 2, wMonth = 4, wDayOfWeek = 0, wDay = 1. Specify 02:00 on the last Thursday in October as follows: wHour = 2, wMonth = 10, wDayOfWeek = 4, wDay = 5.

If the wYear member is not zero, the transition date is absolute; it will only occur one time. Otherwise, it is a relative date that occurs yearly.

StandardBias

The bias value to be used during local time translations that occur during standard time. This member is ignored if a value for the StandardDate member is not supplied.

This value is added to the value of the Bias member to form the bias used during standard time. In most time zones, the value of this member is zero.

DaylightName

A description for daylight saving time (DST). For example, "PDT" could indicate Pacific Daylight Time. The string will be returned unchanged by the GetDynamicTimeZoneInformation function. This string can be empty.

DaylightDate

A SYSTEMTIME structure that contains a date and local time when the transition from standard time to daylight saving time occurs on this operating system. If the time zone does not support daylight saving time or if the caller needs to disable daylight saving time, the wMonth member in the SYSTEMTIME structure must be zero. If this date is specified, the StandardDate member in this structure must also be specified. Otherwise, the system assumes the time zone data is invalid and no changes will be applied.

To select the correct day in the month, set the wYear member to zero, the wHour and wMinute members to the transition time, the wDayOfWeek member to the appropriate weekday, and the wDay member to indicate the occurrence of the day of the week within the month (1 to 5, where 5 indicates the final occurrence during the month if that day of the week does not occur 5 times).

If the wYear member is not zero, the transition date is absolute; it will only occur one time. Otherwise, it is a relative date that occurs yearly.

DaylightBias

The bias value to be used during local time translations that occur during daylight saving time. This member is ignored if a value for the DaylightDate member is not supplied.

This value is added to the value of the Bias member to form the bias used during daylight saving time. In most time zones, the value of this member is –60.

TimeZoneKeyName

The name of the time zone registry key on the local computer. For more information, see Remarks.

DynamicDaylightTimeDisabled

Indicates whether dynamic daylight saving time is disabled. Setting this member to TRUE disables dynamic daylight saving time, causing the system to use a fixed set of transition dates.

To restore dynamic daylight saving time, call the SetDynamicTimeZoneInformation function with DynamicDaylightTimeDisabled set to FALSE. The system will read the transition dates for the current year at the next time update, the next system reboot, or the end of the calendar year (whichever comes first.)

When calling the GetDynamicTimeZoneInformation function, this member is TRUE if the time zone was set using the SetTimeZoneInformation function instead of SetDynamicTimeZoneInformation or if the user has disabled this feature using the Date and Time application in Control Panel.

To disable daylight saving time, set this member to TRUE, clear the StandardDate and DaylightDate members, and call SetDynamicTimeZoneInformation. To restore daylight saving time, call SetDynamicTimeZoneInformation with DynamicDaylightTimeDisabled set to FALSE.

Remarks

Dynamic daylight saving time provides support for time zones whose boundaries for daylight saving time change from year to year. This feature enables easier updating of systems, especially for locales where the yearly DST boundaries are known in advance. After the time zone has been updated, the current time zone setting is applied to all time operations, even when the time in question occurred before the time zone changed. Therefore, it is best to store UTC times and convert them to the current local time zone.

You can set the transition dates for the current year using the SetDynamicTimeZoneInformation function. To set future transition dates, you must add entries to the registry data. The settings for dynamic daylight time are stored in the following registry key:

HKEY_LOCAL_MACHINE
   SOFTWARE
      Microsoft
         Windows NT
            CurrentVersion
               Time Zones
                  time_zone_name
                     Dynamic DST

Each Dynamic DST key includes the following registry values.

Registry valueTypeDescription
FirstEntryREG_DWORDThe first year in the table.
LastEntryREG_DWORDThe last year in the table.
year1REG_BINARY

The following time zone information.

typedef struct _REG_TZI_FORMAT
{
    LONG Bias;
    LONG StandardBias;
    LONG DaylightBias;
    SYSTEMTIME StandardDate;
    SYSTEMTIME DaylightDate;
} REG_TZI_FORMAT;
year2REG_BINARYA REG_TZI_FORMAT structure.
yearNREG_BINARYA REG_TZI_FORMAT structure.

 

For more information on other values in the Time Zones key, see TIME_ZONE_INFORMATION.

Both StandardName and DaylightName are localized according to the current user default UI language.

Requirements

Minimum supported client

Windows Vista [desktop apps | Windows Store apps]

Minimum supported server

Windows Server 2008 [desktop apps | Windows Store apps]

Header

WinBase.h (include Windows.h)

See also

GetDynamicTimeZoneInformation
SetDynamicTimeZoneInformation
SYSTEMTIME

 

 

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