ICU 76.1: icu::TimeZone Class Reference

ICU 76.1 76.1

Public Types | Public Member Functions | Static Public Member Functions | Protected Member Functions | Static Protected Member Functions | Friends
icu::TimeZone Class Referenceabstract

`TimeZone` represents a time zone offset, and also figures out daylight savings. More...

`#include <timezone.h>`

Inheritance diagram for icu::TimeZone:

## Public Types
enum | EDisplayType { SHORT = 1 , LONG , SHORT_GENERIC , LONG_GENERIC , SHORT_GMT , LONG_GMT , SHORT_COMMONLY_USED , GENERIC_LOCATION }
| Enum for use with getDisplayName. More...

## Public Member Functions
virtual | ~TimeZone ()
virtual bool | operator== (const TimeZone &that) const
| Returns true if the two TimeZones are equal.
bool | operator!= (const TimeZone &that) const
| Returns true if the two TimeZones are NOT equal; that is, if operator==() returns false.
virtual int32_t | getOffset (uint8_t era, int32_t year, int32_t month, int32_t day, uint8_t dayOfWeek, int32_t millis, UErrorCode &status) const =0
| Returns the TimeZone's adjusted GMT offset (i.e., the number of milliseconds to add to GMT to get local time in this time zone, taking daylight savings time into account) as of a particular reference date.
virtual int32_t | getOffset (uint8_t era, int32_t year, int32_t month, int32_t day, uint8_t dayOfWeek, int32_t milliseconds, int32_t monthLength, UErrorCode &status) const =0
| Gets the time zone offset, for current date, modified in case of daylight savings.
virtual void | getOffset (UDate date, UBool local, int32_t &rawOffset, int32_t &dstOffset, UErrorCode &ec) const
| Returns the time zone raw and GMT offset for the given moment in time.
virtual void | setRawOffset (int32_t offsetMillis)=0
| Sets the TimeZone's raw GMT offset (i.e., the number of milliseconds to add to GMT to get local time, before taking daylight savings time into account).
virtual int32_t | getRawOffset () const =0
| Returns the TimeZone's raw GMT offset (i.e., the number of milliseconds to add to GMT to get local time, before taking daylight savings time into account).
UnicodeString & | getID (UnicodeString &ID) const
| Fills in "ID" with the TimeZone's ID.
void | setID (const UnicodeString &ID)
| Sets the TimeZone's ID to the specified value.
UnicodeString & | getDisplayName (UnicodeString &result) const
| Returns a name of this time zone suitable for presentation to the user in the default locale.
UnicodeString & | getDisplayName (const Locale &locale, UnicodeString &result) const
| Returns a name of this time zone suitable for presentation to the user in the specified locale.
UnicodeString & | getDisplayName (UBool inDaylight, EDisplayType style, UnicodeString &result) const
| Returns a name of this time zone suitable for presentation to the user in the default locale.
UnicodeString & | getDisplayName (UBool inDaylight, EDisplayType style, const Locale &locale, UnicodeString &result) const
| Returns a name of this time zone suitable for presentation to the user in the specified locale.
virtual UBool | useDaylightTime () const =0
| Queries if this time zone uses daylight savings time.
virtual UBool | inDaylightTime (UDate date, UErrorCode &status) const =0
| Queries if the given date is in daylight savings time in this time zone.
virtual UBool | hasSameRules (const TimeZone &other) const
| Returns true if this zone has the same rule and offset as another zone.
virtual TimeZone * | clone () const =0
| Clones TimeZone objects polymorphically.
virtual UClassID | getDynamicClassID () const override=0
| Returns a unique class ID POLYMORPHICALLY.
virtual int32_t | getDSTSavings () const
| Returns the amount of time to be added to local standard time to get local wall clock time.
Public Member Functions inherited from icu::UObject
virtual | ~UObject ()
| Destructor.

## Static Public Member Functions
static const TimeZone & | getUnknown ()
| Returns the "unknown" time zone.
static const TimeZone * | getGMT ()
| The GMT (=UTC) time zone has a raw offset of zero and does not use daylight savings time.
static TimeZone * | createTimeZone (const UnicodeString &ID)
| Creates a `TimeZone` for the given ID.
static StringEnumeration * | createTimeZoneIDEnumeration (USystemTimeZoneType zoneType, const char *region, const int32_t *rawOffset, UErrorCode &ec)
| Returns an enumeration over system time zone IDs with the given filter conditions.
static StringEnumeration * | createEnumeration ()
| Returns an enumeration over all recognized time zone IDs.
static StringEnumeration * | createEnumeration (UErrorCode &status)
| Returns an enumeration over all recognized time zone IDs.
static StringEnumeration * | createEnumeration (int32_t rawOffset)
| Returns an enumeration over time zone IDs with a given raw offset from GMT.
static StringEnumeration * | createEnumerationForRawOffset (int32_t rawOffset, UErrorCode &status)
| Returns an enumeration over time zone IDs with a given raw offset from GMT.
static StringEnumeration * | createEnumeration (const char *region)
| Returns an enumeration over time zone IDs associated with the given region.
static StringEnumeration * | createEnumerationForRegion (const char *region, UErrorCode &status)
| Returns an enumeration over time zone IDs associated with the given region.
static int32_t | countEquivalentIDs (const UnicodeString &id)
| Returns the number of IDs in the equivalency group that includes the given ID.
static const UnicodeString | getEquivalentID (const UnicodeString &id, int32_t index)
| Returns an ID in the equivalency group that includes the given ID.
static TimeZone * | detectHostTimeZone ()
| Creates an instance of TimeZone detected from the current host system configuration.
static TimeZone * | createDefault ()
| Creates a new copy of the default TimeZone for this host.
static TimeZone * | forLocaleOrDefault (const Locale &locale)
| If the locale contains the timezone keyword, creates a copy of that TimeZone.
static void | adoptDefault (TimeZone *zone)
| Sets the default time zone (i.e., what's returned by createDefault()) to be the specified time zone.
static void | setDefault (const TimeZone &zone)
| Same as adoptDefault(), except that the TimeZone object passed in is NOT adopted; the caller remains responsible for deleting it.
static const char * | getTZDataVersion (UErrorCode &status)
| Returns the timezone data version currently used by ICU.
static UnicodeString & | getCanonicalID (const UnicodeString &id, UnicodeString &canonicalID, UErrorCode &status)
| Returns the canonical system timezone ID or the normalized custom time zone ID for the given time zone ID.
static UnicodeString & | getCanonicalID (const UnicodeString &id, UnicodeString &canonicalID, UBool &isSystemID, UErrorCode &status)
| Returns the canonical system time zone ID or the normalized custom time zone ID for the given time zone ID.
static UnicodeString & | getIanaID (const UnicodeString &id, UnicodeString &ianaID, UErrorCode &status)
| Returns the preferred time zone ID in the IANA time zone database for the given time zone ID.
static UnicodeString & | getWindowsID (const UnicodeString &id, UnicodeString &winid, UErrorCode &status)
| Converts a system time zone ID to an equivalent Windows time zone ID.
static UnicodeString & | getIDForWindowsID (const UnicodeString &winid, const char *region, UnicodeString &id, UErrorCode &status)
| Converts a Windows time zone ID to an equivalent system time zone ID for a region.
static UClassID | getStaticClassID ()
| Return the class ID for this class.
static int32_t | getRegion (const UnicodeString &id, char *region, int32_t capacity, UErrorCode &status)
| Gets the region code associated with the given system time zone ID.
static const char16_t * | getRegion (const UnicodeString &id, UErrorCode &status)
| Returns the region code associated with the given zone, or nullptr if the zone is not known.

## Protected Member Functions
| TimeZone ()
| Default constructor.
| TimeZone (const UnicodeString &id)
| Construct a TimeZone with a given ID.
| TimeZone (const TimeZone &source)
| Copy constructor.
TimeZone & | operator= (const TimeZone &right)
| Default assignment operator.

## Static Protected Member Functions
static UResourceBundle * | loadRule (const UResourceBundle *top, const UnicodeString &ruleid, UResourceBundle *oldbundle, UErrorCode &status)
| Utility function.

## Friends
class | ZoneMeta
class | TZEnumeration

## Detailed Description

`TimeZone` represents a time zone offset, and also figures out daylight savings.

Typically, you get a `TimeZone` using `createDefault` which creates a `TimeZone` based on the time zone where the program is running. For example, for a program running in Japan, `createDefault` creates a `TimeZone` object based on Japanese Standard Time.

You can also get a `TimeZone` using `createTimeZone` along with a time zone ID. For instance, the time zone ID for the US Pacific Time zone is "America/Los_Angeles". So, you can get a Pacific Time `TimeZone` object with:

>     TimeZone *tz = TimeZone::createTimeZone("America/Los_Angeles");

You can use the `createEnumeration` method to iterate through all the supported time zone IDs, or the `getCanonicalID` method to check if a time zone ID is supported or not. You can then choose a supported ID to get a `TimeZone`. If the time zone you want is not represented by one of the supported IDs, then you can create a custom time zone ID with the following syntax:

>     GMT[+|-]hh[[:]mm]

For example, you might specify GMT+14:00 as a custom time zone ID. The `TimeZone` that is returned when you specify a custom time zone ID uses the specified offset from GMT(=UTC) and does not observe daylight saving time. For example, you might specify GMT+14:00 as a custom time zone ID to create a TimeZone representing 14 hours ahead of GMT (with no daylight saving time). In addition, `getCanonicalID` can also be used to normalize a custom time zone ID.

TimeZone is an abstract class representing a time zone. A TimeZone is needed for Calendar to produce local time for a particular time zone. A TimeZone comprises three basic pieces of information:

- A time zone offset; that, is the number of milliseconds to add or subtract from a time expressed in terms of GMT to convert it to the same time in that time zone (without taking daylight savings time into account).
- Logic necessary to take daylight savings time into account if daylight savings time is observed in that time zone (e.g., the days and hours on which daylight savings time begins and ends).
- An ID. This is a text string that uniquely identifies the time zone.

(Only the ID is actually implemented in TimeZone; subclasses of TimeZone may handle daylight savings time and GMT offset in different ways. Currently we have the following TimeZone subclasses: RuleBasedTimeZone, SimpleTimeZone, and VTimeZone.)

The TimeZone class contains a static list containing a TimeZone object for every combination of GMT offset and daylight-savings time rules currently in use in the world, each with a unique ID. Each ID consists of a region (usually a continent or ocean) and a city in that region, separated by a slash, (for example, US Pacific Time is "America/Los_Angeles.") Because older versions of this class used three- or four-letter abbreviations instead, there is also a table that maps the older abbreviations to the newer ones (for example, "PST" maps to "America/Los_Angeles"). Anywhere the API requires an ID, you can use either form.

To create a new TimeZone, you call the factory function TimeZone::createTimeZone() and pass it a time zone ID. You can use the createEnumeration() function to obtain a list of all the time zone IDs recognized by createTimeZone().

You can also use TimeZone::createDefault() to create a TimeZone. This function uses platform-specific APIs to produce a TimeZone for the time zone corresponding to the client's computer's physical location. For example, if you're in Japan (assuming your machine is set up correctly), TimeZone::createDefault() will return a TimeZone for Japanese Standard Time ("Asia/Tokyo").

Definition at line 133 of file timezone.h.

## Member Enumeration Documentation

## ◆ EDisplayType

enum icu::TimeZone::EDisplayType

Enum for use with getDisplayName.

Stable
  ICU 2.4

Enumerator
SHORT | Selector for short display name. Stable ICU 2.4
LONG | Selector for long display name. Stable ICU 2.4
SHORT_GENERIC | Selector for short generic display name. Stable ICU 4.4
LONG_GENERIC | Selector for long generic display name. Stable ICU 4.4
SHORT_GMT | Selector for short display name derived from time zone offset. Stable ICU 4.4
LONG_GMT | Selector for long display name derived from time zone offset. Stable ICU 4.4
SHORT_COMMONLY_USED | Selector for short display name derived from the time zone's fallback name. Stable ICU 4.4
GENERIC_LOCATION | Selector for long display name derived from the time zone's fallback name. Stable ICU 4.4

Definition at line 675 of file timezone.h.

## Constructor & Destructor Documentation

## ◆ ~TimeZone()

virtual icu::TimeZone::~TimeZone | ( |  | ) |
| virtual

Stable
  ICU 2.0

## ◆ TimeZone() [1/3]

icu::TimeZone::TimeZone | ( |  | ) |
| protected

Default constructor.

ID is initialized to the empty string.

Stable
  ICU 2.0

## ◆ TimeZone() [2/3]

icu::TimeZone::TimeZone | ( | const UnicodeString & | id | ) |
| protected

Construct a TimeZone with a given ID.

Parameters

  id | a system time zone ID

Stable
  ICU 2.0

## ◆ TimeZone() [3/3]

icu::TimeZone::TimeZone | ( | const TimeZone & | source | ) |
| protected

Copy constructor.

Parameters

  source | the object to be copied.

Stable
  ICU 2.0

## Member Function Documentation

## ◆ adoptDefault()

static void icu::TimeZone::adoptDefault | ( | TimeZone * | zone | ) |
| static

Sets the default time zone (i.e., what's returned by createDefault()) to be the specified time zone.

If nullptr is specified for the time zone, the default time zone is set to the default host time zone. This call adopts the TimeZone object passed in; the client is no longer responsible for deleting it.

Parameters

  zone | A pointer to the new TimeZone object to use as the default.

Stable
  ICU 2.0

## ◆ clone()

virtual TimeZone * icu::TimeZone::clone | ( |  | ) | const
| pure virtual

Clones TimeZone objects polymorphically.

Clients are responsible for deleting the TimeZone object cloned.

Returns
  A new copy of this TimeZone object.

Stable
  ICU 2.0

Implemented in icu::BasicTimeZone, icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ countEquivalentIDs()

static int32_t icu::TimeZone::countEquivalentIDs | ( | const UnicodeString & | id | ) |
| static

Returns the number of IDs in the equivalency group that includes the given ID.

An equivalency group contains zones that have the same GMT offset and rules.

The returned count includes the given ID; it is always >= 1. The given ID must be a system time zone. If it is not, returns zero.

Parameters

  id | a system time zone ID

Returns
  the number of zones in the equivalency group containing 'id', or zero if 'id' is not a valid system ID

See also
  getEquivalentID

Stable
  ICU 2.0

## ◆ createDefault()

static TimeZone * icu::TimeZone::createDefault | ( |  | ) |
| static

Creates a new copy of the default TimeZone for this host.

Unless the default time zone has already been set using adoptDefault() or setDefault(), the default is determined by querying the host system configuration. If the host system detection routines fail, or if they specify a TimeZone or TimeZone offset which is not recognized, then the special TimeZone "Etc/Unknown" is instantiated and made the default.

Returns
  A default TimeZone. Clients are responsible for deleting the time zone object returned.

See also
  getUnknown

Stable
  ICU 2.0

## ◆ createEnumeration() [1/4]

static StringEnumeration * icu::TimeZone::createEnumeration | ( |  | ) |
| static

Returns an enumeration over all recognized time zone IDs.

(i.e., all strings that createTimeZone() accepts)

Returns
  an enumeration object, owned by the caller.

Deprecated
  ICU 70 Use createEnumeration(UErrorCode&) instead.

## ◆ createEnumeration() [2/4]

static StringEnumeration * icu::TimeZone::createEnumeration | ( | const char * | region | ) |
| static

Returns an enumeration over time zone IDs associated with the given region.

Some zones are affiliated with no region (e.g., "UTC"); these may also be retrieved, as a group.

Parameters

  region | The ISO 3166 two-letter country code, or nullptr to retrieve zones not affiliated with any region.

Returns
  an enumeration object, owned by the caller

Deprecated
  ICU 70 Use createEnumerationForRegion(const char*,UErrorCode&) instead.

## ◆ createEnumeration() [3/4]

static StringEnumeration * icu::TimeZone::createEnumeration | ( | int32_t | rawOffset | ) |
| static

Returns an enumeration over time zone IDs with a given raw offset from GMT.

There may be several times zones with the same GMT offset that differ in the way they handle daylight savings time. For example, the state of Arizona doesn't observe daylight savings time. If you ask for the time zone IDs corresponding to GMT-7:00, you'll get back an enumeration over two time zone IDs: "America/Denver," which corresponds to Mountain Standard Time in the winter and Mountain Daylight Time in the summer, and "America/Phoenix", which corresponds to Mountain Standard Time year-round, even in the summer.

Parameters

  rawOffset | an offset from GMT in milliseconds, ignoring the effect of daylight savings time, if any

Returns
  an enumeration object, owned by the caller

Deprecated
  ICU 70 Use createEnumerationForRawOffset(int32_t,UErrorCode&) instead.

## ◆ createEnumeration() [4/4]

static StringEnumeration * icu::TimeZone::createEnumeration | ( | UErrorCode & | status | ) |
| static

Returns an enumeration over all recognized time zone IDs.

(i.e., all strings that createTimeZone() accepts)

Parameters

  status | Receives the status.

Returns
  an enumeration object, owned by the caller.

Stable
  ICU 70

## ◆ createEnumerationForRawOffset()

static StringEnumeration * icu::TimeZone::createEnumerationForRawOffset | ( | int32_t | rawOffset,
|  | UErrorCode & | status )
| static

Returns an enumeration over time zone IDs with a given raw offset from GMT.

There may be several times zones with the same GMT offset that differ in the way they handle daylight savings time. For example, the state of Arizona doesn't observe daylight savings time. If you ask for the time zone IDs corresponding to GMT-7:00, you'll get back an enumeration over two time zone IDs: "America/Denver," which corresponds to Mountain Standard Time in the winter and Mountain Daylight Time in the summer, and "America/Phoenix", which corresponds to Mountain Standard Time year-round, even in the summer.

Parameters

  rawOffset | an offset from GMT in milliseconds, ignoring the effect of daylight savings time, if any
  status | Receives the status.

Returns
  an enumeration object, owned by the caller

Stable
  ICU 70

## ◆ createEnumerationForRegion()

static StringEnumeration * icu::TimeZone::createEnumerationForRegion | ( | const char * | region,
|  | UErrorCode & | status )
| static

Returns an enumeration over time zone IDs associated with the given region.

Some zones are affiliated with no region (e.g., "UTC"); these may also be retrieved, as a group.

Parameters

  region | The ISO 3166 two-letter country code, or nullptr to retrieve zones not affiliated with any region.
  status | Receives the status.

Returns
  an enumeration object, owned by the caller

Stable
  ICU 70

## ◆ createTimeZone()

static TimeZone * icu::TimeZone::createTimeZone | ( | const UnicodeString & | ID | ) |
| static

Creates a `TimeZone` for the given ID.

Parameters

  ID | the ID for a `TimeZone`, such as "America/Los_Angeles", or a custom ID such as "GMT-8:00".

Returns
  the specified `TimeZone`, or a mutable clone of getUnknown() if the given ID cannot be understood or if the given ID is "Etc/Unknown". The return result is guaranteed to be non-nullptr. If you require that the specific zone asked for be returned, compare the result with getUnknown() or check the ID of the return result.

Stable
  ICU 2.0

## ◆ createTimeZoneIDEnumeration()

static StringEnumeration * icu::TimeZone::createTimeZoneIDEnumeration | ( | USystemTimeZoneType | zoneType,
|  | const char * | region,
|  | const int32_t * | rawOffset,
|  | UErrorCode & | ec )
| static

Returns an enumeration over system time zone IDs with the given filter conditions.

Parameters

  zoneType | The system time zone type.
  region | The ISO 3166 two-letter country code or UN M.49 three-digit area code. When nullptr, no filtering done by region.
  rawOffset | An offset from GMT in milliseconds, ignoring the effect of daylight savings time, if any. When nullptr, no filtering done by zone offset.
  ec | Output param to filled in with a success or an error.

Returns
  an enumeration object, owned by the caller.

Stable
  ICU 4.8

## ◆ detectHostTimeZone()

static TimeZone * icu::TimeZone::detectHostTimeZone | ( |  | ) |
| static

Creates an instance of TimeZone detected from the current host system configuration.

If the host system detection routines fail, or if they specify a TimeZone or TimeZone offset which is not recognized, then the special TimeZone "Etc/Unknown" is returned.

Note that ICU4C does not change the default time zone unless `TimeZone::adoptDefault(TimeZone*)` or `TimeZone::setDefault(const TimeZone&)` is explicitly called by a user. This method does not update the current ICU's default, and may return a different TimeZone from the one returned by `TimeZone::createDefault()`.

This function is not thread safe.

Returns
  A new instance of TimeZone detected from the current host system configuration.

See also
  adoptDefault
  setDefault
  createDefault
  getUnknown

Stable
  ICU 55

## ◆ forLocaleOrDefault()

static TimeZone * icu::TimeZone::forLocaleOrDefault | ( | const Locale & | locale | ) |
| static

If the locale contains the timezone keyword, creates a copy of that TimeZone.

Otherwise, create the default timezone.

Parameters

  locale | a locale which may contains 'timezone' keyword/value.

Returns
  A TimeZone. Clients are responsible for deleting the time zone object returned.

Internal
  Do not use. This API is for internal use only.

## ◆ getCanonicalID() [1/2]

static UnicodeString & icu::TimeZone::getCanonicalID | ( | const UnicodeString & | id,
|  | UnicodeString & | canonicalID,
|  | UBool & | isSystemID,
|  | UErrorCode & | status )
| static

Returns the canonical system time zone ID or the normalized custom time zone ID for the given time zone ID.

Parameters

  id | The input time zone ID to be canonicalized.
  canonicalID | Receives the canonical system time zone ID or the custom time zone ID in normalized format.
  isSystemID | Receives if the given ID is a known system time zone ID.
  status | Receives the status. When the given time zone ID is neither a known system time zone ID nor a valid custom time zone ID, U_ILLEGAL_ARGUMENT_ERROR is set.

Returns
  A reference to the result.

Stable
  ICU 4.0

## ◆ getCanonicalID() [2/2]

static UnicodeString & icu::TimeZone::getCanonicalID | ( | const UnicodeString & | id,
|  | UnicodeString & | canonicalID,
|  | UErrorCode & | status )
| static

Returns the canonical system timezone ID or the normalized custom time zone ID for the given time zone ID.

Parameters

  id | The input time zone ID to be canonicalized.
  canonicalID | Receives the canonical system time zone ID or the custom time zone ID in normalized format.
  status | Receives the status. When the given time zone ID is neither a known system time zone ID nor a valid custom time zone ID, U_ILLEGAL_ARGUMENT_ERROR is set.

Returns
  A reference to the result.

Stable
  ICU 4.0

## ◆ getDisplayName() [1/4]

UnicodeString & icu::TimeZone::getDisplayName | ( | const Locale & | locale,
|  | UnicodeString & | result ) const

Returns a name of this time zone suitable for presentation to the user in the specified locale.

This method returns the long name, not including daylight savings. If the display name is not available for the locale, then this method returns a string in the localized GMT offset format such as `GMT[+-]HH:mm`.

Parameters

  locale | the locale in which to supply the display name.
  result | the human-readable name of this time zone in the given locale or in the default locale if the given locale is not recognized.

Returns
  A reference to 'result'.

Stable
  ICU 2.0

## ◆ getDisplayName() [2/4]

UnicodeString & icu::TimeZone::getDisplayName | ( | UBool | inDaylight,
|  | EDisplayType | style,
|  | const Locale & | locale,
|  | UnicodeString & | result ) const

Returns a name of this time zone suitable for presentation to the user in the specified locale.

If the display name is not available for the locale, then this method returns a string in the localized GMT offset format such as `GMT[+-]HH:mm`.

Parameters

  inDaylight | if true, return the daylight savings name.
  style |
  locale | the locale in which to supply the display name.
  result | the human-readable name of this time zone in the given locale or in the default locale if the given locale is not recognized.

Returns
  A reference to 'result'.

Stable
  ICU 2.0

## ◆ getDisplayName() [3/4]

UnicodeString & icu::TimeZone::getDisplayName | ( | UBool | inDaylight,
|  | EDisplayType | style,
|  | UnicodeString & | result ) const

Returns a name of this time zone suitable for presentation to the user in the default locale.

If the display name is not available for the locale, then this method returns a string in the localized GMT offset format such as `GMT[+-]HH:mm`.

Parameters

  inDaylight | if true, return the daylight savings name.
  style |
  result | the human-readable name of this time zone in the default locale.

Returns
  A reference to 'result'.

Stable
  ICU 2.0

## ◆ getDisplayName() [4/4]

UnicodeString & icu::TimeZone::getDisplayName | ( | UnicodeString & | result | ) | const

Returns a name of this time zone suitable for presentation to the user in the default locale.

This method returns the long name, not including daylight savings. If the display name is not available for the locale, then this method returns a string in the localized GMT offset format such as `GMT[+-]HH:mm`.

Parameters

  result | the human-readable name of this time zone in the default locale.

Returns
  A reference to 'result'.

Stable
  ICU 2.0

## ◆ getDSTSavings()

virtual int32_t icu::TimeZone::getDSTSavings | ( |  | ) | const
| virtual

Returns the amount of time to be added to local standard time to get local wall clock time.

The default implementation always returns 3600000 milliseconds (i.e., one hour) if this time zone observes Daylight Saving Time. Otherwise, 0 (zero) is returned.

If an underlying TimeZone implementation subclass supports historical Daylight Saving Time changes, this method returns the known latest daylight saving value.

Returns
  the amount of saving time in milliseconds

Stable
  ICU 3.6

Reimplemented in icu::SimpleTimeZone.

## ◆ getDynamicClassID()

virtual UClassID icu::TimeZone::getDynamicClassID | ( |  | ) | const
| overridepure virtual

Returns a unique class ID POLYMORPHICALLY.

This method is to implement a simple version of RTTI, since not all C++ compilers support genuine RTTI. Polymorphic operator==() and clone() methods call this method.

Concrete subclasses of TimeZone must use the UOBJECT_DEFINE_RTTI_IMPLEMENTATION macro from uobject.h in their implementation to provide correct RTTI information.

Returns
  The class ID for this object. All objects of a given class have the same class ID. Objects of other classes have different class IDs.

Stable
  ICU 2.0

Reimplemented from icu::UObject.

Implemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ getEquivalentID()

static const UnicodeString icu::TimeZone::getEquivalentID | ( | const UnicodeString & | id,
|  | int32_t | index )
| static

Returns an ID in the equivalency group that includes the given ID.

An equivalency group contains zones that have the same GMT offset and rules.

The given index must be in the range 0..n-1, where n is the value returned by `countEquivalentIDs(id)`. For some value of 'index', the returned value will be equal to the given id. If the given id is not a valid system time zone, or if 'index' is out of range, then returns an empty string.

Parameters

  id | a system time zone ID
  index | a value from 0 to n-1, where n is the value returned by `countEquivalentIDs(id)`

Returns
  the ID of the index-th zone in the equivalency group containing 'id', or an empty string if 'id' is not a valid system ID or 'index' is out of range

See also
  countEquivalentIDs

Stable
  ICU 2.0

## ◆ getGMT()

static const TimeZone * icu::TimeZone::getGMT | ( |  | ) |
| static

The GMT (=UTC) time zone has a raw offset of zero and does not use daylight savings time.

This is a commonly used time zone.

Note: For backward compatibility reason, the ID used by the time zone returned by this method is "GMT", although the ICU's canonical ID for the GMT time zone is "Etc/GMT".

Returns
  the GMT/UTC time zone.

See also
  getUnknown

Stable
  ICU 2.0

## ◆ getIanaID()

static UnicodeString & icu::TimeZone::getIanaID | ( | const UnicodeString & | id,
|  | UnicodeString & | ianaID,
|  | UErrorCode & | status )
| static

Returns the preferred time zone ID in the IANA time zone database for the given time zone ID.

There are two types of preferred IDs. The first type is the one defined in zone.tab file, such as "America/Los_Angeles". The second types is the one defined for zones not associated with a specific region, but not defined with "Link" syntax such as "Etc/GMT+10".

Note: For most of valid time zone IDs, this method returns an ID same as getCanonicalID(). getCanonicalID() is based on canonical time zone IDs defined in Unicode CLDR. These canonical time zone IDs in CLDR were based on very old version of the time zone database. In the IANA time zone database, some IDs were updated since then. This API returns a newer time zone ID. For example, CLDR defines "Asia/Calcutta" as the canonical time zone ID. This method returns "Asia/Kolkata" instead.

"Etc/Unknown" is a special time zone ID defined by CLDR. There are no corresponding zones in the IANA time zone database. Therefore, this API returns U_ILLEGAL_ARGUMENT_ERROR when the input ID is "Etc/Unknown".

Parameters

  id | The input time zone ID.
  ianaID | Receives the preferred time zone ID in the IANA time zone database. When the given time zone ID is not a known time zone ID, this method sets an invalid (bogus) string.
  status | Receives the status. When the given time zone ID is not a known time zone ID, U_ILLEGAL_ARGUMENT_ERROR is set.

Returns
  A reference to the result.

Stable
  ICU 74

## ◆ getID()

UnicodeString & icu::TimeZone::getID | ( | UnicodeString & | ID | ) | const
| inline

Fills in "ID" with the TimeZone's ID.

Parameters

  ID | Receives this TimeZone's ID.

Returns
  A reference to 'ID'

Stable
  ICU 2.0

Definition at line 1047 of file timezone.h.

## ◆ getIDForWindowsID()

static UnicodeString & icu::TimeZone::getIDForWindowsID | ( | const UnicodeString & | winid,
|  | const char * | region,
|  | UnicodeString & | id,
|  | UErrorCode & | status )
| static

Converts a Windows time zone ID to an equivalent system time zone ID for a region.

For example, system time zone ID "America/Los_Angeles" is returned for input Windows ID "Pacific Standard Time" and region "US" (or `null`), "America/Vancouver" is returned for the same Windows ID "Pacific Standard Time" and region "CA".

Not all Windows time zones can be mapped to system time zones. When the input Windows time zone ID is unknown or unmappable to a system time zone, then the result will be empty, but the operation itself remains successful (no error status set on return).

This implementation utilizes Zone-Tzid mapping data. The mapping data is updated time to time. To get the latest changes, please read the ICU user guide section Updating the Time Zone Data.

Parameters

  winid | A Windows time zone ID.
  region | A NUL-terminated region code, or `nullptr` if no regional preference.
  id | Receives a system time zone ID. When the input Windows time zone ID is unknown or unmappable to a system time zone ID, then an empty string is set on return.
  status | Receives the status.

Returns
  A reference to the result (`id`).

See also
  getWindowsID

Stable
  ICU 52

## ◆ getOffset() [1/3]

virtual void icu::TimeZone::getOffset | ( | UDate | date,
|  | UBool | local,
|  | int32_t & | rawOffset,
|  | int32_t & | dstOffset,
|  | UErrorCode & | ec ) const
| virtual

Returns the time zone raw and GMT offset for the given moment in time.

Upon return, local-millis = GMT-millis + rawOffset + dstOffset. All computations are performed in the proleptic Gregorian calendar. The default implementation in the TimeZone class delegates to the 8-argument getOffset().

Parameters

  date | moment in time for which to return offsets, in units of milliseconds from January 1, 1970 0:00 GMT, either GMT time or local wall time, depending on ‘local’.
  local | if true, ‘date’ is local wall time; otherwise it is in GMT time.
  rawOffset | output parameter to receive the raw offset, that is, the offset not including DST adjustments
  dstOffset | output parameter to receive the DST offset, that is, the offset to be added to ‘rawOffset’ to obtain the total offset between local and GMT time. If DST is not in effect, this value is zero; otherwise it is a positive value, typically one hour.
  ec | input-output error code

Stable
  ICU 2.8

Reimplemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ getOffset() [2/3]

virtual int32_t icu::TimeZone::getOffset | ( | uint8_t | era,
|  | int32_t | year,
|  | int32_t | month,
|  | int32_t | day,
|  | uint8_t | dayOfWeek,
|  | int32_t | millis,
|  | UErrorCode & | status ) const
| pure virtual

Returns the TimeZone's adjusted GMT offset (i.e., the number of milliseconds to add to GMT to get local time in this time zone, taking daylight savings time into account) as of a particular reference date.

The reference date is used to determine whether daylight savings time is in effect and needs to be figured into the offset that is returned (in other words, what is the adjusted GMT offset in this time zone at this particular date and time?). For the time zones produced by createTimeZone(), the reference data is specified according to the Gregorian calendar, and the date and time fields are local standard time.

Note: Don't call this method. Instead, call the getOffset(UDate...) overload, which returns both the raw and the DST offset for a given time. This method is retained only for backward compatibility.

Parameters

  era | The reference date's era
  year | The reference date's year
  month | The reference date's month (0-based; 0 is January)
  day | The reference date's day-in-month (1-based)
  dayOfWeek | The reference date's day-of-week (1-based; 1 is Sunday)
  millis | The reference date's milliseconds in day, local standard time
  status | Output param to filled in with a success or an error.

Returns
  The offset in milliseconds to add to GMT to get local time.

Stable
  ICU 2.0

Implemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ getOffset() [3/3]

virtual int32_t icu::TimeZone::getOffset | ( | uint8_t | era,
|  | int32_t | year,
|  | int32_t | month,
|  | int32_t | day,
|  | uint8_t | dayOfWeek,
|  | int32_t | milliseconds,
|  | int32_t | monthLength,
|  | UErrorCode & | status ) const
| pure virtual

Gets the time zone offset, for current date, modified in case of daylight savings.

This is the offset to add to UTC to get local time.

Note: Don't call this method. Instead, call the getOffset(UDate...) overload, which returns both the raw and the DST offset for a given time. This method is retained only for backward compatibility.

Parameters

  era | the era of the given date.
  year | the year in the given date.
  month | the month in the given date. Month is 0-based. e.g., 0 for January.
  day | the day-in-month of the given date.
  dayOfWeek | the day-of-week of the given date.
  milliseconds | the millis in day in standard local time.
  monthLength | the length of the given month in days.
  status | Output param to filled in with a success or an error.

Returns
  the offset to add to GMT to get local time.

Stable
  ICU 2.0

Implemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ getRawOffset()

virtual int32_t icu::TimeZone::getRawOffset | ( |  | ) | const
| pure virtual

Returns the TimeZone's raw GMT offset (i.e., the number of milliseconds to add to GMT to get local time, before taking daylight savings time into account).

Returns
  The TimeZone's raw GMT offset.

Stable
  ICU 2.0

Implemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ getRegion() [1/2]

static int32_t icu::TimeZone::getRegion | ( | const UnicodeString & | id,
|  | char * | region,
|  | int32_t | capacity,
|  | UErrorCode & | status )
| static

Gets the region code associated with the given system time zone ID.

The region code is either ISO 3166 2-letter country code or UN M.49 3-digit area code. When the time zone is not associated with a specific location, for example - "Etc/UTC", "EST5EDT", then this method returns "001" (UN M.49 area code for World).

Parameters

  id | The system time zone ID.
  region | Output buffer for receiving the region code.
  capacity | The size of the output buffer.
  status | Receives the status. When the given time zone ID is not a known system time zone ID, U_ILLEGAL_ARGUMENT_ERROR is set.

Returns
  The length of the output region code.

Stable
  ICU 4.8

## ◆ getRegion() [2/2]

static const char16_t * icu::TimeZone::getRegion | ( | const UnicodeString & | id,
|  | UErrorCode & | status )
| static

Returns the region code associated with the given zone, or nullptr if the zone is not known.

Parameters

  id | zone id string
  status | Status parameter

Returns
  the region associated with the given zone

Internal
  Do not use. This API is for internal use only.

## ◆ getStaticClassID()

static UClassID icu::TimeZone::getStaticClassID | ( |  | ) |
| static

Return the class ID for this class.

This is useful only for comparing to a return value from getDynamicClassID().

Returns
  The class ID for all objects of this class.

Stable
  ICU 2.0

## ◆ getTZDataVersion()

static const char * icu::TimeZone::getTZDataVersion | ( | UErrorCode & | status | ) |
| static

Returns the timezone data version currently used by ICU.

Parameters

  status | Output param to filled in with a success or an error.

Returns
  the version string, such as "2007f"

Stable
  ICU 3.8

## ◆ getUnknown()

static const TimeZone & icu::TimeZone::getUnknown | ( |  | ) |
| static

Returns the "unknown" time zone.

It behaves like the GMT/UTC time zone but has the `UCAL_UNKNOWN_ZONE_ID` = "Etc/Unknown". createTimeZone() returns a mutable clone of this time zone if the input ID is not recognized.

Returns
  the "unknown" time zone.

See also
  UCAL_UNKNOWN_ZONE_ID
  createTimeZone
  getGMT

Stable
  ICU 49

## ◆ getWindowsID()

static UnicodeString & icu::TimeZone::getWindowsID | ( | const UnicodeString & | id,
|  | UnicodeString & | winid,
|  | UErrorCode & | status )
| static

Converts a system time zone ID to an equivalent Windows time zone ID.

For example, Windows time zone ID "Pacific Standard Time" is returned for input "America/Los_Angeles".

There are system time zones that cannot be mapped to Windows zones. When the input system time zone ID is unknown or unmappable to a Windows time zone, then the result will be empty, but the operation itself remains successful (no error status set on return).

This implementation utilizes Zone-Tzid mapping data. The mapping data is updated time to time. To get the latest changes, please read the ICU user guide section Updating the Time Zone Data.

Parameters

  id | A system time zone ID.
  winid | Receives a Windows time zone ID. When the input system time zone ID is unknown or unmappable to a Windows time zone ID, then an empty string is set on return.
  status | Receives the status.

Returns
  A reference to the result (`winid`).

See also
  getIDForWindowsID

Stable
  ICU 52

## ◆ hasSameRules()

virtual UBool icu::TimeZone::hasSameRules | ( | const TimeZone & | other | ) | const
| virtual

Returns true if this zone has the same rule and offset as another zone.

That is, if this zone differs only in ID, if at all.

Parameters

  other | the `TimeZone` object to be compared with

Returns
  true if the given zone is the same as this one, with the possible exception of the ID

Stable
  ICU 2.0

Reimplemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ inDaylightTime()

virtual UBool icu::TimeZone::inDaylightTime | ( | UDate | date,
|  | UErrorCode & | status ) const
| pure virtual

Queries if the given date is in daylight savings time in this time zone.

This method is wasteful since it creates a new GregorianCalendar and deletes it each time it is called. This is a deprecated method and provided only for Java compatibility.

Parameters

  date | the given UDate.
  status | Output param filled in with success/error code.

Returns
  true if the given date is in daylight savings time, false, otherwise.

Deprecated
  ICU 2.4. Use Calendar::inDaylightTime() instead.

Implemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ loadRule()

static UResourceBundle * icu::TimeZone::loadRule | ( | const UResourceBundle * | top,
|  | const UnicodeString & | ruleid,
|  | UResourceBundle * | oldbundle,
|  | UErrorCode & | status )
| staticprotected

Utility function.

For internally loading rule data.

Parameters

  top | Top resource bundle for tz data
  ruleid | ID of rule to load
  oldbundle | Old bundle to reuse or nullptr
  status | Status parameter

Returns
  either a new bundle or *oldbundle

Internal
  Do not use. This API is for internal use only.

## ◆ operator!=()

bool icu::TimeZone::operator!= | ( | const TimeZone & | that | ) | const
| inline

Returns true if the two TimeZones are NOT equal; that is, if operator==() returns false.

Parameters

  that | The TimeZone object to be compared with.

Returns
  true if the given TimeZone is not equal to this TimeZone; false otherwise.

Stable
  ICU 2.0

Definition at line 550 of file timezone.h.

References icu::operator==().

## ◆ operator=()

TimeZone & icu::TimeZone::operator= | ( | const TimeZone & | right | ) |
| protected

Default assignment operator.

Parameters

  right | the object to be copied.

Stable
  ICU 2.0

## ◆ operator==()

virtual bool icu::TimeZone::operator== | ( | const TimeZone & | that | ) | const
| virtual

Returns true if the two TimeZones are equal.

(The TimeZone version only compares IDs, but subclasses are expected to also compare the fields they add.)

Parameters

  that | The TimeZone object to be compared with.

Returns
  true if the given TimeZone is equal to this TimeZone; false otherwise.

Stable
  ICU 2.0

Reimplemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ setDefault()

static void icu::TimeZone::setDefault | ( | const TimeZone & | zone | ) |
| static

Same as adoptDefault(), except that the TimeZone object passed in is NOT adopted; the caller remains responsible for deleting it.

Parameters

  zone | The given timezone.

System
  Do not use unless you know what you are doing.

Stable
  ICU 2.0

## ◆ setID()

void icu::TimeZone::setID | ( | const UnicodeString & | ID | ) |
| inline

Sets the TimeZone's ID to the specified value.

This doesn't affect any other fields (for example, if you say< blockquote>

    .     TimeZone* foo = TimeZone::createTimeZone("America/New_York");
    .     foo.setID("America/Los_Angeles");

the time zone's GMT offset and daylight-savings rules don't change to those for Los Angeles. They're still those for New York. Only the ID has changed.)

Parameters

  ID | The new time zone ID.

Stable
  ICU 2.0

Definition at line 1056 of file timezone.h.

## ◆ setRawOffset()

virtual void icu::TimeZone::setRawOffset | ( | int32_t | offsetMillis | ) |
| pure virtual

Sets the TimeZone's raw GMT offset (i.e., the number of milliseconds to add to GMT to get local time, before taking daylight savings time into account).

Parameters

  offsetMillis | The new raw GMT offset for this time zone.

Stable
  ICU 2.0

Implemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## ◆ useDaylightTime()

virtual UBool icu::TimeZone::useDaylightTime | ( |  | ) | const
| pure virtual

Queries if this time zone uses daylight savings time.

Returns
  true if this time zone uses daylight savings time, false, otherwise.

Note:The default implementation of ICU TimeZone uses the tz database, which supports historic rule changes, for system time zones. With the implementation, there are time zones that used daylight savings time in the past, but no longer used currently. For example, Asia/Tokyo has never used daylight savings time since 1951. Most clients would expect that this method to return `false` for such case. The default implementation of this method returns `true` when the time zone uses daylight savings time in the current (Gregorian) calendar year.

In Java 7, `observesDaylightTime()` was added in addition to `useDaylightTime()`. In Java, `useDaylightTime()` only checks if daylight saving time is observed by the last known rule. This specification might not be what most users would expect if daylight saving time is currently observed, but not scheduled in future. In this case, Java's `userDaylightTime()` returns `false`. To resolve the issue, Java 7 added `observesDaylightTime()`, which takes the current rule into account. The method `observesDaylightTime()` was added in ICU4J for supporting API signature compatibility with JDK. In general, ICU4C also provides JDK compatible methods, but the current implementation `userDaylightTime()` serves the purpose (takes the current rule into account), `observesDaylightTime()` is not added in ICU4C. In addition to `useDaylightTime()`, ICU4C `BasicTimeZone` class (Note that `TimeZone::createTimeZone(const UnicodeString &ID)` always returns a `BasicTimeZone`) provides a series of methods allowing historic and future time zone rule iteration, so you can check if daylight saving time is observed or not within a given period.

Stable
  ICU 2.0

Implemented in icu::RuleBasedTimeZone, icu::SimpleTimeZone, and icu::VTimeZone.

## Friends And Related Symbol Documentation

## ◆ TZEnumeration

friend class TZEnumeration
| friend

Definition at line 1040 of file timezone.h.

## ◆ ZoneMeta

friend class ZoneMeta
| friend

Definition at line 953 of file timezone.h.

The documentation for this class was generated from the following file:

- i18n/unicode/timezone.h