class TimeZone
Defined at line 133 of file ../../third_party/icu/default/source/i18n/unicode/timezone.h
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.)
<P
>
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.
<P
>
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().
<P
>
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").
Public Methods
bool operator!= (const TimeZone & that)Returns true if the two TimeZones are NOT equal; that is, if operator==() returns
false.
Parameters
Returns
true if the given TimeZone is not equal to this TimeZone; false
otherwise.
ICU 2.0
Defined at line 550 of file ../../third_party/icu/default/source/i18n/unicode/timezone.h
void ~TimeZone ()ICU 2.0
const TimeZone & getUnknown ()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.
const TimeZone * getGMT ()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.
TimeZone * createTimeZone (const UnicodeString & ID)Creates a
TimeZone
for the given ID.
Parameters
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.
ICU 2.0
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.
Parameters
Returns
an enumeration object, owned by the caller.
ICU 4.8
StringEnumeration * createEnumeration ()Returns an enumeration over all recognized time zone IDs. (i.e.,
all strings that createTimeZone() accepts)
Returns
an enumeration object, owned by the caller.
StringEnumeration * createEnumeration (UErrorCode & status)Returns an enumeration over all recognized time zone IDs. (i.e.,
all strings that createTimeZone() accepts)
Parameters
Returns
an enumeration object, owned by the caller.
ICU 70
StringEnumeration * createEnumeration (int32_t rawOffset)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
Returns
an enumeration object, owned by the caller
StringEnumeration * createEnumerationForRawOffset (int32_t rawOffset, UErrorCode & status)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
Returns
an enumeration object, owned by the caller
ICU 70
StringEnumeration * createEnumeration (const char * region)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
Returns
an enumeration object, owned by the caller
StringEnumeration * createEnumerationForRegion (const char * region, UErrorCode & status)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
Returns
an enumeration object, owned by the caller
ICU 70
int32_t countEquivalentIDs (const UnicodeString & id)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
Returns
the number of zones in the equivalency group containing
'id', or zero if 'id' is not a valid system ID
UnicodeString getEquivalentID (const UnicodeString & id, int32_t index)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
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
TimeZone * detectHostTimeZone ()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.
TimeZone * createDefault ()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.
TimeZone * forLocaleOrDefault (const Locale & locale)If the locale contains the timezone keyword, creates a copy of that TimeZone.
Otherwise, create the default timezone.
Parameters
Returns
A TimeZone. Clients are responsible for deleting the time zone
object returned.
void adoptDefault (TimeZone * zone)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
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.
Parameters
const char * getTZDataVersion (UErrorCode & status)Returns the timezone data version currently used by ICU.
Parameters
Returns
the version string, such as "2007f"
ICU 3.8
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.
Parameters
Returns
A reference to the result.
ICU 4.0
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.
Parameters
Returns
A reference to the result.
ICU 4.0
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.
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
Returns
A reference to the result.
ICU 74
UnicodeString & getWindowsID (const UnicodeString & id, UnicodeString & winid, UErrorCode & status)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
.
ICU 52
Parameters
Returns
A reference to the result (
winid
).
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. 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
.
ICU 52
Parameters
Returns
A reference to the result (
id
).
bool operator== (const TimeZone & that)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
Returns
true if the given TimeZone is equal to this TimeZone; false
otherwise.
ICU 2.0
int32_t getOffset (uint8_t era, int32_t year, int32_t month, int32_t day, uint8_t dayOfWeek, int32_t millis, UErrorCode & status)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
Returns
The offset in milliseconds to add to GMT to get local time.
ICU 2.0
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)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
Returns
the offset to add *to* GMT to get local time.
ICU 2.0
void getOffset (UDate date, UBool local, int32_t & rawOffset, int32_t & dstOffset, UErrorCode & ec)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().
ICU 2.8
Parameters
void setRawOffset (int32_t offsetMillis)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
int32_t getRawOffset ()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.
ICU 2.0
UnicodeString & getID (UnicodeString & ID)-------------------------------------
Defined at line 1046 of file ../../third_party/icu/default/source/i18n/unicode/timezone.h
void setID (const UnicodeString & ID)-------------------------------------
Defined at line 1055 of file ../../third_party/icu/default/source/i18n/unicode/timezone.h
UnicodeString & getDisplayName (UnicodeString & result)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
Returns
A reference to 'result'.
ICU 2.0
UnicodeString & getDisplayName (const Locale & locale, UnicodeString & result)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
Returns
A reference to 'result'.
ICU 2.0
UnicodeString & getDisplayName (UBool inDaylight, EDisplayType style, UnicodeString & result)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
Returns
A reference to 'result'.
ICU 2.0
UnicodeString & getDisplayName (UBool inDaylight, EDisplayType style, const Locale & locale, UnicodeString & result)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
Returns
A reference to 'result'.
ICU 2.0
UBool useDaylightTime ()Queries if this time zone uses daylight savings time.
ICU 2.0
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.
UBool inDaylightTime (UDate date, UErrorCode & status)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
Returns
true if the given date is in daylight savings time,
false, otherwise.
UBool hasSameRules (const TimeZone & other)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
Returns
true if the given zone is the same as this one,
with the possible exception of the ID
ICU 2.0
TimeZone * clone ()Clones TimeZone objects polymorphically. Clients are responsible for deleting
the TimeZone object cloned.
Returns
A new copy of this TimeZone object.
ICU 2.0
UClassID getStaticClassID ()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.
ICU 2.0
UClassID getDynamicClassID ()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.
<P
>
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.
ICU 2.0
int32_t getDSTSavings ()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
ICU 3.6
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. 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
Returns
The length of the output region code.
ICU 4.8
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.
Parameters
Returns
the region associated with the given zone
Protected Methods
void TimeZone ()Default constructor. ID is initialized to the empty string.
ICU 2.0
void TimeZone (const UnicodeString & id)Construct a TimeZone with a given ID.
Parameters
void TimeZone (const TimeZone & source)Copy constructor.
Parameters
TimeZone & operator= (const TimeZone & right)Default assignment operator.
Parameters
UResourceBundle * loadRule (const UResourceBundle * top, const UnicodeString & ruleid, UResourceBundle * oldbundle, UErrorCode & status)Utility function. For internally loading rule data.
Parameters
Returns
either a new bundle or *oldbundle
Enumerations
enum EDisplayType| Name | Value |
|---|---|
| SHORT | 1 |
| LONG | 2 |
| SHORT_GENERIC | 3 |
| LONG_GENERIC | 4 |
| SHORT_GMT | 5 |
| LONG_GMT | 6 |
| SHORT_COMMONLY_USED | 7 |
| GENERIC_LOCATION | 8 |
Enum for use with getDisplayName
ICU 2.4
Defined at line 675 of file ../../third_party/icu/default/source/i18n/unicode/timezone.h
Friends
class TZEnumerationclass ZoneMeta