QTimeZone Class▲

  • Header: QTimeZone

  • Since: Qt 5.2

  • CMake:

    find_package(Qt6 REQUIRED COMPONENTS Core)

    target_link_libraries(mytarget PRIVATE Qt6::Core)

  • qmake: QT += core

Detailed Description▲

This class provides a stateless calculator for time zone conversions between UTC and the local time in a specific time zone. By default it uses the host system time zone data to perform these conversions.

This class is primarily designed for use in QDateTime; most applications will not need to access this class directly and should instead use QDateTime with a Qt::TimeSpec of Qt::TimeZone.

For consistency with QDateTime, QTimeZone does not account for leap seconds.

Remarks▲

 
IANA Time Zone IDs▲

QTimeZone uses the IANA time zone IDs as defined in the IANA Time Zone Database (http://www.iana.org/time-zones). This is to ensure a standard ID across all supported platforms. Most platforms support the IANA IDs and the IANA Database natively, but for Windows a mapping is required to the native IDs. See below for more details.

The IANA IDs can and do change on a regular basis, and can vary depending on how recently the host system data was updated. As such you cannot rely on any given ID existing on any host system. You must use availableTimeZoneIds() to determine what IANA IDs are available.

The IANA IDs and database are also know as the Olson IDs and database, named after their creator.

UTC Offset Time Zones▲

A default UTC time zone backend is provided which is always guaranteed to be available. This provides a set of generic Offset From UTC time zones in the range UTC-14:00 to UTC+14:00. These time zones can be created using either the standard ISO format names "UTC+00:00" as listed by availableTimeZoneIds(), or using the number of offset seconds.

Windows Time Zones▲

Windows native time zone support is severely limited compared to the standard IANA TZ Database. Windows time zones cover larger geographic areas and are thus less accurate in their conversions. They also do not support as much historical data and so may only be accurate for the current year. In particular, when MS's zone data claims that DST was observed prior to 1900 (this is historically known to be untrue), the claim is ignored and the standard time (allegedly) in force in 1900 is taken to have always been in effect.

QTimeZone uses a conversion table derived from the Unicode CLDR data to map between IANA IDs and Windows IDs. Depending on your version of Windows and Qt, this table may not be able to provide a valid conversion, in which "UTC" will be returned.

QTimeZone provides a public API to use this conversion table. The Windows ID used is the Windows Registry Key for the time zone which is also the MS Exchange EWS ID as well, but is different to the Time Zone Name (TZID) and COD code used by MS Exchange in versions before 2007.

System Time Zone▲