The twentieth century is now some way behind us, so using its years when parsing a date-time format that only provides the last two digits is increasingly likely to produce unwelcome results. Most such formats are saved by the "redundant" presence of a day-of-week field but, for those that are not (notably including ASN.1 date fields), there is a need to provide some way to over-ride the twentieth century default. Allow the caller to pass a base year to the fromString() methods, of QDate and QDateTime, and to QLocale's toDate() and toDateTime(), that indicates the first of 100 consecutive years, among which the two digits given can select a year. Add some test-cases to exercise the new API. [ChangeLog][QtCore][QDate] When fromString() has only a two-digit year to go on, it is now possible to set the start-year of the century within which this selects. [ChangeLog][QtCore][QDateTime] When fromString() has only a two-digit year to go on, it is now possible to set the start-year of the century within which this selects. [ChangeLog][QtCore][QLocale] When toDate() or toDateTime() has only a two-digit year to go on, it is now possible to set the start-year of the century within which this selects. Fixes: QTBUG-46843 Change-Id: Ieb312ee9e0b80557a15edcb0e6d75a57b10d7a62 Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org> Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>