29 Time library [time]

29.11 Time zones [time.zone]

29.11.2 Time zone database [time.zone.db]

29.11.2.4 Remote time zone database support [time.zone.db.remote]

1
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The local time zone database is that supplied by the implementation when the program first accesses the database, for example via current_zone().
While the program is running, the implementation may choose to update the time zone database.
This update shall not impact the program in any way unless the program calls the functions in this subclause.
This potentially updated time zone database is referred to as the remote time zone database.
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const tzdb& reload_tzdb();
2
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Effects: This function first checks the version of the remote time zone database.
If the versions of the local and remote databases are the same, there are no effects.
Otherwise the remote database is pushed to the front of the tzdb_list accessed by get_tzdb_list().
3
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Synchronization: This function is thread-safe with respect to get_tzdb_list().front() and get_tzdb_list().erase_after().
4
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Postconditions: No pointers, references, or iterators are invalidated.
5
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Returns: get_tzdb_list().front().
6
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Throws: runtime_error if for any reason a reference cannot be returned to a valid tzdb.
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string remote_version();
7
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Returns: The latest remote database version.
[Note 1: 
This can be compared with get_tzdb().version to discover if the local and remote databases are equivalent.
— end note]