These functions provide access to the program-wide time zone database.

1) Returns a reference to the global std::chrono::tzdb_list singleton. If this is the first access to the database, initialize the database. After the initialization, the database will hold a single initialized std::chrono::tzdb object. This function is thread-safe: concurrent calls to this function from multiple threads do not introduce a data race.

2) Returns a reference to the first std::chrono::tzdb object held by the tzdb_list singleton. Equivalent to std::chrono::get_tzdb_list().front().

3) Returns a string containing the latest remote database version.

4) If remote_version() != get_tzdb().version, pushes a new tzdb object representing the remote database to the front of the tzdb_list singleton referenced by get_tzdb_list(). Otherwise there are no effects. No references, pointers or iterators are invalidated. Calling this function concurrently with get_tzdb_list().front() or get_tzdb_list().erase_after() does not introduce a data race.

Exceptions

1) std::runtime_error if for any reason a reference to a tzdb_list containing one or more valid tzdb cannot be returned.

Return value

1) A reference to the global std::chrono::tzdb_list singleton.

2) std::chrono::get_tzdb_list().front().

3) A string containing the latest remote database version.

4) std::chrono::get_tzdb_list().front() (after any update made by this function).