[time.zone.db.remote]

# 30 Time library [[time]](./#time)

## 30.11 Time zones [[time.zone]](time.zone#db.remote)

### 30.11.2 Time zone database [[time.zone.db]](time.zone.db#remote)

#### 30.11.2.4 Remote time zone database support [time.zone.db.remote]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9018)

The local time zone database
is that supplied by the implementation
when the program first accesses the database,
for example via current_zone()[.](#1.sentence-1)

While the program is running,
the implementation may choose to update the time zone database[.](#1.sentence-2)

This update shall not impact the program in any way
unless the program calls the functions in this subclause[.](#1.sentence-3)

This potentially updated time zone database
is referred to as the [*remote time zone database*](#def:remote_time_zone_database "30.11.2.4 Remote time zone database support [time.zone.db.remote]")[.](#1.sentence-4)

[🔗](#lib:reload_tzdb)

`const tzdb& reload_tzdb();
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9036)

*Effects*: This function first checks
the version of the remote time zone database[.](#2.sentence-1)

If the versions of the local and remote databases are the same,
there are no effects[.](#2.sentence-2)

Otherwise the remote database is pushed
to the front of the tzdb_list accessed by get_tzdb_list()[.](#2.sentence-3)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9046)

*Synchronization*: This function is thread-safe with respect toget_tzdb_list().front() and get_tzdb_list().erase_after()[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9051)

*Postconditions*: No pointers, references, or iterators are invalidated[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9055)

*Returns*: get_tzdb_list().front()[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9059)

*Throws*: runtime_error if for any reason
a reference cannot be returned to a valid tzdb[.](#6.sentence-1)

[🔗](#lib:remote_version)

`string remote_version();
`

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9071)

*Returns*: The latest remote database version[.](#7.sentence-1)

[*Note [1](#note-1)*:

This can be compared with get_tzdb().version to discover if the local and remote databases are equivalent[.](#7.sentence-2)

— *end note*]