cppdraft_translate/cppdraft/time/zone/info.md

[time.zone.info]

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

## 30.11 Time zones [[time.zone]](time.zone#info)

### 30.11.4 Information classes [time.zone.info]

#### [30.11.4.1](#sys) Class sys_info [[time.zone.info.sys]](time.zone.info.sys)

namespace std::chrono {struct sys_info { sys_seconds begin;
 sys_seconds end;
 seconds offset;
 minutes save;
 string abbrev; };}

[1](#sys-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9243)

A sys_info object can be obtained
from the combination of a time_zone and
either a sys_time or local_time[.](#sys-1.sentence-1)

It can also be obtained from a zoned_time,
which is effectively a pair of a time_zone and sys_time[.](#sys-1.sentence-2)

[2](#sys-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9250)

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

This type provides a low-level interface to time zone information[.](#sys-2.sentence-1)

Typical conversions from sys_time to local_time will use this class implicitly, not explicitly[.](#sys-2.sentence-2)

— *end note*]

[3](#sys-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9257)

The begin and end data members indicate that,
for the associated time_zone and time_point,
the offset and abbrev are in effect in the range [begin, end)[.](#sys-3.sentence-1)

This information can be used to efficiently iterate the transitions of a time_zone[.](#sys-3.sentence-2)

[4](#sys-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9265)

The offset data member indicates
the UTC offset in effect
for the associated time_zone and time_point[.](#sys-4.sentence-1)

The relationship between local_time and sys_time is:offset = local_time - sys_time

[5](#sys-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9275)

The save data member is extra information not normally needed
for conversion between local_time and sys_time[.](#sys-5.sentence-1)

If save != 0min, this sys_info is said to be on “daylight saving” time,
and offset - save suggests what offset this time_zone might use
if it were off daylight saving time[.](#sys-5.sentence-2)

However, this information should not be taken as authoritative[.](#sys-5.sentence-3)

The only sure way to get such information
is to query the time_zone with a time_point that returns a sys_info where save == 0min[.](#sys-5.sentence-4)

There is no guarantee what time_point might return such a sys_info except that it is guaranteed not to be in the range [begin, end)
(if save != 0min for this sys_info)[.](#sys-5.sentence-5)

[6](#sys-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9290)

The abbrev data member indicates
the current abbreviation used for the associated time_zone and time_point[.](#sys-6.sentence-1)

Abbreviations are not unique among the time_zones,
and so one cannot reliably map abbreviations back to a time_zone and UTC offset[.](#sys-6.sentence-2)

[🔗](#lib:operator%3c%3c,sys_info)

`template<class charT, class traits>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const sys_info& r);
`

[7](#sys-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9305)

*Effects*: Streams out the sys_info object r in an unspecified format[.](#sys-7.sentence-1)

[8](#sys-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9309)

*Returns*: os[.](#sys-8.sentence-1)

#### [30.11.4.2](#local) Class local_info [[time.zone.info.local]](time.zone.info.local)

[🔗](#lib:unique,local_info)

namespace std::chrono {struct local_info {static constexpr int unique = 0; static constexpr int nonexistent = 1; static constexpr int ambiguous = 2; int result;
 sys_info first;
 sys_info second; };}

[1](#local-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9337)

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

This type provides a low-level interface to time zone information[.](#local-1.sentence-1)

Typical conversions from local_time to sys_time will use this class implicitly, not explicitly[.](#local-1.sentence-2)

— *end note*]

[2](#local-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9344)

Describes the result of converting a local_time to a sys_time as follows:

- [(2.1)](#local-2.1)

  When a local_time to sys_time conversion is unique,result == unique,first will be filled out with the correct sys_info,
andsecond will be zero-initialized[.](#local-2.1.sentence-1)

- [(2.2)](#local-2.2)

  If the conversion stems from a nonexistent local_time then result == nonexistent,first will be filled out with the sys_info that ends just prior to the local_time,
andsecond will be filled out with the sys_info that begins just after the local_time[.](#local-2.2.sentence-1)

- [(2.3)](#local-2.3)

  If the conversion stems from an ambiguous local_time,
then result == ambiguous,first will be filled out with the sys_info that ends just after the local_time,
andsecond will be filled out with the sys_info that starts just before the local_time[.](#local-2.3.sentence-1)

[🔗](#lib:operator%3c%3c,local_info)

`template<class charT, class traits>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const local_info& r);
`

[3](#local-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9382)

*Effects*: Streams out the local_info object r in an unspecified format[.](#local-3.sentence-1)

[4](#local-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L9386)

*Returns*: os[.](#local-4.sentence-1)