tmp/tmpgkt2u96i/{from.md → to.md}
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| 1 |
+
### Information classes <a id="time.zone.info">[[time.zone.info]]</a>
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| 2 |
+
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| 3 |
+
#### Class `sys_info` <a id="time.zone.info.sys">[[time.zone.info.sys]]</a>
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| 4 |
+
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| 5 |
+
``` cpp
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+
namespace std::chrono {
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struct sys_info {
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| 8 |
+
sys_seconds begin;
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| 9 |
+
sys_seconds end;
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| 10 |
+
seconds offset;
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| 11 |
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minutes save;
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| 12 |
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string abbrev;
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| 13 |
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};
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}
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```
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| 16 |
+
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+
A `sys_info` object can be obtained from the combination of a
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| 18 |
+
`time_zone` and either a `sys_time` or `local_time`. It can also be
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| 19 |
+
obtained from a `zoned_time`, which is effectively a pair of a
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| 20 |
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`time_zone` and `sys_time`.
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| 21 |
+
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| 22 |
+
[*Note 1*: This type provides a low-level interface to time zone
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| 23 |
+
information. Typical conversions from `sys_time` to `local_time` will
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| 24 |
+
use this class implicitly, not explicitly. — *end note*]
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| 25 |
+
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| 26 |
+
The `begin` and `end` data members indicate that, for the associated
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| 27 |
+
`time_zone` and `time_point`, the `offset` and `abbrev` are in effect in
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| 28 |
+
the range \[`begin`, `end`). This information can be used to efficiently
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| 29 |
+
iterate the transitions of a `time_zone`.
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| 30 |
+
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| 31 |
+
The `offset` data member indicates the UTC offset in effect for the
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| 32 |
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associated `time_zone` and `time_point`. The relationship between
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| 33 |
+
`local_time` and `sys_time` is:
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| 34 |
+
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| 35 |
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``` cpp
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| 36 |
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offset = local_time - sys_time
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| 37 |
+
```
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| 38 |
+
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| 39 |
+
The `save` data member is extra information not normally needed for
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| 40 |
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conversion between `local_time` and `sys_time`. If `save != 0min`, this
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| 41 |
+
`sys_info` is said to be on “daylight saving” time, and `offset - save`
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| 42 |
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suggests what offset this `time_zone` might use if it were off daylight
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| 43 |
+
saving time. However, this information should not be taken as
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| 44 |
+
authoritative. The only sure way to get such information is to query the
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| 45 |
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`time_zone` with a `time_point` that returns a `sys_info` where
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| 46 |
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`save == 0min`. There is no guarantee what `time_point` might return
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| 47 |
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such a `sys_info` except that it is guaranteed not to be in the range
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| 48 |
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\[`begin`, `end`) (if `save != 0min` for this `sys_info`).
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| 49 |
+
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| 50 |
+
The `abbrev` data member indicates the current abbreviation used for the
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| 51 |
+
associated `time_zone` and `time_point`. Abbreviations are not unique
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| 52 |
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among the `time_zones`, and so one cannot reliably map abbreviations
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| 53 |
+
back to a `time_zone` and UTC offset.
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| 54 |
+
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| 55 |
+
``` cpp
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| 56 |
+
template<class charT, class traits>
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| 57 |
+
basic_ostream<charT, traits>&
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| 58 |
+
operator<<(basic_ostream<charT, traits>& os, const sys_info& r);
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| 59 |
+
```
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| 60 |
+
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| 61 |
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*Effects:* Streams out the `sys_info` object `r` in an unspecified
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| 62 |
+
format.
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| 63 |
+
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| 64 |
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*Returns:* `os`.
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| 65 |
+
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| 66 |
+
#### Class `local_info` <a id="time.zone.info.local">[[time.zone.info.local]]</a>
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| 67 |
+
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| 68 |
+
``` cpp
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| 69 |
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namespace std::chrono {
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| 70 |
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struct local_info {
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| 71 |
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static constexpr int unique = 0;
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| 72 |
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static constexpr int nonexistent = 1;
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| 73 |
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static constexpr int ambiguous = 2;
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| 74 |
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| 75 |
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int result;
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| 76 |
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sys_info first;
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| 77 |
+
sys_info second;
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| 78 |
+
};
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| 79 |
+
}
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| 80 |
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```
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| 81 |
+
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| 82 |
+
[*Note 1*: This type provides a low-level interface to time zone
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| 83 |
+
information. Typical conversions from `local_time` to `sys_time` will
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| 84 |
+
use this class implicitly, not explicitly. — *end note*]
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| 85 |
+
|
| 86 |
+
Describes the result of converting a `local_time` to a `sys_time` as
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| 87 |
+
follows:
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| 88 |
+
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| 89 |
+
- When a `local_time` to `sys_time` conversion is unique,
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| 90 |
+
`result == unique`, `first` will be filled out with the correct
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| 91 |
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`sys_info`, and `second` will be zero-initialized.
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| 92 |
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- If the conversion stems from a nonexistent `local_time` then
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| 93 |
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`result == nonexistent`, `first` will be filled out with the
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| 94 |
+
`sys_info` that ends just prior to the `local_time`, and `second` will
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| 95 |
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be filled out with the `sys_info` that begins just after the
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| 96 |
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`local_time`.
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| 97 |
+
- If the conversion stems from an ambiguous `local_time`, then
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| 98 |
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`result == ambiguous`, `first` will be filled out with the `sys_info`
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| 99 |
+
that ends just after the `local_time`, and `second` will be filled out
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| 100 |
+
with the `sys_info` that starts just before the `local_time`.
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| 101 |
+
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| 102 |
+
``` cpp
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| 103 |
+
template<class charT, class traits>
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| 104 |
+
basic_ostream<charT, traits>&
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| 105 |
+
operator<<(basic_ostream<charT, traits>& os, const local_info& r);
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| 106 |
+
```
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| 107 |
+
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| 108 |
+
*Effects:* Streams out the `local_info` object `r` in an unspecified
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| 109 |
+
format.
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| 110 |
+
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| 111 |
+
*Returns:* `os`.
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| 112 |
+
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