tmp/tmpv5b_fe10/{from.md → to.md}
RENAMED
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###
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system-wide realtime clock.
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``` cpp
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class system_clock {
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public:
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using rep = see below;
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using period = ratio<unspecified, unspecified{}>;
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using duration = chrono::duration<rep, period>;
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using time_point = chrono::time_point<system_clock>;
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static constexpr bool is_steady = unspecified;
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static time_point now() noexcept;
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static time_t to_time_t (const time_point& t) noexcept;
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static time_point from_time_t(time_t t) noexcept;
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};
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```
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``` cpp
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using system_clock::rep = unspecified;
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```
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*
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`system_clock::duration::min() < system_clock::duration::zero()`
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[*Note 1*: This implies that `rep` is a signed type. — *end note*]
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``` cpp
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static time_t to_time_t(const time_point& t) noexcept;
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@@ -46,5 +61,65 @@ static time_point from_time_t(time_t t) noexcept;
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*Returns:* A `time_point` object that represents the same point in time
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as `t` when both values are restricted to the coarser of the precisions
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of `time_t` and `time_point`. It is *implementation-defined* whether
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values are rounded or truncated to the required precision.
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### Class `system_clock` <a id="time.clock.system">[[time.clock.system]]</a>
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#### Overview <a id="time.clock.system.overview">[[time.clock.system.overview]]</a>
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``` cpp
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namespace std::chrono {
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class system_clock {
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public:
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using rep = see below;
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using period = ratio<unspecified, unspecified{}>;
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using duration = chrono::duration<rep, period>;
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using time_point = chrono::time_point<system_clock>;
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static constexpr bool is_steady = unspecified;
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static time_point now() noexcept;
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// mapping to/from C type time_t
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static time_t to_time_t (const time_point& t) noexcept;
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static time_point from_time_t(time_t t) noexcept;
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};
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}
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```
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Objects of type `system_clock` represent wall clock time from the
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system-wide realtime clock. Objects of type `sys_time<Duration>` measure
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time since 1970-01-01 00:00:00 UTC excluding leap seconds. This measure
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is commonly referred to as *Unix time*. This measure facilitates an
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efficient mapping between `sys_time` and calendar types [[time.cal]].
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[*Example 1*:
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`sys_seconds{sys_days{1970y/January/1}}.time_since_epoch()` is `0s`.
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`sys_seconds{sys_days{2000y/January/1}}.time_since_epoch()` is
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`946'684'800s`, which is `10'957 * 86'400s`.
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— *end example*]
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#### Members <a id="time.clock.system.members">[[time.clock.system.members]]</a>
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``` cpp
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using system_clock::rep = unspecified;
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```
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*Constraints:*
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`system_clock::duration::min() < system_clock::duration::zero()` is
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`true`.
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[*Note 1*: This implies that `rep` is a signed type. — *end note*]
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``` cpp
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static time_t to_time_t(const time_point& t) noexcept;
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*Returns:* A `time_point` object that represents the same point in time
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as `t` when both values are restricted to the coarser of the precisions
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of `time_t` and `time_point`. It is *implementation-defined* whether
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values are rounded or truncated to the required precision.
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#### Non-member functions <a id="time.clock.system.nonmembers">[[time.clock.system.nonmembers]]</a>
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``` cpp
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template<class charT, class traits, class Duration>
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basic_ostream<charT, traits>&
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operator<<(basic_ostream<charT, traits>& os, const sys_time<Duration>& tp);
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```
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*Constraints:* `treat_as_floating_point_v<typename Duration::rep>` is
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`false`, and `Duration{1} < days{1}` is `true`.
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*Effects:* Equivalent to:
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``` cpp
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auto const dp = floor<days>(tp);
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return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{} {}"),
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year_month_day{dp}, hh_mm_ss{tp-dp});
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```
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[*Example 1*:
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``` cpp
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cout << sys_seconds{0s} << '\n'; // 1970-01-01 00:00:00
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cout << sys_seconds{946'684'800s} << '\n'; // 2000-01-01 00:00:00
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cout << sys_seconds{946'688'523s} << '\n'; // 2000-01-01 01:02:03
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```
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— *end example*]
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``` cpp
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template<class charT, class traits>
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basic_ostream<charT, traits>&
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operator<<(basic_ostream<charT, traits>& os, const sys_days& dp);
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```
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*Effects:* `os << year_month_day{dp}`.
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*Returns:* `os`.
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``` cpp
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template<class charT, class traits, class Duration, class Alloc = allocator<charT>>
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basic_istream<charT, traits>&
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from_stream(basic_istream<charT, traits>& is, const charT* fmt,
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sys_time<Duration>& tp, basic_string<charT, traits, Alloc>* abbrev = nullptr,
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minutes* offset = nullptr);
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```
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*Effects:* Attempts to parse the input stream `is` into the `sys_time`
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`tp` using the format flags given in the NTCTS `fmt` as specified in
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[[time.parse]]. If the parse fails to decode a valid date,
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`is.setstate(ios_base::failbit)` is called and `tp` is not modified. If
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`%Z` is used and successfully parsed, that value will be assigned to
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`*abbrev` if `abbrev` is non-null. If `%z` (or a modified variant) is
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used and successfully parsed, that value will be assigned to `*offset`
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if `offset` is non-null. Additionally, the parsed offset will be
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subtracted from the successfully parsed timestamp prior to assigning
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that difference to `tp`.
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*Returns:* `is`.
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