\rSec0[time]{Time library}

\rSec1[time.general]{General}

\indexlibraryglobal{chrono}%

This Clause describes the chrono library\iref{time.syn} and various C

functions\iref{ctime.syn} that provide generally useful time

utilities, as summarized in \tref{time.summary}.

\begin{libsumtab}{Time library summary}{time.summary}

\ref{time.clock.req} & \oldconcept{Clock} requirements & \\ \rowsep

\ref{time.traits} & Time-related traits & \tcode{<chrono>} \\

\ref{time.duration} & Class template \tcode{duration} & \\

\ref{time.point} & Class template \tcode{time_point} & \\

\ref{time.clock} & Clocks & \\

\ref{time.cal} & Civil calendar & \\

\ref{time.hms} & Class template \tcode{hh_mm_ss} & \\

\ref{time.12} & 12/24 hour functions & \\

\ref{time.zone} & Time zones & \\

\ref{time.format} & Formatting & \\

\ref{time.parse} & Parsing & \\

\ref{time.hash} & Hash support & \\ \rowsep

\ref{ctime.syn} & C library time utilities & \tcode{<ctime>} \\

\end{libsumtab}

\indextext{STATICALLY-WIDEN@\exposid{STATICALLY-WIDEN}}%

Let \exposid{STATICALLY-WIDEN}\tcode{<charT>("...")} be

\tcode{"..."} if \tcode{charT} is \tcode{char} and

\tcode{L"..."} if \tcode{charT} is \keyword{wchar_t}.

\rSec1[time.syn]{Header \tcode{<chrono>} synopsis}

\indexheader{chrono}%

\indexlibraryglobal{treat_as_floating_point_v}%

\indexlibraryglobal{is_clock_v}%

\indexlibraryglobal{nanoseconds}%

\indexlibraryglobal{microseconds}%

\indexlibraryglobal{milliseconds}%

\indexlibraryglobal{seconds}%

\indexlibraryglobal{minutes}%

\indexlibraryglobal{hours}%

\indexlibraryglobal{days}%

\indexlibraryglobal{weeks}%

\indexlibraryglobal{years}%

\indexlibraryglobal{months}%

\indexlibraryglobal{sys_time}%

\indexlibraryglobal{sys_seconds}%

\indexlibraryglobal{sys_days}%

\indexlibraryglobal{utc_time}%

\indexlibraryglobal{utc_seconds}%

\indexlibraryglobal{tai_time}%

\indexlibraryglobal{tai_seconds}%

\indexlibraryglobal{gps_time}%

\indexlibraryglobal{gps_seconds}%

\indexlibraryglobal{file_time}%

\indexlibraryglobal{local_time}%

\indexlibraryglobal{local_seconds}%

\indexlibraryglobal{local_days}%

\indexlibraryglobal{local_t}%

\indexlibraryglobal{choose}%

\indexlibrarymember{earliest}{choose}%

\indexlibrarymember{latest}{choose}%

\begin{codeblock}

#include <compare> // see \ref{compare.syn}

namespace std::chrono {

// \ref{time.duration}, class template \tcode{duration}

template<class Rep, class Period = ratio<1>> class duration;

// \ref{time.point}, class template \tcode{time_point}

template<class Clock, class Duration = typename Clock::duration> class time_point;

}

namespace std {

// \ref{time.traits.specializations}, \tcode{common_type} specializations

template<class Rep1, class Period1, class Rep2, class Period2>

struct common_type<chrono::duration<Rep1, Period1>,

chrono::duration<Rep2, Period2>>;

template<class Clock, class Duration1, class Duration2>

struct common_type<chrono::time_point<Clock, Duration1>,

chrono::time_point<Clock, Duration2>>;

}

namespace std::chrono {

// \ref{time.traits}, customization traits

template<class Rep> struct treat_as_floating_point;

template<class Rep>

constexpr bool treat_as_floating_point_v = treat_as_floating_point<Rep>::value;

template<class Rep> struct duration_values;

template<class T> struct is_clock;

template<class T> constexpr bool is_clock_v = is_clock<T>::value;

// \ref{time.duration.nonmember}, \tcode{duration} arithmetic

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>

operator+(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>

operator-(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period, class Rep2>

constexpr duration<common_type_t<Rep1, Rep2>, Period>

operator*(const duration<Rep1, Period>& d, const Rep2& s);

template<class Rep1, class Rep2, class Period>

constexpr duration<common_type_t<Rep1, Rep2>, Period>

operator*(const Rep1& s, const duration<Rep2, Period>& d);

template<class Rep1, class Period, class Rep2>

constexpr duration<common_type_t<Rep1, Rep2>, Period>

operator/(const duration<Rep1, Period>& d, const Rep2& s);

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr common_type_t<Rep1, Rep2>

operator/(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period, class Rep2>

constexpr duration<common_type_t<Rep1, Rep2>, Period>

operator%(const duration<Rep1, Period>& d, const Rep2& s);

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>

operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);

// \ref{time.duration.comparisons}, \tcode{duration} comparisons

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr bool operator==(const duration<Rep1, Period1>& lhs,

const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr bool operator< (const duration<Rep1, Period1>& lhs,

const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr bool operator> (const duration<Rep1, Period1>& lhs,

const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr bool operator<=(const duration<Rep1, Period1>& lhs,

const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period1, class Rep2, class Period2>

constexpr bool operator>=(const duration<Rep1, Period1>& lhs,

const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period1, class Rep2, class Period2>

requires @\seebelow@

constexpr auto operator<=>(const duration<Rep1, Period1>& lhs,

const duration<Rep2, Period2>& rhs);

// \ref{time.duration.cast}, conversions

template<class ToDuration, class Rep, class Period>

constexpr ToDuration duration_cast(const duration<Rep, Period>& d);

template<class ToDuration, class Rep, class Period>

constexpr ToDuration floor(const duration<Rep, Period>& d);

template<class ToDuration, class Rep, class Period>

constexpr ToDuration ceil(const duration<Rep, Period>& d);

template<class ToDuration, class Rep, class Period>

constexpr ToDuration round(const duration<Rep, Period>& d);

// \ref{time.duration.io}, \tcode{duration} I/O

template<class charT, class traits, class Rep, class Period>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os,

const duration<Rep, Period>& d);

template<class charT, class traits, class Rep, class Period, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

duration<Rep, Period>& d,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// convenience typedefs

using nanoseconds = duration<@\term{signed integer type of at least 64 bits}@, nano>;

using microseconds = duration<@\term{signed integer type of at least 55 bits}@, micro>;

using milliseconds = duration<@\term{signed integer type of at least 45 bits}@, milli>;

using seconds = duration<@\term{signed integer type of at least 35 bits}@>;

using minutes = duration<@\term{signed integer type of at least 29 bits}@, ratio< 60>>;

using hours = duration<@\term{signed integer type of at least 23 bits}@, ratio<3600>>;

using days = duration<@\term{signed integer type of at least 25 bits}@,

ratio_multiply<ratio<24>, hours::period>>;

using weeks = duration<@\term{signed integer type of at least 22 bits}@,

ratio_multiply<ratio<7>, days::period>>;

using years = duration<@\term{signed integer type of at least 17 bits}@,

ratio_multiply<ratio<146097, 400>, days::period>>;

using months = duration<@\term{signed integer type of at least 20 bits}@,

ratio_divide<years::period, ratio<12>>>;

// \ref{time.point.nonmember}, \tcode{time_point} arithmetic

template<class Clock, class Duration1, class Rep2, class Period2>

constexpr time_point<Clock, common_type_t<Duration1, duration<Rep2, Period2>>>

operator+(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);

template<class Rep1, class Period1, class Clock, class Duration2>

constexpr time_point<Clock, common_type_t<duration<Rep1, Period1>, Duration2>>

operator+(const duration<Rep1, Period1>& lhs, const time_point<Clock, Duration2>& rhs);

template<class Clock, class Duration1, class Rep2, class Period2>

constexpr time_point<Clock, common_type_t<Duration1, duration<Rep2, Period2>>>

operator-(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);

template<class Clock, class Duration1, class Duration2>

constexpr common_type_t<Duration1, Duration2>

operator-(const time_point<Clock, Duration1>& lhs,

const time_point<Clock, Duration2>& rhs);

// \ref{time.point.comparisons}, \tcode{time_point} comparisons

template<class Clock, class Duration1, class Duration2>

constexpr bool operator==(const time_point<Clock, Duration1>& lhs,

const time_point<Clock, Duration2>& rhs);

template<class Clock, class Duration1, class Duration2>

constexpr bool operator< (const time_point<Clock, Duration1>& lhs,

const time_point<Clock, Duration2>& rhs);

template<class Clock, class Duration1, class Duration2>

constexpr bool operator> (const time_point<Clock, Duration1>& lhs,

const time_point<Clock, Duration2>& rhs);

template<class Clock, class Duration1, class Duration2>

constexpr bool operator<=(const time_point<Clock, Duration1>& lhs,

const time_point<Clock, Duration2>& rhs);

template<class Clock, class Duration1, class Duration2>

constexpr bool operator>=(const time_point<Clock, Duration1>& lhs,

const time_point<Clock, Duration2>& rhs);

template<class Clock, class Duration1, @\libconcept{three_way_comparable_with}@<Duration1> Duration2>

constexpr auto operator<=>(const time_point<Clock, Duration1>& lhs,

const time_point<Clock, Duration2>& rhs);

// \ref{time.point.cast}, conversions

template<class ToDuration, class Clock, class Duration>

constexpr time_point<Clock, ToDuration>

time_point_cast(const time_point<Clock, Duration>& t);

template<class ToDuration, class Clock, class Duration>

constexpr time_point<Clock, ToDuration> floor(const time_point<Clock, Duration>& tp);

template<class ToDuration, class Clock, class Duration>

constexpr time_point<Clock, ToDuration> ceil(const time_point<Clock, Duration>& tp);

template<class ToDuration, class Clock, class Duration>

constexpr time_point<Clock, ToDuration> round(const time_point<Clock, Duration>& tp);

// \ref{time.duration.alg}, specialized algorithms

template<class Rep, class Period>

constexpr duration<Rep, Period> abs(duration<Rep, Period> d);

// \ref{time.clock.system}, class \tcode{system_clock}

class system_clock;

template<class Duration>

using sys_time = time_point<system_clock, Duration>;

using sys_seconds = sys_time<seconds>;

using sys_days = sys_time<days>;

template<class charT, class traits, class Duration>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const sys_time<Duration>& tp);

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const sys_days& dp);

template<class charT, class traits, class Duration, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

sys_time<Duration>& tp,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.clock.utc}, class \tcode{utc_clock}

class utc_clock;

template<class Duration>

using utc_time = time_point<utc_clock, Duration>;

using utc_seconds = utc_time<seconds>;

template<class charT, class traits, class Duration>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const utc_time<Duration>& t);

template<class charT, class traits, class Duration, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

utc_time<Duration>& tp,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

struct leap_second_info;

template<class Duration>

leap_second_info get_leap_second_info(const utc_time<Duration>& ut);

// \ref{time.clock.tai}, class \tcode{tai_clock}

class tai_clock;

template<class Duration>

using tai_time = time_point<tai_clock, Duration>;

using tai_seconds = tai_time<seconds>;

template<class charT, class traits, class Duration>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const tai_time<Duration>& t);

template<class charT, class traits, class Duration, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

tai_time<Duration>& tp,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.clock.gps}, class \tcode{gps_clock}

class gps_clock;

template<class Duration>

using gps_time = time_point<gps_clock, Duration>;

using gps_seconds = gps_time<seconds>;

template<class charT, class traits, class Duration>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const gps_time<Duration>& t);

template<class charT, class traits, class Duration, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

gps_time<Duration>& tp,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.clock.file}, type \tcode{file_clock}

using file_clock = @\seebelow@;

template<class Duration>

using file_time = time_point<file_clock, Duration>;

template<class charT, class traits, class Duration>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const file_time<Duration>& tp);

template<class charT, class traits, class Duration, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

file_time<Duration>& tp,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.clock.steady}, class \tcode{steady_clock}

class steady_clock;

// \ref{time.clock.hires}, class \tcode{high_resolution_clock}

class high_resolution_clock;

// \ref{time.clock.local}, local time

struct local_t {};

template<class Duration>

using local_time = time_point<local_t, Duration>;

using local_seconds = local_time<seconds>;

using local_days = local_time<days>;

template<class charT, class traits, class Duration>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const local_time<Duration>& tp);

template<class charT, class traits, class Duration, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

local_time<Duration>& tp,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.clock.cast}, \tcode{time_point} conversions

template<class DestClock, class SourceClock>

struct clock_time_conversion;

template<class DestClock, class SourceClock, class Duration>

auto clock_cast(const time_point<SourceClock, Duration>& t);

// \ref{time.cal.last}, class \tcode{last_spec}

struct last_spec;

// \ref{time.cal.day}, class \tcode{day}

class day;

constexpr bool operator==(const day& x, const day& y) noexcept;

constexpr strong_ordering operator<=>(const day& x, const day& y) noexcept;

constexpr day operator+(const day& x, const days& y) noexcept;

constexpr day operator+(const days& x, const day& y) noexcept;

constexpr day operator-(const day& x, const days& y) noexcept;

constexpr days operator-(const day& x, const day& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const day& d);

template<class charT, class traits, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

day& d, basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.cal.month}, class \tcode{month}

class month;

constexpr bool operator==(const month& x, const month& y) noexcept;

constexpr strong_ordering operator<=>(const month& x, const month& y) noexcept;

constexpr month operator+(const month& x, const months& y) noexcept;

constexpr month operator+(const months& x, const month& y) noexcept;

constexpr month operator-(const month& x, const months& y) noexcept;

constexpr months operator-(const month& x, const month& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const month& m);

template<class charT, class traits, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

month& m, basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.cal.year}, class \tcode{year}

class year;

constexpr bool operator==(const year& x, const year& y) noexcept;

constexpr strong_ordering operator<=>(const year& x, const year& y) noexcept;

constexpr year operator+(const year& x, const years& y) noexcept;

constexpr year operator+(const years& x, const year& y) noexcept;

constexpr year operator-(const year& x, const years& y) noexcept;

constexpr years operator-(const year& x, const year& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const year& y);

template<class charT, class traits, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

year& y, basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.cal.wd}, class \tcode{weekday}

class weekday;

constexpr bool operator==(const weekday& x, const weekday& y) noexcept;

constexpr weekday operator+(const weekday& x, const days& y) noexcept;

constexpr weekday operator+(const days& x, const weekday& y) noexcept;

constexpr weekday operator-(const weekday& x, const days& y) noexcept;

constexpr days operator-(const weekday& x, const weekday& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const weekday& wd);

template<class charT, class traits, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

weekday& wd, basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.cal.wdidx}, class \tcode{weekday_indexed}

class weekday_indexed;

constexpr bool operator==(const weekday_indexed& x, const weekday_indexed& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const weekday_indexed& wdi);

// \ref{time.cal.wdlast}, class \tcode{weekday_last}

class weekday_last;

constexpr bool operator==(const weekday_last& x, const weekday_last& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const weekday_last& wdl);

// \ref{time.cal.md}, class \tcode{month_day}

class month_day;

constexpr bool operator==(const month_day& x, const month_day& y) noexcept;

constexpr strong_ordering operator<=>(const month_day& x, const month_day& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const month_day& md);

template<class charT, class traits, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

month_day& md, basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.cal.mdlast}, class \tcode{month_day_last}

class month_day_last;

constexpr bool operator==(const month_day_last& x, const month_day_last& y) noexcept;

constexpr strong_ordering operator<=>(const month_day_last& x,

const month_day_last& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const month_day_last& mdl);

// \ref{time.cal.mwd}, class \tcode{month_weekday}

class month_weekday;

constexpr bool operator==(const month_weekday& x, const month_weekday& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const month_weekday& mwd);

// \ref{time.cal.mwdlast}, class \tcode{month_weekday_last}

class month_weekday_last;

constexpr bool operator==(const month_weekday_last& x, const month_weekday_last& y) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const month_weekday_last& mwdl);

// \ref{time.cal.ym}, class \tcode{year_month}

class year_month;

constexpr bool operator==(const year_month& x, const year_month& y) noexcept;

constexpr strong_ordering operator<=>(const year_month& x, const year_month& y) noexcept;

constexpr year_month operator+(const year_month& ym, const months& dm) noexcept;

constexpr year_month operator+(const months& dm, const year_month& ym) noexcept;

constexpr year_month operator-(const year_month& ym, const months& dm) noexcept;

constexpr months operator-(const year_month& x, const year_month& y) noexcept;

constexpr year_month operator+(const year_month& ym, const years& dy) noexcept;

constexpr year_month operator+(const years& dy, const year_month& ym) noexcept;

constexpr year_month operator-(const year_month& ym, const years& dy) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const year_month& ym);

template<class charT, class traits, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

year_month& ym, basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.cal.ymd}, class \tcode{year_month_day}

class year_month_day;

constexpr bool operator==(const year_month_day& x, const year_month_day& y) noexcept;

constexpr strong_ordering operator<=>(const year_month_day& x,

const year_month_day& y) noexcept;

constexpr year_month_day operator+(const year_month_day& ymd, const months& dm) noexcept;

constexpr year_month_day operator+(const months& dm, const year_month_day& ymd) noexcept;

constexpr year_month_day operator+(const year_month_day& ymd, const years& dy) noexcept;

constexpr year_month_day operator+(const years& dy, const year_month_day& ymd) noexcept;

constexpr year_month_day operator-(const year_month_day& ymd, const months& dm) noexcept;

constexpr year_month_day operator-(const year_month_day& ymd, const years& dy) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const year_month_day& ymd);

template<class charT, class traits, class Alloc = allocator<charT>>

basic_istream<charT, traits>&

from_stream(basic_istream<charT, traits>& is, const charT* fmt,

year_month_day& ymd,

basic_string<charT, traits, Alloc>* abbrev = nullptr,

minutes* offset = nullptr);

// \ref{time.cal.ymdlast}, class \tcode{year_month_day_last}

class year_month_day_last;

constexpr bool operator==(const year_month_day_last& x,

const year_month_day_last& y) noexcept;

constexpr strong_ordering operator<=>(const year_month_day_last& x,

const year_month_day_last& y) noexcept;

constexpr year_month_day_last

operator+(const year_month_day_last& ymdl, const months& dm) noexcept;

constexpr year_month_day_last

operator+(const months& dm, const year_month_day_last& ymdl) noexcept;

constexpr year_month_day_last

operator+(const year_month_day_last& ymdl, const years& dy) noexcept;

constexpr year_month_day_last

operator+(const years& dy, const year_month_day_last& ymdl) noexcept;

constexpr year_month_day_last

operator-(const year_month_day_last& ymdl, const months& dm) noexcept;

constexpr year_month_day_last

operator-(const year_month_day_last& ymdl, const years& dy) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const year_month_day_last& ymdl);

// \ref{time.cal.ymwd}, class \tcode{year_month_weekday}

class year_month_weekday;

constexpr bool operator==(const year_month_weekday& x,

const year_month_weekday& y) noexcept;

constexpr year_month_weekday

operator+(const year_month_weekday& ymwd, const months& dm) noexcept;

constexpr year_month_weekday

operator+(const months& dm, const year_month_weekday& ymwd) noexcept;

constexpr year_month_weekday

operator+(const year_month_weekday& ymwd, const years& dy) noexcept;

constexpr year_month_weekday

operator+(const years& dy, const year_month_weekday& ymwd) noexcept;

constexpr year_month_weekday

operator-(const year_month_weekday& ymwd, const months& dm) noexcept;

constexpr year_month_weekday

operator-(const year_month_weekday& ymwd, const years& dy) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const year_month_weekday& ymwd);

// \ref{time.cal.ymwdlast}, class \tcode{year_month_weekday_last}

class year_month_weekday_last;

constexpr bool operator==(const year_month_weekday_last& x,

const year_month_weekday_last& y) noexcept;

constexpr year_month_weekday_last

operator+(const year_month_weekday_last& ymwdl, const months& dm) noexcept;

constexpr year_month_weekday_last

operator+(const months& dm, const year_month_weekday_last& ymwdl) noexcept;

constexpr year_month_weekday_last

operator+(const year_month_weekday_last& ymwdl, const years& dy) noexcept;

constexpr year_month_weekday_last

operator+(const years& dy, const year_month_weekday_last& ymwdl) noexcept;

constexpr year_month_weekday_last

operator-(const year_month_weekday_last& ymwdl, const months& dm) noexcept;

constexpr year_month_weekday_last

operator-(const year_month_weekday_last& ymwdl, const years& dy) noexcept;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const year_month_weekday_last& ymwdl);

// \ref{time.cal.operators}, civil calendar conventional syntax operators

constexpr year_month

operator/(const year& y, const month& m) noexcept;

constexpr year_month

operator/(const year& y, int m) noexcept;

constexpr month_day

operator/(const month& m, const day& d) noexcept;

constexpr month_day

operator/(const month& m, int d) noexcept;

constexpr month_day

operator/(int m, const day& d) noexcept;

constexpr month_day

operator/(const day& d, const month& m) noexcept;

constexpr month_day

operator/(const day& d, int m) noexcept;

constexpr month_day_last

operator/(const month& m, last_spec) noexcept;

constexpr month_day_last

operator/(int m, last_spec) noexcept;

constexpr month_day_last

operator/(last_spec, const month& m) noexcept;

constexpr month_day_last

operator/(last_spec, int m) noexcept;

constexpr month_weekday

operator/(const month& m, const weekday_indexed& wdi) noexcept;

constexpr month_weekday

operator/(int m, const weekday_indexed& wdi) noexcept;

constexpr month_weekday

operator/(const weekday_indexed& wdi, const month& m) noexcept;

constexpr month_weekday

operator/(const weekday_indexed& wdi, int m) noexcept;

constexpr month_weekday_last

operator/(const month& m, const weekday_last& wdl) noexcept;

constexpr month_weekday_last

operator/(int m, const weekday_last& wdl) noexcept;

constexpr month_weekday_last

operator/(const weekday_last& wdl, const month& m) noexcept;

constexpr month_weekday_last

operator/(const weekday_last& wdl, int m) noexcept;

constexpr year_month_day

operator/(const year_month& ym, const day& d) noexcept;

constexpr year_month_day

operator/(const year_month& ym, int d) noexcept;

constexpr year_month_day

operator/(const year& y, const month_day& md) noexcept;

constexpr year_month_day

operator/(int y, const month_day& md) noexcept;

constexpr year_month_day

operator/(const month_day& md, const year& y) noexcept;

constexpr year_month_day

operator/(const month_day& md, int y) noexcept;

constexpr year_month_day_last

operator/(const year_month& ym, last_spec) noexcept;

constexpr year_month_day_last

operator/(const year& y, const month_day_last& mdl) noexcept;

constexpr year_month_day_last

operator/(int y, const month_day_last& mdl) noexcept;

constexpr year_month_day_last

operator/(const month_day_last& mdl, const year& y) noexcept;

constexpr year_month_day_last

operator/(const month_day_last& mdl, int y) noexcept;

constexpr year_month_weekday

operator/(const year_month& ym, const weekday_indexed& wdi) noexcept;

constexpr year_month_weekday

operator/(const year& y, const month_weekday& mwd) noexcept;

constexpr year_month_weekday

operator/(int y, const month_weekday& mwd) noexcept;

constexpr year_month_weekday

operator/(const month_weekday& mwd, const year& y) noexcept;

constexpr year_month_weekday

operator/(const month_weekday& mwd, int y) noexcept;

constexpr year_month_weekday_last

operator/(const year_month& ym, const weekday_last& wdl) noexcept;

constexpr year_month_weekday_last

operator/(const year& y, const month_weekday_last& mwdl) noexcept;

constexpr year_month_weekday_last

operator/(int y, const month_weekday_last& mwdl) noexcept;

constexpr year_month_weekday_last

operator/(const month_weekday_last& mwdl, const year& y) noexcept;

constexpr year_month_weekday_last

operator/(const month_weekday_last& mwdl, int y) noexcept;

// \ref{time.hms}, class template \tcode{hh_mm_ss}

template<class Duration> class hh_mm_ss;

template<class charT, class traits, class Duration>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const hh_mm_ss<Duration>& hms);

// \ref{time.12}, 12/24 hour functions

constexpr bool is_am(const hours& h) noexcept;

constexpr bool is_pm(const hours& h) noexcept;

constexpr hours make12(const hours& h) noexcept;

constexpr hours make24(const hours& h, bool is_pm) noexcept;

// \ref{time.zone.db}, time zone database

struct tzdb;

class tzdb_list;

// \ref{time.zone.db.access}, time zone database access

const tzdb& get_tzdb();

tzdb_list& get_tzdb_list();

const time_zone* locate_zone(string_view tz_name);

const time_zone* current_zone();

// \ref{time.zone.db.remote}, remote time zone database support

const tzdb& reload_tzdb();

string remote_version();

// \ref{time.zone.exception}, exception classes

class nonexistent_local_time;

class ambiguous_local_time;

// \ref{time.zone.info}, information classes

struct sys_info;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const sys_info& si);

struct local_info;

template<class charT, class traits>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os, const local_info& li);

// \ref{time.zone.timezone}, class \tcode{time_zone}

enum class choose {earliest, latest};

class time_zone;

bool operator==(const time_zone& x, const time_zone& y) noexcept;

strong_ordering operator<=>(const time_zone& x, const time_zone& y) noexcept;

// \ref{time.zone.zonedtraits}, class template \tcode{zoned_traits}

template<class T> struct zoned_traits;

// \ref{time.zone.zonedtime}, class template \tcode{zoned_time}

template<class Duration, class TimeZonePtr = const time_zone*> class zoned_time;

using zoned_seconds = zoned_time<seconds>;

template<class Duration1, class Duration2, class TimeZonePtr>

bool operator==(const zoned_time<Duration1, TimeZonePtr>& x,

const zoned_time<Duration2, TimeZonePtr>& y);

template<class charT, class traits, class Duration, class TimeZonePtr>

basic_ostream<charT, traits>&

operator<<(basic_ostream<charT, traits>& os,

const zoned_time<Duration, TimeZonePtr>& t);

// \ref{time.zone.leap}, leap second support

class leap_second;

constexpr bool operator==(const leap_second& x, const leap_second& y);

constexpr strong_ordering operator<=>(const leap_second& x, const leap_second& y);

template<class Duration>

constexpr bool operator==(const leap_second& x, const sys_time<Duration>& y);

template<class Duration>

constexpr bool operator< (const leap_second& x, const sys_time<Duration>& y);

template<class Duration>

constexpr bool operator< (const sys_time<Duration>& x, const leap_second& y);

template<class Duration>

constexpr bool operator> (const leap_second& x, const sys_time<Duration>& y);

template<class Duration>

constexpr bool operator> (const sys_time<Duration>& x, const leap_second& y);

template<class Duration>

constexpr bool operator<=(const leap_second& x, const sys_time<Duration>& y);

template<class Duration>

constexpr bool operator<=(const sys_time<Duration>& x, const leap_second& y);

template<class Duration>

constexpr bool operator>=(const leap_second& x, const sys_time<Duration>& y);

template<class Duration>

constexpr bool operator>=(const sys_time<Duration>& x, const leap_second& y);

template<class Duration>

requires @\libconcept{three_way_comparable_with}@<sys_seconds, sys_time<Duration>>

constexpr auto operator<=>(const leap_second& x, const sys_time<Duration>& y);

// \ref{time.zone.link}, class \tcode{time_zone_link}

class time_zone_link;

bool operator==(const time_zone_link& x, const time_zone_link& y);

strong_ordering operator<=>(const time_zone_link& x, const time_zone_link& y);

// \ref{time.format}, formatting

template<class Duration> struct @\placeholder{local-time-format-t}@; // \expos

template<class Duration>

@\placeholder{local-time-format-t}@<Duration>

local_time_format(local_time<Duration> time, const string* abbrev = nullptr,

const seconds* offset_sec = nullptr);

}

namespace std {

template<class Rep, class Period, class charT>

struct formatter<chrono::duration<Rep, Period>, charT>;

template<class Duration, class charT>

struct formatter<chrono::sys_time<Duration>, charT>;

template<class Duration, class charT>

struct formatter<chrono::utc_time<Duration>, charT>;

template<class Duration, class charT>

struct formatter<chrono::tai_time<Duration>, charT>;

template<class Duration, class charT>

struct formatter<chrono::gps_time<Duration>, charT>;

template<class Duration, class charT>

struct formatter<chrono::file_time<Duration>, charT>;

template<class Duration, class charT>

struct formatter<chrono::local_time<Duration>, charT>;

template<class Duration, class charT>

struct formatter<chrono::@\placeholder{local-time-format-t}@<Duration>, charT>;

template<class charT> struct formatter<chrono::day, charT>;

template<class charT> struct formatter<chrono::month, charT>;

template<class charT> struct formatter<chrono::year, charT>;

template<class charT> struct formatter<chrono::weekday, charT>;

template<class charT> struct formatter<chrono::weekday_indexed, charT>;

template<class charT> struct formatter<chrono::weekday_last, charT>;

template<class charT> struct formatter<chrono::month_day, charT>;

template<class charT> struct formatter<chrono::month_day_last, charT>;

template<class charT> struct formatter<chrono::month_weekday, charT>;

template<class charT> struct formatter<chrono::month_weekday_last, charT>;

template<class charT> struct formatter<chrono::year_month, charT>;

template<class charT> struct formatter<chrono::year_month_day, charT>;

template<class charT> struct formatter<chrono::year_month_day_last, charT>;

template<class charT> struct formatter<chrono::year_month_weekday, charT>;

template<class charT> struct formatter<chrono::year_month_weekday_last, charT>;

template<class Rep, class Period, class charT>

struct formatter<chrono::hh_mm_ss<duration<Rep, Period>>, charT>;

template<class charT> struct formatter<chrono::sys_info, charT>;

template<class charT> struct formatter<chrono::local_info, charT>;

template<class Duration, class TimeZonePtr, class charT>

struct formatter<chrono::zoned_time<Duration, TimeZonePtr>, charT>;

}

namespace std::chrono {

// \ref{time.parse}, parsing

template<class charT, class Parsable>

@\unspec@

parse(const charT* fmt, Parsable& tp);

template<class charT, class traits, class Alloc, class Parsable>

@\unspec@

parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp);

template<class charT, class traits, class Alloc, class Parsable>

@\unspec@

parse(const charT* fmt, Parsable& tp,

basic_string<charT, traits, Alloc>& abbrev);

template<class charT, class traits, class Alloc, class Parsable>

@\unspec@

parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,

basic_string<charT, traits, Alloc>& abbrev);

template<class charT, class Parsable>

@\unspec@

parse(const charT* fmt, Parsable& tp, minutes& offset);

template<class charT, class traits, class Alloc, class Parsable>

@\unspec@

parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,

minutes& offset);

template<class charT, class traits, class Alloc, class Parsable>

@\unspec@

parse(const charT* fmt, Parsable& tp,

basic_string<charT, traits, Alloc>& abbrev, minutes& offset);

template<class charT, class traits, class Alloc, class Parsable>

@\unspec@

parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,

basic_string<charT, traits, Alloc>& abbrev, minutes& offset);

// calendrical constants

inline constexpr last_spec last{};

inline constexpr weekday Sunday{0};

inline constexpr weekday Monday{1};

inline constexpr weekday Tuesday{2};

inline constexpr weekday Wednesday{3};

inline constexpr weekday Thursday{4};

inline constexpr weekday Friday{5};

inline constexpr weekday Saturday{6};

inline constexpr month January{1};

inline constexpr month February{2};

inline constexpr month March{3};

inline constexpr month April{4};

inline constexpr month May{5};

inline constexpr month June{6};

inline constexpr month July{7};

inline constexpr month August{8};

inline constexpr month September{9};

inline constexpr month October{10};

inline constexpr month November{11};

inline constexpr month December{12};

}

namespace std::inline literals::inline chrono_literals {

// \ref{time.duration.literals}, suffixes for duration literals

constexpr chrono::hours operator""h(unsigned long long);

constexpr chrono::duration<@\unspec,@ ratio<3600, 1>> operator""h(long double);

constexpr chrono::minutes operator""min(unsigned long long);

constexpr chrono::duration<@\unspec,@ ratio<60, 1>> operator""min(long double);

constexpr chrono::seconds operator""s(unsigned long long);

constexpr chrono::duration<@\unspec@>@\itcorr[-1]@ operator""s(long double);

constexpr chrono::milliseconds operator""ms(unsigned long long);

constexpr chrono::duration<@\unspec,@ milli> operator""ms(long double);

constexpr chrono::microseconds operator""us(unsigned long long);

constexpr chrono::duration<@\unspec,@ micro> operator""us(long double);

constexpr chrono::nanoseconds operator""ns(unsigned long long);

constexpr chrono::duration<@\unspec,@ nano> operator""ns(long double);

// \ref{time.cal.day.nonmembers}, non-member functions

constexpr chrono::day operator""d(unsigned long long d) noexcept;

// \ref{time.cal.year.nonmembers}, non-member functions

constexpr chrono::year operator""y(unsigned long long y) noexcept;

}

namespace std::chrono {

using namespace literals::chrono_literals;

}

namespace std {

// \ref{time.hash}, hash support

template<class T> struct hash;

template<class Rep, class Period> struct hash<chrono::duration<Rep, Period>>;

template<class Clock, class Duration> struct hash<chrono::time_point<Clock, Duration>>;

template<> struct hash<chrono::day>;

template<> struct hash<chrono::month>;

template<> struct hash<chrono::year>;

template<> struct hash<chrono::weekday>;

template<> struct hash<chrono::weekday_indexed>;

template<> struct hash<chrono::weekday_last>;

template<> struct hash<chrono::month_day>;

template<> struct hash<chrono::month_day_last>;

template<> struct hash<chrono::month_weekday>;

template<> struct hash<chrono::month_weekday_last>;

template<> struct hash<chrono::year_month>;

template<> struct hash<chrono::year_month_day>;

template<> struct hash<chrono::year_month_day_last>;

template<> struct hash<chrono::year_month_weekday>;

template<> struct hash<chrono::year_month_weekday_last>;

template<class Duration, class TimeZonePtr>

struct hash<chrono::zoned_time<Duration, TimeZonePtr>>;

template<> struct hash<chrono::leap_second>;

}

\end{codeblock}

\rSec1[time.clock.req]{\oldconcept{Clock} requirements}

\indextext{\idxoldconcept{Clock}}%

A clock is a bundle consisting of a \tcode{duration}, a

\tcode{time_point}, and a function \tcode{now()} to get the current \tcode{time_point}.

The origin of the clock's \tcode{time_point} is referred to as the clock's \defn{epoch}.

A clock shall meet the requirements in \tref{time.clock}.

In \tref{time.clock} \tcode{C1} and \tcode{C2} denote clock types. \tcode{t1} and

\tcode{t2} are values returned by \tcode{C1::now()} where the call returning \tcode{t1} happens

before\iref{intro.multithread} the call returning \tcode{t2} and both of these calls

occur

before \tcode{C1::time_point::max()}.

\begin{note}

This means \tcode{C1} did not wrap around between \tcode{t1} and

\tcode{t2}.

\end{note}

\begin{libreqtab3a}

{\oldconcept{Clock} requirements}

{time.clock}

\\ \topline

\lhdr{Expression} & \chdr{Return type} & \rhdr{Operational semantics} \\ \capsep