30 Time library [time]

30.1 General [time.general]

This Clause describes the chrono library ([time.syn]) and various C functions ([ctime.syn]) that provide generally useful time utilities, as summarized in Table 125 .

Table 125 — Time library summary [tab:time.summary]

🔗	Subclause	Header
🔗 [time.clock.req]	Cpp17Clock requirements
🔗 [time.traits]	Time-related traits	<chrono>
🔗 [time.duration]	Class template duration
🔗 [time.point]	Class template time_point
🔗 [time.clock]	Clocks
🔗 [time.cal]	Civil calendar
🔗 [time.hms]	Class template hh_mm_ss
🔗 [time.12]	12/24 hour functions
🔗 [time.zone]	Time zones
🔗 [time.format]	Formatting
🔗 [time.parse]	Parsing
🔗 [time.hash]	Hash support
🔗 [ctime.syn]	C library time utilities	<ctime>

Let STATICALLY-WIDEN<charT>("...") be "..." if charT is char and L"..." if charT is wchar_t.

30.2 Header <chrono> synopsis [time.syn]

🔗

#include <compare> // see [compare.syn] namespace std::chrono { // [time.duration], class template duration template<class Rep, class Period = ratio<1>> class duration; // [time.point], class template time_point template<class Clock, class Duration = typename Clock::duration> class time_point; } namespace std { // [time.traits.specializations], 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 { // [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; // [time.duration.nonmember], 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); // [time.duration.comparisons], 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 see below constexpr auto operator<=>(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs); // [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); // [time.duration.io], 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<signed integer type of at least 64 bits, nano>; using microseconds = duration<signed integer type of at least 55 bits, micro>; using milliseconds = duration<signed integer type of at least 45 bits, milli>; using seconds = duration<signed integer type of at least 35 bits>; using minutes = duration<signed integer type of at least 29 bits, ratio< 60>>; using hours = duration<signed integer type of at least 23 bits, ratio<3600>>; using days = duration<signed integer type of at least 25 bits, ratio_multiply<ratio<24>, hours::period>>; using weeks = duration<signed integer type of at least 22 bits, ratio_multiply<ratio<7>, days::period>>; using years = duration<signed integer type of at least 17 bits, ratio_multiply<ratio<146097, 400>, days::period>>; using months = duration<signed integer type of at least 20 bits, ratio_divide<years::period, ratio<12>>>; // [time.point.nonmember], 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); // [time.point.comparisons], 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, three_way_comparable_with<Duration1> Duration2> constexpr auto operator<=>(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs); // [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); // [time.duration.alg], specialized algorithms template<class Rep, class Period> constexpr duration<Rep, Period> abs(duration<Rep, Period> d); // [time.clock.system], class 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); // [time.clock.utc], class 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); // [time.clock.tai], class 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); // [time.clock.gps], class 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); // [time.clock.file], type file_clock using file_clock = see below; 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); // [time.clock.steady], class steady_clock class steady_clock; // [time.clock.hires], class high_resolution_clock class high_resolution_clock; // [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); // [time.clock.cast], 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); // [time.cal.last], class last_spec struct last_spec; // [time.cal.day], class 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); // [time.cal.month], class 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); // [time.cal.year], class 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); // [time.cal.wd], class 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); // [time.cal.wdidx], class 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); // [time.cal.wdlast], class 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); // [time.cal.md], class 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); // [time.cal.mdlast], class 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); // [time.cal.mwd], class 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); // [time.cal.mwdlast], class 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); // [time.cal.ym], class 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); // [time.cal.ymd], class 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); // [time.cal.ymdlast], class 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); // [time.cal.ymwd], class 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); // [time.cal.ymwdlast], class 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); // [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; // [time.hms], class template 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); // [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; // [time.zone.db], time zone database struct tzdb; class tzdb_list; // [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(); // [time.zone.db.remote], remote time zone database support const tzdb& reload_tzdb(); string remote_version(); // [time.zone.exception], exception classes class nonexistent_local_time; class ambiguous_local_time; // [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); // [time.zone.timezone], class 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; // [time.zone.zonedtraits], class template zoned_traits template<class T> struct zoned_traits; // [time.zone.zonedtime], class template 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); // [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 three_way_comparable_with<sys_seconds, sys_time<Duration>> constexpr auto operator<=>(const leap_second& x, const sys_time<Duration>& y); // [time.zone.link], class 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); // [time.format], formatting template<class Duration> struct local-time-format-t; // exposition only template<class Duration> 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::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 { // [time.parse], parsing template<class charT, class Parsable> unspecified parse(const charT* fmt, Parsable& tp); template<class charT, class traits, class Alloc, class Parsable> unspecified parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp); template<class charT, class traits, class Alloc, class Parsable> unspecified parse(const charT* fmt, Parsable& tp, basic_string<charT, traits, Alloc>& abbrev); template<class charT, class traits, class Alloc, class Parsable> unspecified parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp, basic_string<charT, traits, Alloc>& abbrev); template<class charT, class Parsable> unspecified parse(const charT* fmt, Parsable& tp, minutes& offset); template<class charT, class traits, class Alloc, class Parsable> unspecified parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp, minutes& offset); template<class charT, class traits, class Alloc, class Parsable> unspecified parse(const charT* fmt, Parsable& tp, basic_string<charT, traits, Alloc>& abbrev, minutes& offset); template<class charT, class traits, class Alloc, class Parsable> unspecified 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 { // [time.duration.literals], suffixes for duration literals constexpr chrono::hours operator""h(unsigned long long); constexpr chrono::duration<unspecified, ratio<3600, 1>> operator""h(long double); constexpr chrono::minutes operator""min(unsigned long long); constexpr chrono::duration<unspecified, ratio<60, 1>> operator""min(long double); constexpr chrono::seconds operator""s(unsigned long long); constexpr chrono::duration<unspecified> operator""s(long double); constexpr chrono::milliseconds operator""ms(unsigned long long); constexpr chrono::duration<unspecified, milli> operator""ms(long double); constexpr chrono::microseconds operator""us(unsigned long long); constexpr chrono::duration<unspecified, micro> operator""us(long double); constexpr chrono::nanoseconds operator""ns(unsigned long long); constexpr chrono::duration<unspecified, nano> operator""ns(long double); // [time.cal.day.nonmembers], non-member functions constexpr chrono::day operator""d(unsigned long long d) noexcept; // [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 { // [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>; }

30.3 Cpp17Clock requirements [time.clock.req]

A clock is a bundle consisting of a duration, a time_point, and a function now() to get the current time_point.

The origin of the clock's time_point is referred to as the clock's epoch.

A clock shall meet the requirements in Table 126 .

In Table 126 C1 and C2 denote clock types.

t1 and t2 are values returned by C1::now() where the call returning t1 happens before ([intro.multithread]) the call returning t2 and both of these calls occur before C1::time_point::max().

[Note 1:

This means C1 did not wrap around between t1 and t2.

— end note]

Table 126 — Cpp17Clock requirements [tab:time.clock]

🔗 Expression	Return type	Operational semantics
🔗 C1::rep	An arithmetic type or a class emulating an arithmetic type	The representation type of C1::duration.
🔗 C1::period	a specialization of ratio	The tick period of the clock in seconds.
🔗 C1::duration	chrono::duration<C1::rep, C1::period>	The duration type of the clock.
🔗 C1::time_point	chrono::time_point<C1> or chrono::time_point<C2, C1::duration>	The time_point type of the clock. C1 and C2 shall refer to the same epoch.
🔗 C1::is_steady	const bool	true if t1 <= t2 is always true and the time between clock ticks is constant, otherwise false.
🔗 C1::now()	C1::time_point	Returns a time_point object representing the current point in time.

[Note 2:

The relative difference in durations between those reported by a given clock and the SI definition is a measure of the quality of implementation.

— end note]

A type TC meets the Cpp17TrivialClock requirements if

(4.1)
TC meets the Cpp17Clock requirements,
(4.2)
the types TC::rep, TC::duration, and TC::time_point meet the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) and Cpp17Swappable ([swappable.requirements]) requirements and the requirements of numeric types ([numeric.requirements]),
[Note 3:
This means, in particular, that operations on these types will not throw exceptions.
— end note]
(4.3)
the function TC::now() does not throw exceptions, and
(4.4)
the type TC::time_point::clock meets the Cpp17TrivialClock requirements, recursively.

30.4 Time-related traits [time.traits]

30.4.1 treat_as_floating_point [time.traits.is.fp]

🔗

template<class Rep> struct treat_as_floating_point : is_floating_point<Rep> { };

The duration template uses the treat_as_floating_point trait to help determine if a duration object can be converted to another duration with a different tick period.

If treat_as_floating_point_v<Rep> is true, then implicit conversions are allowed among durations.

Otherwise, the implicit convertibility depends on the tick periods of the durations.

[Note 1:

The intention of this trait is to indicate whether a given class behaves like a floating-point type, and thus allows division of one value by another with acceptable loss of precision.

If treat_as_floating_point_v<Rep> is false, Rep will be treated as if it behaved like an integral type for the purpose of these conversions.

— end note]

30.4.2 duration_values [time.traits.duration.values]

🔗

template<class Rep>
  struct duration_values {
  public:
    static constexpr Rep zero() noexcept;
    static constexpr Rep min() noexcept;
    static constexpr Rep max() noexcept;
  };

The duration template uses the duration_values trait to construct special values of the duration's representation (Rep).

This is done because the representation can be a class type with behavior that requires some other implementation to return these special values.

In that case, the author of that class type should specialize duration_values to return the indicated values.

🔗

static constexpr Rep zero() noexcept;

Returns: Rep(0).

[Note 1:

Rep(0) is specified instead of Rep() because Rep() can have some other meaning, such as an uninitialized value.

— end note]

Remarks: The value returned shall be the additive identity.

🔗

static constexpr Rep min() noexcept;

Returns: numeric_limits<Rep>::lowest().

Remarks: The value returned shall compare less than or equal to zero().

🔗

static constexpr Rep max() noexcept;

Returns: numeric_limits<Rep>::max().

Remarks: The value returned shall compare greater than zero().

30.4.3 Specializations of common_type [time.traits.specializations]

🔗

template<class Rep1, class Period1, class Rep2, class Period2>
  struct common_type<chrono::duration<Rep1, Period1>, chrono::duration<Rep2, Period2>> {
    using type = chrono::duration<common_type_t<Rep1, Rep2>, see below>;
  };

The period of the duration indicated by this specialization of common_type is the greatest common divisor of Period1 and Period2.

[Note 1:

This can be computed by forming a ratio of the greatest common divisor of Period1::num and Period2::num and the least common multiple of Period1::den and Period2::den.

— end note]

[Note 2:

The typedef name type is a synonym for the duration with the largest tick period possible where both duration arguments will convert to it without requiring a division operation.

The representation of this type is intended to be able to hold any value resulting from this conversion with no truncation error, although floating-point durations can have round-off errors.

— end note]

🔗

template<class Clock, class Duration1, class Duration2>
  struct common_type<chrono::time_point<Clock, Duration1>, chrono::time_point<Clock, Duration2>> {
    using type = chrono::time_point<Clock, common_type_t<Duration1, Duration2>>;
  };

The common type of two time_point types is a time_point with the same clock as the two types and the common type of their two durations.

30.4.4 Class template is_clock [time.traits.is.clock]

🔗

template<class T> struct is_clock;

is_clock is a Cpp17UnaryTypeTrait ([meta.rqmts]) with a base characteristic of true_type if T meets the Cpp17Clock requirements ([time.clock.req]), otherwise false_type.

For the purposes of the specification of this trait, the extent to which an implementation determines that a type cannot meet the Cpp17Clock requirements is unspecified, except that as a minimum a type T shall not qualify as a Cpp17Clock unless it meets all of the following conditions:

(1.1)
the qualified-ids T::rep, T::period, T::duration, and T::time_point are valid and each denotes a type ([temp.deduct]),
(1.2)
the expression T::is_steady is well-formed when treated as an unevaluated operand,
(1.3)
the expression T::now() is well-formed when treated as an unevaluated operand.

The behavior of a program that adds specializations for is_clock is undefined.

30.5 Class template duration [time.duration]

30.5.1 General [time.duration.general]

A duration type measures time between two points in time (time_points).

A duration has a representation which holds a count of ticks and a tick period.

The tick period is the amount of time which occurs from one tick to the next, in units of seconds.

It is expressed as a rational constant using the template ratio.

🔗

namespace std::chrono { template<class Rep, class Period = ratio<1>> class duration { public: using rep = Rep; using period = typename Period::type; private: rep rep_; // exposition only public: // [time.duration.cons], construct/copy/destroy constexpr duration() = default; template<class Rep2> constexpr explicit duration(const Rep2& r); template<class Rep2, class Period2> constexpr duration(const duration<Rep2, Period2>& d); ~duration() = default; duration(const duration&) = default; duration& operator=(const duration&) = default; // [time.duration.observer], observer constexpr rep count() const; // [time.duration.arithmetic], arithmetic constexpr common_type_t<duration> operator+() const; constexpr common_type_t<duration> operator-() const; constexpr duration& operator++(); constexpr duration operator++(int); constexpr duration& operator--(); constexpr duration operator--(int); constexpr duration& operator+=(const duration& d); constexpr duration& operator-=(const duration& d); constexpr duration& operator*=(const rep& rhs); constexpr duration& operator/=(const rep& rhs); constexpr duration& operator%=(const rep& rhs); constexpr duration& operator%=(const duration& rhs); // [time.duration.special], special values static constexpr duration zero() noexcept; static constexpr duration min() noexcept; static constexpr duration max() noexcept; }; }

Rep shall be an arithmetic type or a class emulating an arithmetic type.

If duration is instantiated with a duration type as the argument for the template parameter Rep, the program is ill-formed.

If Period is not a specialization of ratio, the program is ill-formed.

If Period::num is not positive, the program is ill-formed.

Members of duration do not throw exceptions other than those thrown by the indicated operations on their representations.

The defaulted copy constructor of duration shall be a constexpr function if and only if the required initialization of the member rep_ for copy and move, respectively, would be constexpr-suitable ([dcl.constexpr]).

[Example 1: duration<long, ratio<60>> d0; // holds a count of minutes using a long duration<long long, milli> d1; // holds a count of milliseconds using a long long duration<double, ratio<1, 30>> d2; // holds a count with a tick period of

\frac{1}{30}

of a second // (30 Hz) using a double — end example]

30.5.2 Constructors [time.duration.cons]

🔗

template<class Rep2>
  constexpr explicit duration(const Rep2& r);

Constraints: is_convertible_v<const Rep2&, rep> is true and

(1.1)
treat_as_floating_point_v<rep> is true or
(1.2)
treat_as_floating_point_v<Rep2> is false.

[Example 1: duration<int, milli> d(3); // OK duration<int, milli> d2(3.5); // error — end example]

Effects: Initializes rep_ with r.

🔗

template<class Rep2, class Period2>
  constexpr duration(const duration<Rep2, Period2>& d);

Constraints: No overflow is induced in the conversion and treat_as_floating_point_v<rep> is true or both ratio_divide<Period2, period>::den is 1 and treat_as_floating_point_v<Rep2> is false.

[Note 1:

This requirement prevents implicit truncation error when converting between integral-based duration types.

Such a construction could easily lead to confusion about the value of the duration.

— end note]

[Example 2: duration<int, milli> ms(3); duration<int, micro> us = ms; // OK duration<int, milli> ms2 = us; // error — end example]

Effects: Initializes rep_ with duration_cast<duration>(d).count().

30.5.3 Observer [time.duration.observer]

🔗

constexpr rep count() const;

Returns: rep_.

30.5.4 Arithmetic [time.duration.arithmetic]

🔗

constexpr common_type_t<duration> operator+() const;

Returns: common_type_t<duration>(*this).

🔗

constexpr common_type_t<duration> operator-() const;

Returns: common_type_t<duration>(-rep_).

🔗

constexpr duration& operator++();

Effects: Equivalent to: ++rep_.

Returns: *this.

🔗

constexpr duration operator++(int);

Effects: Equivalent to: return duration(rep_++);

🔗

constexpr duration& operator--();

Effects: Equivalent to: --rep_.

Returns: *this.

🔗

constexpr duration operator--(int);

Effects: Equivalent to: return duration(rep_--);

🔗

constexpr duration& operator+=(const duration& d);

Effects: Equivalent to: rep_ += d.count().

Returns: *this.

🔗

constexpr duration& operator-=(const duration& d);

Effects: Equivalent to: rep_ -= d.count().

Returns: *this.

🔗

constexpr duration& operator*=(const rep& rhs);

Effects: Equivalent to: rep_ *= rhs.

Returns: *this.

🔗

constexpr duration& operator/=(const rep& rhs);

Effects: Equivalent to: rep_ /= rhs.

Returns: *this.

🔗

constexpr duration& operator%=(const rep& rhs);

Effects: Equivalent to: rep_ %= rhs.

Returns: *this.

🔗

constexpr duration& operator%=(const duration& rhs);

Effects: Equivalent to: rep_ %= rhs.count().

Returns: *this.

30.5.5 Special values [time.duration.special]

🔗

static constexpr duration zero() noexcept;

Returns: duration(duration_values<rep>::zero()).

🔗

static constexpr duration min() noexcept;

Returns: duration(duration_values<rep>::min()).

🔗

static constexpr duration max() noexcept;

Returns: duration(duration_values<rep>::max()).

30.5.6 Non-member arithmetic [time.duration.nonmember]

In the function descriptions that follow, unless stated otherwise, let CD represent the return type of the function.

🔗

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);

Returns: CD(CD(lhs).count() + CD(rhs).count()).

🔗

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);

Returns: CD(CD(lhs).count() - CD(rhs).count()).

🔗

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

Constraints: is_convertible_v<const Rep2&, common_type_t<Rep1, Rep2>> is true.

Returns: CD(CD(d).count() * 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);

Constraints: is_convertible_v<const Rep1&, common_type_t<Rep1, Rep2>> is true.

Returns: d * s.

🔗

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

Constraints: is_convertible_v<const Rep2&, common_type_t<Rep1, Rep2>> is true and Rep2 is not a specialization of duration.

Returns: CD(CD(d).count() / 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);

Let CD be common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>.

Returns: CD(lhs).count() / CD(rhs).count().

🔗

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

Constraints: is_convertible_v<const Rep2&, common_type_t<Rep1, Rep2>> is true and Rep2 is not a specialization of duration.

Returns: CD(CD(d).count() % 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);

Returns: CD(CD(lhs).count() % CD(rhs).count()).

30.5.7 Comparisons [time.duration.comparisons]

In the function descriptions that follow, CT represents common_type_t<A, B>, where A and B are the types of the two arguments to the function.

🔗

template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator==(const duration<Rep1, Period1>& lhs,
                            const duration<Rep2, Period2>& rhs);

Returns: CT(lhs).count() == CT(rhs).count().

🔗

template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator<(const duration<Rep1, Period1>& lhs,
                           const duration<Rep2, Period2>& rhs);

Returns: CT(lhs).count() < CT(rhs).count().

🔗

template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator>(const duration<Rep1, Period1>& lhs,
                           const duration<Rep2, Period2>& rhs);

Returns: rhs < lhs.

🔗

template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator<=(const duration<Rep1, Period1>& lhs,
                            const duration<Rep2, Period2>& rhs);

Returns: !(rhs < lhs).

🔗

template<class Rep1, class Period1, class Rep2, class Period2>
  constexpr bool operator>=(const duration<Rep1, Period1>& lhs,
                            const duration<Rep2, Period2>& rhs);

Returns: !(lhs < rhs).

🔗

template<class Rep1, class Period1, class Rep2, class Period2>
  requires three_way_comparable<typename CT::rep>
  constexpr auto operator<=>(const duration<Rep1, Period1>& lhs,
                             const duration<Rep2, Period2>& rhs);

Returns: CT(lhs).count() <=> CT(rhs).count().

30.5.8 Conversions [time.duration.cast]

🔗

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

Constraints: ToDuration is a specialization of duration.

Returns: Let CF be ratio_divide<Period, typename ToDuration::period>, and CR be common_type<typename ToDuration::rep, Rep, intmax_t>::type.

(2.1)
If CF::num == 1 and CF::den == 1, returns ToDuration(static_cast<typename ToDuration::rep>(d.count()))
(2.2)
otherwise, if CF::num != 1 and CF::den == 1, returns ToDuration(static_cast<typename ToDuration::rep>( static_cast<CR>(d.count()) * static_cast<CR>(CF::num)))
(2.3)
otherwise, if CF::num == 1 and CF::den != 1, returns ToDuration(static_cast<typename ToDuration::rep>( static_cast<CR>(d.count()) / static_cast<CR>(CF::den)))
(2.4)
otherwise, returns ToDuration(static_cast<typename ToDuration::rep>( static_cast<CR>(d.count()) * static_cast<CR>(CF::num) / static_cast<CR>(CF::den)))

[Note 1:

This function does not use any implicit conversions; all conversions are done with static_cast.

It avoids multiplications and divisions when it is known at compile time that one or more arguments is 1.

Intermediate computations are carried out in the widest representation and only converted to the destination representation at the final step.

— end note]

🔗

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

Constraints: ToDuration is a specialization of duration.

Returns: The greatest result t representable in ToDuration for which t <= d.

🔗

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

Constraints: ToDuration is a specialization of duration.

Returns: The least result t representable in ToDuration for which t >= d.

🔗

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

Constraints: ToDuration is a specialization of duration and treat_as_floating_point_v<typename ToDuration::rep> is false.

Returns: The value of ToDuration that is closest to d.

If there are two closest values, then return the value t for which t % 2 == 0.

30.5.9 Suffixes for duration literals [time.duration.literals]

This subclause describes literal suffixes for constructing duration literals.

The suffixes h, min, s, ms, us, ns denote duration values of the corresponding types hours, minutes, seconds, milliseconds, microseconds, and nanoseconds respectively if they are applied to integer-literals.

If any of these suffixes are applied to a floating-point-literal the result is a chrono::duration literal with an unspecified floating-point representation.

If any of these suffixes are applied to an integer-literal and the resulting chrono::duration value cannot be represented in the result type because of overflow, the program is ill-formed.

[Example 1:

The following code shows some duration literals.

using namespace std::chrono_literals; auto constexpr aday=24h; auto constexpr lesson=45min; auto constexpr halfanhour=0.5h; — end example]

🔗

constexpr chrono::hours                                 operator""h(unsigned long long hours);
constexpr chrono::duration<unspecified, ratio<3600, 1>> operator""h(long double hours);

Returns: A duration literal representing hours hours.

🔗

constexpr chrono::minutes                             operator""min(unsigned long long minutes);
constexpr chrono::duration<unspecified, ratio<60, 1>> operator""min(long double minutes);

Returns: A duration literal representing minutes minutes.

🔗

constexpr chrono::seconds               operator""s(unsigned long long sec);
constexpr chrono::duration<unspecified> operator""s(long double sec);

Returns: A duration literal representing sec seconds.

[Note 1:

The same suffix s is used for basic_string but there is no conflict, since duration suffixes apply to numbers and string literal suffixes apply to character array literals.

— end note]

🔗

constexpr chrono::milliseconds                 operator""ms(unsigned long long msec);
constexpr chrono::duration<unspecified, milli> operator""ms(long double msec);

Returns: A duration literal representing msec milliseconds.

🔗

constexpr chrono::microseconds                 operator""us(unsigned long long usec);
constexpr chrono::duration<unspecified, micro> operator""us(long double usec);

Returns: A duration literal representing usec microseconds.

🔗

constexpr chrono::nanoseconds                 operator""ns(unsigned long long nsec);
constexpr chrono::duration<unspecified, nano> operator""ns(long double nsec);

Returns: A duration literal representing nsec nanoseconds.

30.5.10 Algorithms [time.duration.alg]

🔗

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

Constraints: numeric_limits<Rep>::is_signed is true.

Returns: If d >= d.zero(), return d, otherwise return -d.

30.5.11 I/O [time.duration.io]

🔗

template<class charT, class traits, class Rep, class Period>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const duration<Rep, Period>& d);

Effects: Inserts the duration d onto the stream os as if it were implemented as follows: basic_ostringstream<charT, traits> s; s.flags(os.flags()); s.imbue(os.getloc()); s.precision(os.precision()); s << d.count() << units-suffix; return os << s.str(); where units-suffix depends on the type Period::type as follows:

(1.1)
If Period::type is atto, units-suffix is "as".
(1.2)
Otherwise, if Period::type is femto, units-suffix is "fs".
(1.3)
Otherwise, if Period::type is pico, units-suffix is "ps".
(1.4)
Otherwise, if Period::type is nano, units-suffix is "ns".
(1.5)
Otherwise, if Period::type is micro, it is implementation-defined whether units-suffix is "μs" ("\u00b5\u0073") or "us".
(1.6)
Otherwise, if Period::type is milli, units-suffix is "ms".
(1.7)
Otherwise, if Period::type is centi, units-suffix is "cs".
(1.8)
Otherwise, if Period::type is deci, units-suffix is "ds".
(1.9)
Otherwise, if Period::type is ratio<1>, units-suffix is "s".
(1.10)
Otherwise, if Period::type is deca, units-suffix is "das".
(1.11)
Otherwise, if Period::type is hecto, units-suffix is "hs".
(1.12)
Otherwise, if Period::type is kilo, units-suffix is "ks".
(1.13)
Otherwise, if Period::type is mega, units-suffix is "Ms".
(1.14)
Otherwise, if Period::type is giga, units-suffix is "Gs".
(1.15)
Otherwise, if Period::type is tera, units-suffix is "Ts".
(1.16)
Otherwise, if Period::type is peta, units-suffix is "Ps".
(1.17)
Otherwise, if Period::type is exa, units-suffix is "Es".
(1.18)
Otherwise, if Period::type is ratio<60>, units-suffix is "min".
(1.19)
Otherwise, if Period::type is ratio<3600>, units-suffix is "h".
(1.20)
Otherwise, if Period::type is ratio<86400>, units-suffix is "d".
(1.21)
Otherwise, if Period::type::den == 1, units-suffix is "[num]s".
(1.22)
Otherwise, units-suffix is "[num/den]s".

In the list above, the use of num and den refers to the static data members of Period::type, which are converted to arrays of charT using a decimal conversion with no leading zeroes.

Returns: os.

🔗

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);

Effects: Attempts to parse the input stream is into the duration d using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid duration, is.setstate(ios_base::failbit) is called and d is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

30.6 Class template time_point [time.point]

30.6.1 General [time.point.general]

🔗

namespace std::chrono { template<class Clock, class Duration = typename Clock::duration> class time_point { public: using clock = Clock; using duration = Duration; using rep = typename duration::rep; using period = typename duration::period; private: duration d_; // exposition only public: // [time.point.cons], construct constexpr time_point(); // has value epoch constexpr explicit time_point(const duration& d); // same as time_point() + d template<class Duration2> constexpr time_point(const time_point<clock, Duration2>& t); // [time.point.observer], observer constexpr duration time_since_epoch() const; // [time.point.arithmetic], arithmetic constexpr time_point& operator++(); constexpr time_point operator++(int); constexpr time_point& operator--(); constexpr time_point operator--(int); constexpr time_point& operator+=(const duration& d); constexpr time_point& operator-=(const duration& d); // [time.point.special], special values static constexpr time_point min() noexcept; static constexpr time_point max() noexcept; }; }

If Duration is not a specialization of duration, the program is ill-formed.

30.6.2 Constructors [time.point.cons]

🔗

constexpr time_point();

Effects: Initializes d_ with duration::zero().

Such a time_point object represents the epoch.

🔗

constexpr explicit time_point(const duration& d);

Effects: Initializes d_ with d.

Such a time_point object represents the epoch + d.

🔗

template<class Duration2>
  constexpr time_point(const time_point<clock, Duration2>& t);

Constraints: is_convertible_v<Duration2, duration> is true.

Effects: Initializes d_ with t.time_since_epoch().

30.6.3 Observer [time.point.observer]

🔗

constexpr duration time_since_epoch() const;

Returns: d_.

30.6.4 Arithmetic [time.point.arithmetic]

🔗

constexpr time_point& operator++();

Effects: Equivalent to: ++d_.

Returns: *this.

🔗

constexpr time_point operator++(int);

Effects: Equivalent to: return time_point{d_++};

🔗

constexpr time_point& operator--();

Effects: Equivalent to: --d_.

Returns: *this.

🔗

constexpr time_point operator--(int);

Effects: Equivalent to: return time_point{d_--};

🔗

constexpr time_point& operator+=(const duration& d);

Effects: Equivalent to: d_ += d.

Returns: *this.

🔗

constexpr time_point& operator-=(const duration& d);

Effects: Equivalent to: d_ -= d.

Returns: *this.

30.6.5 Special values [time.point.special]

🔗

static constexpr time_point min() noexcept;

Returns: time_point(duration::min()).

🔗

static constexpr time_point max() noexcept;

Returns: time_point(duration::max()).

30.6.6 Non-member arithmetic [time.point.nonmember]

🔗

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);

Returns: CT(lhs.time_since_epoch() + rhs), where CT is the type of the return value.

🔗

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);

Returns: rhs + lhs.

🔗

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);

Returns: CT(lhs.time_since_epoch() - rhs), where CT is the type of the return value.

🔗

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);

Returns: lhs.time_since_epoch() - rhs.time_since_epoch().

30.6.7 Comparisons [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);

Returns: lhs.time_since_epoch() == rhs.time_since_epoch().

🔗

template<class Clock, class Duration1, class Duration2>
  constexpr bool operator<(const time_point<Clock, Duration1>& lhs,
                           const time_point<Clock, Duration2>& rhs);

Returns: lhs.time_since_epoch() < rhs.time_since_epoch().

🔗

template<class Clock, class Duration1, class Duration2>
  constexpr bool operator>(const time_point<Clock, Duration1>& lhs,
                           const time_point<Clock, Duration2>& rhs);

Returns: rhs < lhs.

🔗

template<class Clock, class Duration1, class Duration2>
  constexpr bool operator<=(const time_point<Clock, Duration1>& lhs,
                            const time_point<Clock, Duration2>& rhs);

Returns: !(rhs < lhs).

🔗

template<class Clock, class Duration1, class Duration2>
  constexpr bool operator>=(const time_point<Clock, Duration1>& lhs,
                            const time_point<Clock, Duration2>& rhs);

Returns: !(lhs < rhs).

🔗

template<class Clock, class Duration1,
         three_way_comparable_with<Duration1> Duration2>
  constexpr auto operator<=>(const time_point<Clock, Duration1>& lhs,
                             const time_point<Clock, Duration2>& rhs);

Returns: lhs.time_since_epoch() <=> rhs.time_since_epoch().

30.6.8 Conversions [time.point.cast]

🔗

template<class ToDuration, class Clock, class Duration>
  constexpr time_point<Clock, ToDuration> time_point_cast(const time_point<Clock, Duration>& t);

Constraints: ToDuration is a specialization of duration.

Returns: time_point<Clock, ToDuration>(duration_cast<ToDuration>(t.time_since_epoch()))

🔗

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

Constraints: ToDuration is a specialization of duration.

Returns: time_point<Clock, ToDuration>(floor<ToDuration>(tp.time_since_epoch())).

🔗

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

Constraints: ToDuration is a specialization of duration.

Returns: time_point<Clock, ToDuration>(ceil<ToDuration>(tp.time_since_epoch())).

🔗

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

Constraints: ToDuration is a specialization of duration, and treat_as_floating_point_v<typename ToDuration::rep> is false.

Returns: time_point<Clock, ToDuration>(round<ToDuration>(tp.time_since_epoch())).

30.7 Clocks [time.clock]

30.7.1 General [time.clock.general]

The types defined in [time.clock] meet the Cpp17TrivialClock requirements ([time.clock.req]) unless otherwise specified.

30.7.2 Class system_clock [time.clock.system]

30.7.2.1 Overview [time.clock.system.overview]

namespace std::chrono { class system_clock { public: using rep = see below; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<system_clock>; static constexpr bool is_steady = unspecified; static time_point now() noexcept; // mapping to/from C type time_t static time_t to_time_t (const time_point& t) noexcept; static time_point from_time_t(time_t t) noexcept; }; }

Objects of type system_clock represent wall clock time from the system-wide realtime clock.

Objects of type sys_time<Duration> measure time since 1970-01-01 00:00:00 UTC excluding leap seconds.

This measure is commonly referred to as Unix time.

This measure facilitates an efficient mapping between sys_time and calendar types ([time.cal]).

[Example 1:

sys_seconds{sys_days{1970y/January/1}}.time_since_epoch() is 0s.

sys_seconds{sys_days{2000y/January/1}}.time_since_epoch() is 946'684'800s, which is 10'957 * 86'400s.

— end example]

30.7.2.2 Members [time.clock.system.members]

🔗

using system_clock::rep = unspecified;

Constraints: system_clock::duration::min() < system_clock::duration::zero() is true.

[Note 1:

This implies that rep is a signed type.

— end note]

🔗

static time_t to_time_t(const time_point& t) noexcept;

Returns: A time_t object that represents the same point in time as t when both values are restricted to the coarser of the precisions of time_t and time_point.

It is implementation-defined whether values are rounded or truncated to the required precision.

🔗

static time_point from_time_t(time_t t) noexcept;

Returns: A time_point object that represents the same point in time as t when both values are restricted to the coarser of the precisions of time_t and time_point.

It is implementation-defined whether values are rounded or truncated to the required precision.

30.7.2.3 Non-member functions [time.clock.system.nonmembers]

🔗

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

Constraints: treat_as_floating_point_v<typename Duration::rep> is false, and Duration{1} < days{1} is true.

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%F %T}"), tp);

[Example 1: cout << sys_seconds{0s} << '\n'; // 1970-01-01 00:00:00 cout << sys_seconds{946'684'800s} << '\n'; // 2000-01-01 00:00:00 cout << sys_seconds{946'688'523s} << '\n'; // 2000-01-01 01:02:03 — end example]

🔗

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

Effects: os << year_month_day{dp}.

Returns: os.

🔗

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);

Effects: Attempts to parse the input stream is into the sys_time tp using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid date, is.setstate(ios_base::failbit) is called and tp is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Additionally, the parsed offset will be subtracted from the successfully parsed timestamp prior to assigning that difference to tp.

Returns: is.

30.7.3 Class utc_clock [time.clock.utc]

30.7.3.1 Overview [time.clock.utc.overview]

namespace std::chrono { class utc_clock { public: using rep = a signed arithmetic type; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<utc_clock>; static constexpr bool is_steady = unspecified; static time_point now(); template<class Duration> static sys_time<common_type_t<Duration, seconds>> to_sys(const utc_time<Duration>& t); template<class Duration> static utc_time<common_type_t<Duration, seconds>> from_sys(const sys_time<Duration>& t); }; }

In contrast to sys_time, which does not take leap seconds into account, utc_clock and its associated time_point, utc_time, count time, including leap seconds, since 1970-01-01 00:00:00 UTC.

[Note 1:

The UTC time standard began on 1972-01-01 00:00:10 TAI. To measure time since this epoch instead, one can add/subtract the constant sys_days{1972y/1/1} - sys_days{1970y/1/1} (63'072'000s) from the utc_time.

— end note]

[Example 1:

clock_cast<utc_clock>(sys_seconds{sys_days{1970y/January/1}}).time_since_epoch() is 0s.

clock_cast<utc_clock>(sys_seconds{sys_days{2000y/January/1}}).time_since_epoch() is 946'684'822s,

which is 10'957 * 86'400s + 22s.

— end example]

utc_clock is not a Cpp17TrivialClock unless the implementation can guarantee that utc_clock::now() does not propagate an exception.

[Note 2:

noexcept(from_sys(system_clock::now())) is false.

— end note]

30.7.3.2 Member functions [time.clock.utc.members]

🔗

static time_point now();

Returns: from_sys(system_clock::now()), or a more accurate value of utc_time.

🔗

template<class Duration>
  static sys_time<common_type_t<Duration, seconds>>
    to_sys(const utc_time<Duration>& u);

Returns: A sys_time t, such that from_sys(t) == u if such a mapping exists.

Otherwise u represents a time_point during a positive leap second insertion, the conversion counts that leap second as not inserted, and the last representable value of sys_time prior to the insertion of the leap second is returned.

🔗

template<class Duration>
  static utc_time<common_type_t<Duration, seconds>>
    from_sys(const sys_time<Duration>& t);

Returns: A utc_time u, such that u.time_since_epoch() - t.time_since_epoch() is equal to the sum of leap seconds that were inserted between t and 1970-01-01.

If t is exactly the date of leap second insertion, then the conversion counts that leap second as inserted.

[Example 1: auto t = sys_days{July/1/2015} - 2ns; auto u = utc_clock::from_sys(t); assert(u.time_since_epoch() - t.time_since_epoch() == 25s); t += 1ns; u = utc_clock::from_sys(t); assert(u.time_since_epoch() - t.time_since_epoch() == 25s); t += 1ns; u = utc_clock::from_sys(t); assert(u.time_since_epoch() - t.time_since_epoch() == 26s); t += 1ns; u = utc_clock::from_sys(t); assert(u.time_since_epoch() - t.time_since_epoch() == 26s); — end example]

30.7.3.3 Non-member functions [time.clock.utc.nonmembers]

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%F %T}"), t);

[Example 1: auto t = sys_days{July/1/2015} - 500ms; auto u = clock_cast<utc_clock>(t); for (auto i = 0; i < 8; ++i, u += 250ms) cout << u << " UTC\n";

Produces this output:

2015-06-30 23:59:59.500 UTC
2015-06-30 23:59:59.750 UTC
2015-06-30 23:59:60.000 UTC
2015-06-30 23:59:60.250 UTC
2015-06-30 23:59:60.500 UTC
2015-06-30 23:59:60.750 UTC
2015-07-01 00:00:00.000 UTC
2015-07-01 00:00:00.250 UTC

— end example]

🔗

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);

Effects: Attempts to parse the input stream is into the utc_time tp using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid date, is.setstate(ios_base::failbit) is called and tp is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Additionally, the parsed offset will be subtracted from the successfully parsed timestamp prior to assigning that difference to tp.

Returns: is.

🔗

struct leap_second_info {
  bool    is_leap_second;
  seconds elapsed;
};

The type leap_second_info has data members and special members specified above.

It has no base classes or members other than those specified.

🔗

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

Returns: A leap_second_info lsi, where lsi.is_leap_second is true if ut is during a positive leap second insertion, and otherwise false.

lsi.elapsed is the sum of leap seconds between 1970-01-01 and ut.

If lsi.is_leap_second is true, the leap second referred to by ut is included in the sum.

30.7.4 Class tai_clock [time.clock.tai]

30.7.4.1 Overview [time.clock.tai.overview]

namespace std::chrono { class tai_clock { public: using rep = a signed arithmetic type; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<tai_clock>; static constexpr bool is_steady = unspecified; static time_point now(); template<class Duration> static utc_time<common_type_t<Duration, seconds>> to_utc(const tai_time<Duration>&) noexcept; template<class Duration> static tai_time<common_type_t<Duration, seconds>> from_utc(const utc_time<Duration>&) noexcept; }; }

The clock tai_clock measures seconds since 1958-01-01 00:00:00 and is offset 10s ahead of UTC at this date.

That is, 1958-01-01 00:00:00 TAI is equivalent to 1957-12-31 23:59:50 UTC.

Leap seconds are not inserted into TAI.

Therefore every time a leap second is inserted into UTC, UTC shifts another second with respect to TAI.

For example by 2000-01-01 there had been 22 positive and 0 negative leap seconds inserted so 2000-01-01 00:00:00 UTC is equivalent to 2000-01-01 00:00:32 TAI (22s plus the initial 10s offset).

tai_clock is not a Cpp17TrivialClock unless the implementation can guarantee that tai_clock::now() does not propagate an exception.

[Note 1:

noexcept(from_utc(utc_clock::now())) is false.

— end note]

30.7.4.2 Member functions [time.clock.tai.members]

🔗

static time_point now();

Returns: from_utc(utc_clock::now()), or a more accurate value of tai_time.

🔗

template<class Duration>
  static utc_time<common_type_t<Duration, seconds>>
    to_utc(const tai_time<Duration>& t) noexcept;

Returns: utc_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} - 378691210s

[Note 1: 378691210s == sys_days{1970y/January/1} - sys_days{1958y/January/1} + 10s — end note]

🔗

template<class Duration>
  static tai_time<common_type_t<Duration, seconds>>
    from_utc(const utc_time<Duration>& t) noexcept;

Returns: tai_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} + 378691210s

[Note 2: 378691210s == sys_days{1970y/January/1} - sys_days{1958y/January/1} + 10s — end note]

30.7.4.3 Non-member functions [time.clock.tai.nonmembers]

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%F %T}"), t);

[Example 1: auto st = sys_days{2000y/January/1}; auto tt = clock_cast<tai_clock>(st); cout << format("{0:%F %T %Z} == {1:%F %T %Z}\n", st, tt);

Produces this output:

2000-01-01 00:00:00 UTC == 2000-01-01 00:00:32 TAI

— end example]

🔗

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);

Effects: Attempts to parse the input stream is into the tai_time tp using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid date, is.setstate(ios_base::failbit) is called and tp is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Additionally, the parsed offset will be subtracted from the successfully parsed timestamp prior to assigning that difference to tp.

Returns: is.

30.7.5 Class gps_clock [time.clock.gps]

30.7.5.1 Overview [time.clock.gps.overview]

namespace std::chrono { class gps_clock { public: using rep = a signed arithmetic type; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<gps_clock>; static constexpr bool is_steady = unspecified; static time_point now(); template<class Duration> static utc_time<common_type_t<Duration, seconds>> to_utc(const gps_time<Duration>&) noexcept; template<class Duration> static gps_time<common_type_t<Duration, seconds>> from_utc(const utc_time<Duration>&) noexcept; }; }

The clock gps_clock measures seconds since the first Sunday of January, 1980 00:00:00 UTC.

Leap seconds are not inserted into GPS.

Therefore every time a leap second is inserted into UTC, UTC shifts another second with respect to GPS.

Aside from the offset from 1958y/January/1 to 1980y/January/Sunday[1], GPS is behind TAI by 19s due to the 10s offset between 1958 and 1970 and the additional 9 leap seconds inserted between 1970 and 1980.

gps_clock is not a Cpp17TrivialClock unless the implementation can guarantee that gps_clock::now() does not propagate an exception.

[Note 1:

noexcept(from_utc(utc_clock::now())) is false.

— end note]

30.7.5.2 Member functions [time.clock.gps.members]

🔗

static time_point now();

Returns: from_utc(utc_clock::now()), or a more accurate value of gps_time.

🔗

template<class Duration>
  static utc_time<common_type_t<Duration, seconds>>
    to_utc(const gps_time<Duration>& t) noexcept;

Returns: utc_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} + 315964809s

[Note 1: 315964809s == sys_days{1980y/January/Sunday[1]} - sys_days{1970y/January/1} + 9s — end note]

🔗

template<class Duration>
  static gps_time<common_type_t<Duration, seconds>>
    from_utc(const utc_time<Duration>& t) noexcept;

Returns: gps_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} - 315964809s

[Note 2: 315964809s == sys_days{1980y/January/Sunday[1]} - sys_days{1970y/January/1} + 9s — end note]

30.7.5.3 Non-member functions [time.clock.gps.nonmembers]

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%F %T}"), t);

[Example 1: auto st = sys_days{2000y/January/1}; auto gt = clock_cast<gps_clock>(st); cout << format("{0:%F %T %Z} == {1:%F %T %Z}\n", st, gt);

Produces this output:

2000-01-01 00:00:00 UTC == 2000-01-01 00:00:13 GPS

— end example]

🔗

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);

Effects: Attempts to parse the input stream is into the gps_time tp using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid date, is.setstate(ios_base::failbit) is called and tp is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Additionally, the parsed offset will be subtracted from the successfully parsed timestamp prior to assigning that difference to tp.

Returns: is.

30.7.6 Type file_clock [time.clock.file]

30.7.6.1 Overview [time.clock.file.overview]

namespace std::chrono { using file_clock = see below; }

file_clock is an alias for a type meeting the Cpp17TrivialClock requirements ([time.clock.req]), and using a signed arithmetic type for file_clock::rep.

file_clock is used to create the time_point system used for file_time_type ([filesystems]).

Its epoch is unspecified, and noexcept(file_clock::now()) is true.

[Note 1:

The type that file_clock denotes can be in a different namespace than std::chrono, such as std::filesystem.

— end note]

30.7.6.2 Member functions [time.clock.file.members]

The type denoted by file_clock provides precisely one of the following two sets of static member functions: template<class Duration> static sys_time<see below> to_sys(const file_time<Duration>&); template<class Duration> static file_time<see below> from_sys(const sys_time<Duration>&); or: template<class Duration> static utc_time<see below> to_utc(const file_time<Duration>&); template<class Duration> static file_time<see below> from_utc(const utc_time<Duration>&);

These member functions shall provide time_point conversions consistent with those specified by utc_clock, tai_clock, and gps_clock.

The Duration of the resultant time_point is computed from the Duration of the input time_point.

30.7.6.3 Non-member functions [time.clock.file.nonmembers]

🔗

template<class charT, class traits, class Duration>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const file_time<Duration>& t);

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%F %T}"), 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,
                file_time<Duration>& tp, basic_string<charT, traits, Alloc>* abbrev = nullptr,
                minutes* offset = nullptr);

Effects: Attempts to parse the input stream is into the file_time tp using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid date, is.setstate(ios_base::failbit) is called and tp is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Additionally, the parsed offset will be subtracted from the successfully parsed timestamp prior to assigning that difference to tp.

Returns: is.

30.7.7 Class steady_clock [time.clock.steady]

namespace std::chrono { class steady_clock { public: using rep = unspecified; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<unspecified, duration>; static constexpr bool is_steady = true; static time_point now() noexcept; }; }

Objects of class steady_clock represent clocks for which values of time_point never decrease as physical time advances and for which values of time_point advance at a steady rate relative to real time.

That is, the clock may not be adjusted.

30.7.8 Class high_resolution_clock [time.clock.hires]

namespace std::chrono { class high_resolution_clock { public: using rep = unspecified; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<unspecified, duration>; static constexpr bool is_steady = unspecified; static time_point now() noexcept; }; }

Objects of class high_resolution_clock represent clocks with the shortest tick period.

high_resolution_clock may be a synonym for system_clock or steady_clock.

30.7.9 Local time [time.clock.local]

The family of time points denoted by local_time<Duration> are based on the pseudo clock local_t.

local_t has no member now() and thus does not meet the clock requirements.

Nevertheless local_time<Duration> serves the vital role of representing local time with respect to a not-yet-specified time zone.

Aside from being able to get the current time, the complete time_point algebra is available for local_time<Duration> (just as for sys_time<Duration>).

🔗

template<class charT, class traits, class Duration>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os, const local_time<Duration>& lt);

Effects: os << sys_time<Duration>{lt.time_since_epoch()};

Returns: os.

🔗

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);

Effects: Attempts to parse the input stream is into the local_time tp using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid date, is.setstate(ios_base::failbit) is called and tp is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

30.7.10 time_point conversions [time.clock.cast]

30.7.10.1 Class template clock_time_conversion [time.clock.conv]

namespace std::chrono { template<class DestClock, class SourceClock> struct clock_time_conversion {}; }

clock_time_conversion serves as a trait which can be used to specify how to convert a source time_point of type time_point<SourceClock, Duration> to a destination time_point of type time_point<DestClock, Duration> via a specialization: clock_time_conversion<DestClock, SourceClock>.

A specialization of clock_time_conversion<DestClock, SourceClock> shall provide a const-qualified operator() that takes a parameter of type time_point<SourceClock, Duration> and returns a time_point<DestClock, OtherDuration> representing an equivalent point in time.

OtherDuration is a chrono::duration whose specialization is computed from the input Duration in a manner which can vary for each clock_time_conversion specialization.

A program may specialize clock_time_conversion if at least one of the template parameters is a user-defined clock type.

Several specializations are provided by the implementation, as described in [time.clock.cast.id], [time.clock.cast.sys.utc], [time.clock.cast.sys], and [time.clock.cast.utc].

30.7.10.2 Identity conversions [time.clock.cast.id]

template<class Clock> struct clock_time_conversion<Clock, Clock> { template<class Duration> time_point<Clock, Duration> operator()(const time_point<Clock, Duration>& t) const; };

🔗

template<class Duration>
  time_point<Clock, Duration>
    operator()(const time_point<Clock, Duration>& t) const;

Returns: t.

template<> struct clock_time_conversion<system_clock, system_clock> { template<class Duration> sys_time<Duration> operator()(const sys_time<Duration>& t) const; };

🔗

template<class Duration>
  sys_time<Duration>
    operator()(const sys_time<Duration>& t) const;

Returns: t.

template<> struct clock_time_conversion<utc_clock, utc_clock> { template<class Duration> utc_time<Duration> operator()(const utc_time<Duration>& t) const; };

🔗

template<class Duration>
  utc_time<Duration>
    operator()(const utc_time<Duration>& t) const;

Returns: t.

30.7.10.3 Conversions between system_clock and utc_clock [time.clock.cast.sys.utc]

template<> struct clock_time_conversion<utc_clock, system_clock> { template<class Duration> utc_time<common_type_t<Duration, seconds>> operator()(const sys_time<Duration>& t) const; };

🔗

template<class Duration>
  utc_time<common_type_t<Duration, seconds>>
    operator()(const sys_time<Duration>& t) const;

Returns: utc_clock::from_sys(t).

template<> struct clock_time_conversion<system_clock, utc_clock> { template<class Duration> sys_time<common_type_t<Duration, seconds>> operator()(const utc_time<Duration>& t) const; };

🔗

template<class Duration>
  sys_time<common_type_t<Duration, seconds>>
    operator()(const utc_time<Duration>& t) const;

Returns: utc_clock::to_sys(t).

30.7.10.4 Conversions between system_clock and other clocks [time.clock.cast.sys]

template<class SourceClock> struct clock_time_conversion<system_clock, SourceClock> { template<class Duration> auto operator()(const time_point<SourceClock, Duration>& t) const -> decltype(SourceClock::to_sys(t)); };

🔗

template<class Duration>
  auto operator()(const time_point<SourceClock, Duration>& t) const
    -> decltype(SourceClock::to_sys(t));

Constraints: SourceClock::to_sys(t) is well-formed.

Mandates: SourceClock::to_sys(t) returns a sys_time<Duration2> for some type Duration2 ([time.point.general]).

Returns: SourceClock::to_sys(t).

template<class DestClock> struct clock_time_conversion<DestClock, system_clock> { template<class Duration> auto operator()(const sys_time<Duration>& t) const -> decltype(DestClock::from_sys(t)); };

🔗

template<class Duration>
  auto operator()(const sys_time<Duration>& t) const
    -> decltype(DestClock::from_sys(t));

Constraints: DestClock::from_sys(t) is well-formed.

Mandates: DestClock::from_sys(t) returns a time_point<DestClock, Duration2> for some type Duration2 ([time.point.general]).

Returns: DestClock::from_sys(t).

30.7.10.5 Conversions between utc_clock and other clocks [time.clock.cast.utc]

template<class SourceClock> struct clock_time_conversion<utc_clock, SourceClock> { template<class Duration> auto operator()(const time_point<SourceClock, Duration>& t) const -> decltype(SourceClock::to_utc(t)); };

🔗

template<class Duration>
  auto operator()(const time_point<SourceClock, Duration>& t) const
    -> decltype(SourceClock::to_utc(t));

Constraints: SourceClock::to_utc(t) is well-formed.

Mandates: SourceClock::to_utc(t) returns a utc_time<Duration2> for some type Duration2 ([time.point.general]).

Returns: SourceClock::to_utc(t).

template<class DestClock> struct clock_time_conversion<DestClock, utc_clock> { template<class Duration> auto operator()(const utc_time<Duration>& t) const -> decltype(DestClock::from_utc(t)); };

🔗

template<class Duration>
  auto operator()(const utc_time<Duration>& t) const
    -> decltype(DestClock::from_utc(t));

Constraints: DestClock::from_utc(t) is well-formed.

Mandates: DestClock::from_utc(t) returns a time_point<DestClock, Duration2> for some type Duration2 ([time.point.general]).

Returns: DestClock::from_utc(t).

30.7.10.6 Function template clock_cast [time.clock.cast.fn]

🔗

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

Constraints: At least one of the following clock time conversion expressions is well-formed:

(1.1)
clock_time_conversion<DestClock, SourceClock>{}(t)
(1.2)
clock_time_conversion<DestClock, system_clock>{}( clock_time_conversion<system_clock, SourceClock>{}(t))
(1.3)
clock_time_conversion<DestClock, utc_clock>{}( clock_time_conversion<utc_clock, SourceClock>{}(t))
(1.4)
clock_time_conversion<DestClock, utc_clock>{}( clock_time_conversion<utc_clock, system_clock>{}( clock_time_conversion<system_clock, SourceClock>{}(t)))
(1.5)
clock_time_conversion<DestClock, system_clock>{}( clock_time_conversion<system_clock, utc_clock>{}( clock_time_conversion<utc_clock, SourceClock>{}(t)))

A clock time conversion expression is considered better than another clock time conversion expression if it involves fewer operator() calls on clock_time_conversion specializations.

Mandates: Among the well-formed clock time conversion expressions from the above list, there is a unique best expression.

Returns: The best well-formed clock time conversion expression in the above list.

30.8 The civil calendar [time.cal]

30.8.1 General [time.cal.general]

The types in [time.cal] describe the civil (Gregorian) calendar and its relationship to sys_days and local_days.

30.8.2 Class last_spec [time.cal.last]

namespace std::chrono { struct last_spec { explicit last_spec() = default; }; }

The type last_spec is used in conjunction with other calendar types to specify the last in a sequence.

For example, depending on context, it can represent the last day of a month, or the last day of the week of a month.

30.8.3 Class day [time.cal.day]

30.8.3.1 Overview [time.cal.day.overview]

namespace std::chrono { class day { unsigned char d_; // exposition only public: day() = default; constexpr explicit day(unsigned d) noexcept; constexpr day& operator++() noexcept; constexpr day operator++(int) noexcept; constexpr day& operator--() noexcept; constexpr day operator--(int) noexcept; constexpr day& operator+=(const days& d) noexcept; constexpr day& operator-=(const days& d) noexcept; constexpr explicit operator unsigned() const noexcept; constexpr bool ok() const noexcept; }; }

day represents a day of a month.

It normally holds values in the range 1 to 31, but may hold non-negative values outside this range.

It can be constructed with any unsigned value, which will be subsequently truncated to fit into day's unspecified internal storage.

day meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements, and participates in basic arithmetic with days objects, which represent a difference between two day objects.

day is a trivially copyable and standard-layout class type.

30.8.3.2 Member functions [time.cal.day.members]

🔗

constexpr explicit day(unsigned d) noexcept;

Effects: Initializes d_ with d.

The value held is unspecified if d is not in the range [0, 255].

🔗

constexpr day& operator++() noexcept;

Effects: ++d_.

Returns: *this.

🔗

constexpr day operator++(int) noexcept;

Effects: ++(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

constexpr day& operator--() noexcept;

Effects: Equivalent to: --d_.

Returns: *this.

🔗

constexpr day operator--(int) noexcept;

Effects: --(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

constexpr day& operator+=(const days& d) noexcept;

Effects: *this = *this + d.

Returns: *this.

🔗

constexpr day& operator-=(const days& d) noexcept;

Effects: *this = *this - d.

Returns: *this.

🔗

constexpr explicit operator unsigned() const noexcept;

Returns: d_.

🔗

constexpr bool ok() const noexcept;

Returns: 1 <= d_ && d_ <= 31.

30.8.3.3 Non-member functions [time.cal.day.nonmembers]

🔗

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

Returns: unsigned{x} == unsigned{y}.

🔗

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

Returns: unsigned{x} <=> unsigned{y}.

🔗

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

Returns: day(unsigned{x} + y.count()).

🔗

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

Returns: y + x.

🔗

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

Returns: x + -y.

🔗

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

Returns: days{int(unsigned{x}) - int(unsigned{y})}.

🔗

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

Effects: Equivalent to: return os << (d.ok() ? format(STATICALLY-WIDEN<charT>("{:%d}"), d) : format(STATICALLY-WIDEN<charT>("{:%d} is not a valid 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);

Effects: Attempts to parse the input stream is into the day d using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid day, is.setstate(ios_base::failbit) is called and d is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

🔗

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

Returns: day{static_cast<unsigned>(d)}.

30.8.4 Class month [time.cal.month]

30.8.4.1 Overview [time.cal.month.overview]

namespace std::chrono { class month { unsigned char m_; // exposition only public: month() = default; constexpr explicit month(unsigned m) noexcept; constexpr month& operator++() noexcept; constexpr month operator++(int) noexcept; constexpr month& operator--() noexcept; constexpr month operator--(int) noexcept; constexpr month& operator+=(const months& m) noexcept; constexpr month& operator-=(const months& m) noexcept; constexpr explicit operator unsigned() const noexcept; constexpr bool ok() const noexcept; }; }

month represents a month of a year.

It normally holds values in the range 1 to 12, but may hold non-negative values outside this range.

It can be constructed with any unsigned value, which will be subsequently truncated to fit into month's unspecified internal storage.

month meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements, and participates in basic arithmetic with months objects, which represent a difference between two month objects.

month is a trivially copyable and standard-layout class type.

30.8.4.2 Member functions [time.cal.month.members]

🔗

constexpr explicit month(unsigned m) noexcept;

Effects: Initializes m_ with m.

The value held is unspecified if m is not in the range [0, 255].

🔗

constexpr month& operator++() noexcept;

Effects: *this += months{1}.

Returns: *this.

🔗

constexpr month operator++(int) noexcept;

Effects: ++(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

constexpr month& operator--() noexcept;

Effects: *this -= months{1}.

Returns: *this.

🔗

constexpr month operator--(int) noexcept;

Effects: --(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

constexpr month& operator+=(const months& m) noexcept;

Effects: *this = *this + m.

Returns: *this.

🔗

constexpr month& operator-=(const months& m) noexcept;

Effects: *this = *this - m.

Returns: *this.

🔗

constexpr explicit operator unsigned() const noexcept;

Returns: m_.

🔗

constexpr bool ok() const noexcept;

Returns: 1 <= m_ && m_ <= 12.

30.8.4.3 Non-member functions [time.cal.month.nonmembers]

🔗

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

Returns: unsigned{x} == unsigned{y}.

🔗

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

Returns: unsigned{x} <=> unsigned{y}.

🔗

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

Returns: month{modulo(static_cast<long long>(unsigned{x}) + (y.count() - 1), 12) + 1} where modulo(n, 12) computes the remainder of n divided by 12 using Euclidean division.

[Note 1:

Given a divisor of 12, Euclidean division truncates towards negative infinity and always produces a remainder in the range of [0, 11].

Assuming no overflow in the signed summation, this operation results in a month holding a value in the range [1, 12] even if !x.ok().

— end note]

[Example 1:

February + months{11} == January.

— end example]

🔗

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

Returns: y + x.

🔗

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

Returns: x + -y.

🔗

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

Returns: If x.ok() == true and y.ok() == true, returns a value m in the range [months{0}, months{11}] satisfying y + m == x.

Otherwise the value returned is unspecified.

[Example 2:

January - February == months{11}.

— end example]

🔗

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

Effects: Equivalent to: return os << (m.ok() ? format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%b}"), m) : format(os.getloc(), STATICALLY-WIDEN<charT>("{} is not a valid month"), static_cast<unsigned>(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);

Effects: Attempts to parse the input stream is into the month m using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid month, is.setstate(ios_base::failbit) is called and m is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

30.8.5 Class year [time.cal.year]

30.8.5.1 Overview [time.cal.year.overview]

namespace std::chrono { class year { short y_; // exposition only public: year() = default; constexpr explicit year(int y) noexcept; constexpr year& operator++() noexcept; constexpr year operator++(int) noexcept; constexpr year& operator--() noexcept; constexpr year operator--(int) noexcept; constexpr year& operator+=(const years& y) noexcept; constexpr year& operator-=(const years& y) noexcept; constexpr year operator+() const noexcept; constexpr year operator-() const noexcept; constexpr bool is_leap() const noexcept; constexpr explicit operator int() const noexcept; constexpr bool ok() const noexcept; static constexpr year min() noexcept; static constexpr year max() noexcept; }; }

year represents a year in the civil calendar.

It can represent values in the range [min(), max()].

It can be constructed with any int value, which will be subsequently truncated to fit into year's unspecified internal storage.

year meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements, and participates in basic arithmetic with years objects, which represent a difference between two year objects.

year is a trivially copyable and standard-layout class type.

30.8.5.2 Member functions [time.cal.year.members]

🔗

constexpr explicit year(int y) noexcept;

Effects: Initializes y_ with y.

The value held is unspecified if y is not in the range [-32767, 32767].

🔗

constexpr year& operator++() noexcept;

Effects: ++y_.

Returns: *this.

🔗

constexpr year operator++(int) noexcept;

Effects: ++(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

constexpr year& operator--() noexcept;

Effects: --y_.

Returns: *this.

🔗

constexpr year operator--(int) noexcept;

Effects: --(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

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

Effects: *this = *this + y.

Returns: *this.

🔗

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

Effects: *this = *this - y.

Returns: *this.

🔗

constexpr year operator+() const noexcept;

Returns: *this.

🔗

constexpr year operator-() const noexcept;

Returns: year{-y_}.

🔗

constexpr bool is_leap() const noexcept;

Returns: y_ % 4 == 0 && (y_ % 100 != 0 || y_ % 400 == 0).

🔗

constexpr explicit operator int() const noexcept;

Returns: y_.

🔗

constexpr bool ok() const noexcept;

Returns: min().y_ <= y_ && y_ <= max().y_.

🔗

static constexpr year min() noexcept;

Returns: year{-32767}.

🔗

static constexpr year max() noexcept;

Returns: year{32767}.

30.8.5.3 Non-member functions [time.cal.year.nonmembers]

🔗

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

Returns: int{x} == int{y}.

🔗

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

Returns: int{x} <=> int{y}.

🔗

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

Returns: year{int{x} + static_cast<int>(y.count())}.

🔗

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

Returns: y + x.

🔗

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

Returns: x + -y.

🔗

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

Returns: years{int{x} - int{y}}.

🔗

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

Effects: Equivalent to: return os << (y.ok() ? format(STATICALLY-WIDEN<charT>("{:%Y}"), y) : format(STATICALLY-WIDEN<charT>("{:%Y} is not a valid 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);

Effects: Attempts to parse the input stream is into the year y using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid year, is.setstate(ios_base::failbit) is called and y is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

🔗

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

Returns: year{static_cast<int>(y)}.

30.8.6 Class weekday [time.cal.wd]

30.8.6.1 Overview [time.cal.wd.overview]

namespace std::chrono { class weekday { unsigned char wd_; // exposition only public: weekday() = default; constexpr explicit weekday(unsigned wd) noexcept; constexpr weekday(const sys_days& dp) noexcept; constexpr explicit weekday(const local_days& dp) noexcept; constexpr weekday& operator++() noexcept; constexpr weekday operator++(int) noexcept; constexpr weekday& operator--() noexcept; constexpr weekday operator--(int) noexcept; constexpr weekday& operator+=(const days& d) noexcept; constexpr weekday& operator-=(const days& d) noexcept; constexpr unsigned c_encoding() const noexcept; constexpr unsigned iso_encoding() const noexcept; constexpr bool ok() const noexcept; constexpr weekday_indexed operator[](unsigned index) const noexcept; constexpr weekday_last operator[](last_spec) const noexcept; }; }

weekday represents a day of the week in the civil calendar.

It normally holds values in the range 0 to 6, corresponding to Sunday through Saturday, but it may hold non-negative values outside this range.

It can be constructed with any unsigned value, which will be subsequently truncated to fit into weekday's unspecified internal storage.

weekday meets the Cpp17EqualityComparable (Table 28) requirements.

[Note 1:

weekday is not Cpp17LessThanComparable because there is no universal consensus on which day is the first day of the week.

weekday's arithmetic operations treat the days of the week as a circular range, with no beginning and no end.

— end note]

weekday is a trivially copyable and standard-layout class type.

30.8.6.2 Member functions [time.cal.wd.members]

🔗

constexpr explicit weekday(unsigned wd) noexcept;

Effects: Initializes wd_ with wd == 7 ? 0 : wd.

The value held is unspecified if wd is not in the range [0, 255].

🔗

constexpr weekday(const sys_days& dp) noexcept;

Effects: Computes what day of the week corresponds to the sys_days dp, and initializes that day of the week in wd_.

[Example 1:

If dp represents 1970-01-01, the constructed weekday represents Thursday by storing 4 in wd_.

— end example]

🔗

constexpr explicit weekday(const local_days& dp) noexcept;

Effects: Computes what day of the week corresponds to the local_days dp, and initializes that day of the week in wd_.

Postconditions: The value is identical to that constructed from sys_days{dp.time_since_epoch()}.

🔗

constexpr weekday& operator++() noexcept;

Effects: *this += days{1}.

Returns: *this.

🔗

constexpr weekday operator++(int) noexcept;

Effects: ++(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

constexpr weekday& operator--() noexcept;

Effects: *this -= days{1}.

Returns: *this.

🔗

constexpr weekday operator--(int) noexcept;

Effects: --(*this).

Returns: A copy of *this as it existed on entry to this member function.

🔗

constexpr weekday& operator+=(const days& d) noexcept;

Effects: *this = *this + d.

Returns: *this.

🔗

constexpr weekday& operator-=(const days& d) noexcept;

Effects: *this = *this - d.

Returns: *this.

🔗

constexpr unsigned c_encoding() const noexcept;

Returns: wd_.

🔗

constexpr unsigned iso_encoding() const noexcept;

Returns: wd_ == 0u ? 7u : wd_.

🔗

constexpr bool ok() const noexcept;

Returns: wd_ <= 6.

🔗

constexpr weekday_indexed operator[](unsigned index) const noexcept;

Returns: {*this, index}.

🔗

constexpr weekday_last operator[](last_spec) const noexcept;

Returns: weekday_last{*this}.

30.8.6.3 Non-member functions [time.cal.wd.nonmembers]

🔗

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

Returns: x.wd_ == y.wd_.

🔗

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

Returns: weekday{modulo(static_cast<long long>(x.wd_) + y.count(), 7)} where modulo(n, 7) computes the remainder of n divided by 7 using Euclidean division.

[Note 1:

Given a divisor of 7, Euclidean division truncates towards negative infinity and always produces a remainder in the range of [0, 6].

Assuming no overflow in the signed summation, this operation results in a weekday holding a value in the range [0, 6] even if !x.ok().

— end note]

[Example 1:

Monday + days{6} == Sunday.

— end example]

🔗

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

Returns: y + x.

🔗

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

Returns: x + -y.

🔗

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

Returns: If x.ok() == true and y.ok() == true, returns a value d in the range [days{0}, days{6}] satisfying y + d == x.

Otherwise the value returned is unspecified.

[Example 2:

Sunday - Monday == days{6}.

— end example]

🔗

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

Effects: Equivalent to: return os << (wd.ok() ? format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%a}"), wd) : format(os.getloc(), STATICALLY-WIDEN<charT>("{} is not a valid weekday"), static_cast<unsigned>(wd.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);

Effects: Attempts to parse the input stream is into the weekday wd using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid weekday, is.setstate(ios_base::failbit) is called and wd is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

30.8.7 Class weekday_indexed [time.cal.wdidx]

30.8.7.1 Overview [time.cal.wdidx.overview]

namespace std::chrono { class weekday_indexed { chrono::weekday wd_; // exposition only unsigned char index_; // exposition only public: weekday_indexed() = default; constexpr weekday_indexed(const chrono::weekday& wd, unsigned index) noexcept; constexpr chrono::weekday weekday() const noexcept; constexpr unsigned index() const noexcept; constexpr bool ok() const noexcept; }; }

weekday_indexed represents a weekday and a small index in the range 1 to 5.

This class is used to represent the first, second, third, fourth, or fifth weekday of a month.

[Note 1:

A weekday_indexed object can be constructed by indexing a weekday with an unsigned.

— end note]

[Example 1: constexpr auto wdi = Sunday[2]; // wdi is the second Sunday of an as yet unspecified month static_assert(wdi.weekday() == Sunday); static_assert(wdi.index() == 2); — end example]

weekday_indexed is a trivially copyable and standard-layout class type.

30.8.7.2 Member functions [time.cal.wdidx.members]

🔗

constexpr weekday_indexed(const chrono::weekday& wd, unsigned index) noexcept;

Effects: Initializes wd_ with wd and index_ with index.

The values held are unspecified if !wd.ok() or index is not in the range [0, 7].

🔗

constexpr chrono::weekday weekday() const noexcept;

Returns: wd_.

🔗

constexpr unsigned index() const noexcept;

Returns: index_.

🔗

constexpr bool ok() const noexcept;

Returns: wd_.ok() && 1 <= index_ && index_ <= 5.

30.8.7.3 Non-member functions [time.cal.wdidx.nonmembers]

🔗

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

Returns: x.weekday() == y.weekday() && x.index() == y.index().

🔗

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

Effects: Equivalent to: auto i = wdi.index(); return os << (i >= 1 && i <= 5 ? format(os.getloc(), STATICALLY-WIDEN<charT>("{:L}[{}]"), wdi.weekday(), i) : format(os.getloc(), STATICALLY-WIDEN<charT>("{:L}[{} is not a valid index]"), wdi.weekday(), i));

30.8.8 Class weekday_last [time.cal.wdlast]

30.8.8.1 Overview [time.cal.wdlast.overview]

namespace std::chrono { class weekday_last { chrono::weekday wd_; // exposition only public: constexpr explicit weekday_last(const chrono::weekday& wd) noexcept; constexpr chrono::weekday weekday() const noexcept; constexpr bool ok() const noexcept; }; }

weekday_last represents the last weekday of a month.

[Note 1:

A weekday_last object can be constructed by indexing a weekday with last.

— end note]

[Example 1: constexpr auto wdl = Sunday[last]; // wdl is the last Sunday of an as yet unspecified month static_assert(wdl.weekday() == Sunday); — end example]

weekday_last is a trivially copyable and standard-layout class type.

30.8.8.2 Member functions [time.cal.wdlast.members]

🔗

constexpr explicit weekday_last(const chrono::weekday& wd) noexcept;

Effects: Initializes wd_ with wd.

🔗

constexpr chrono::weekday weekday() const noexcept;

Returns: wd_.

🔗

constexpr bool ok() const noexcept;

Returns: wd_.ok().

30.8.8.3 Non-member functions [time.cal.wdlast.nonmembers]

🔗

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

Returns: x.weekday() == y.weekday().

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L}[last]"), wdl.weekday());

30.8.9 Class month_day [time.cal.md]

30.8.9.1 Overview [time.cal.md.overview]

namespace std::chrono { class month_day { chrono::month m_; // exposition only chrono::day d_; // exposition only public: month_day() = default; constexpr month_day(const chrono::month& m, const chrono::day& d) noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::day day() const noexcept; constexpr bool ok() const noexcept; }; }

month_day represents a specific day of a specific month, but with an unspecified year.

month_day meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements.

month_day is a trivially copyable and standard-layout class type.

30.8.9.2 Member functions [time.cal.md.members]

🔗

constexpr month_day(const chrono::month& m, const chrono::day& d) noexcept;

Effects: Initializes m_ with m, and d_ with d.

🔗

constexpr chrono::month month() const noexcept;

Returns: m_.

🔗

constexpr chrono::day day() const noexcept;

Returns: d_.

🔗

constexpr bool ok() const noexcept;

Returns: true if m_.ok() is true, 1d <= d_, and d_ is less than or equal to the number of days in month m_; otherwise returns false.

When m_ == February, the number of days is considered to be 29.

30.8.9.3 Non-member functions [time.cal.md.nonmembers]

🔗

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

Returns: x.month() == y.month() && x.day() == y.day().

🔗

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

Effects: Equivalent to: if (auto c = x.month() <=> y.month(); c != 0) return c; return x.day() <=> y.day();

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L}/{}"), md.month(), md.day());

🔗

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);

Effects: Attempts to parse the input stream is into the month_day md using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid month_day, is.setstate(ios_base::failbit) is called and md is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

30.8.10 Class month_day_last [time.cal.mdlast]

namespace std::chrono { class month_day_last { chrono::month m_; // exposition only public: constexpr explicit month_day_last(const chrono::month& m) noexcept; constexpr chrono::month month() const noexcept; constexpr bool ok() const noexcept; }; }

month_day_last represents the last day of a month.

[Note 1:

A month_day_last object can be constructed using the expression m/last or last/m, where m is an expression of type month.

— end note]

[Example 1: constexpr auto mdl = February/last; // mdl is the last day of February of an as yet unspecified year static_assert(mdl.month() == February); — end example]

month_day_last is a trivially copyable and standard-layout class type.

🔗

constexpr explicit month_day_last(const chrono::month& m) noexcept;

Effects: Initializes m_ with m.

🔗

constexpr month month() const noexcept;

Returns: m_.

🔗

constexpr bool ok() const noexcept;

Returns: m_.ok().

🔗

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

Returns: x.month() == y.month().

🔗

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

Returns: x.month() <=> y.month().

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L}/last"), mdl.month());

30.8.11 Class month_weekday [time.cal.mwd]

30.8.11.1 Overview [time.cal.mwd.overview]

namespace std::chrono { class month_weekday { chrono::month m_; // exposition only chrono::weekday_indexed wdi_; // exposition only public: constexpr month_weekday(const chrono::month& m, const chrono::weekday_indexed& wdi) noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::weekday_indexed weekday_indexed() const noexcept; constexpr bool ok() const noexcept; }; }

month_weekday represents the

n^{th}

weekday of a month, of an as yet unspecified year.

To do this the month_weekday stores a month and a weekday_indexed.

[Example 1: constexpr auto mwd = February/Tuesday[3]; // mwd is the third Tuesday of February of an as yet unspecified year static_assert(mwd.month() == February); static_assert(mwd.weekday_indexed() == Tuesday[3]); — end example]

month_weekday is a trivially copyable and standard-layout class type.

30.8.11.2 Member functions [time.cal.mwd.members]

🔗

constexpr month_weekday(const chrono::month& m, const chrono::weekday_indexed& wdi) noexcept;

Effects: Initializes m_ with m, and wdi_ with wdi.

🔗

constexpr chrono::month month() const noexcept;

Returns: m_.

🔗

constexpr chrono::weekday_indexed weekday_indexed() const noexcept;

Returns: wdi_.

🔗

constexpr bool ok() const noexcept;

Returns: m_.ok() && wdi_.ok().

30.8.11.3 Non-member functions [time.cal.mwd.nonmembers]

🔗

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

Returns: x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed().

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L}/{:L}"), mwd.month(), mwd.weekday_indexed());

30.8.12 Class month_weekday_last [time.cal.mwdlast]

30.8.12.1 Overview [time.cal.mwdlast.overview]

namespace std::chrono { class month_weekday_last { chrono::month m_; // exposition only chrono::weekday_last wdl_; // exposition only public: constexpr month_weekday_last(const chrono::month& m, const chrono::weekday_last& wdl) noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::weekday_last weekday_last() const noexcept; constexpr bool ok() const noexcept; }; }

month_weekday_last represents the last weekday of a month, of an as yet unspecified year.

To do this the month_weekday_last stores a month and a weekday_last.

[Example 1: constexpr auto mwd = February/Tuesday[last]; // mwd is the last Tuesday of February of an as yet unspecified year static_assert(mwd.month() == February); static_assert(mwd.weekday_last() == Tuesday[last]); — end example]

month_weekday_last is a trivially copyable and standard-layout class type.

30.8.12.2 Member functions [time.cal.mwdlast.members]

🔗

constexpr month_weekday_last(const chrono::month& m,
                             const chrono::weekday_last& wdl) noexcept;

Effects: Initializes m_ with m, and wdl_ with wdl.

🔗

constexpr chrono::month month() const noexcept;

Returns: m_.

🔗

constexpr chrono::weekday_last weekday_last() const noexcept;

Returns: wdl_.

🔗

constexpr bool ok() const noexcept;

Returns: m_.ok() && wdl_.ok().

30.8.12.3 Non-member functions [time.cal.mwdlast.nonmembers]

🔗

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

Returns: x.month() == y.month() && x.weekday_last() == y.weekday_last().

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L}/{:L}"), mwdl.month(), mwdl.weekday_last());

30.8.13 Class year_month [time.cal.ym]

30.8.13.1 Overview [time.cal.ym.overview]

namespace std::chrono { class year_month { chrono::year y_; // exposition only chrono::month m_; // exposition only public: year_month() = default; constexpr year_month(const chrono::year& y, const chrono::month& m) noexcept; constexpr chrono::year year() const noexcept; constexpr chrono::month month() const noexcept; constexpr year_month& operator+=(const months& dm) noexcept; constexpr year_month& operator-=(const months& dm) noexcept; constexpr year_month& operator+=(const years& dy) noexcept; constexpr year_month& operator-=(const years& dy) noexcept; constexpr bool ok() const noexcept; }; }

year_month represents a specific month of a specific year, but with an unspecified day.

year_month is a field-based time point with a resolution of months.

year_month meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements.

year_month is a trivially copyable and standard-layout class type.

30.8.13.2 Member functions [time.cal.ym.members]

🔗

constexpr year_month(const chrono::year& y, const chrono::month& m) noexcept;

Effects: Initializes y_ with y, and m_ with m.

🔗

constexpr chrono::year year() const noexcept;

Returns: y_.

🔗

constexpr chrono::month month() const noexcept;

Returns: m_.

🔗

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

Constraints: If the argument supplied by the caller for the months parameter is convertible to years, its implicit conversion sequence to years is worse than its implicit conversion sequence to months ([over.ics.rank]).

Effects: *this = *this + dm.

Returns: *this.

🔗

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

Effects: *this = *this - dm.

Returns: *this.

🔗

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

Effects: *this = *this + dy.

Returns: *this.

🔗

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

Effects: *this = *this - dy.

Returns: *this.

🔗

constexpr bool ok() const noexcept;

Returns: y_.ok() && m_.ok().

30.8.13.3 Non-member functions [time.cal.ym.nonmembers]

🔗

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

Returns: x.year() == y.year() && x.month() == y.month().

🔗

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

Effects: Equivalent to: if (auto c = x.year() <=> y.year(); c != 0) return c; return x.month() <=> y.month();

🔗

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

Returns: A year_month value z such that z.ok() && z - ym == dm is true.

Complexity:

O (1)

with respect to the value of dm.

🔗

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

Returns: ym + dm.

🔗

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

Returns: ym + -dm.

🔗

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

Returns: x.year() - y.year() + months{static_cast<int>(unsigned{x.month()}) - static_cast<int>(unsigned{y.month()})}

🔗

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

Returns: (ym.year() + dy) / ym.month().

🔗

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

Returns: ym + dy.

🔗

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

Returns: ym + -dy.

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{}/{:L}"), ym.year(), ym.month());

🔗

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);

Effects: Attempts to parse the input stream is into the year_month ym using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid year_month, is.setstate(ios_base::failbit) is called and ym is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

30.8.14 Class year_month_day [time.cal.ymd]

30.8.14.1 Overview [time.cal.ymd.overview]

namespace std::chrono { class year_month_day { chrono::year y_; // exposition only chrono::month m_; // exposition only chrono::day d_; // exposition only public: year_month_day() = default; constexpr year_month_day(const chrono::year& y, const chrono::month& m, const chrono::day& d) noexcept; constexpr year_month_day(const year_month_day_last& ymdl) noexcept; constexpr year_month_day(const sys_days& dp) noexcept; constexpr explicit year_month_day(const local_days& dp) noexcept; constexpr year_month_day& operator+=(const months& m) noexcept; constexpr year_month_day& operator-=(const months& m) noexcept; constexpr year_month_day& operator+=(const years& y) noexcept; constexpr year_month_day& operator-=(const years& y) noexcept; constexpr chrono::year year() const noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::day day() const noexcept; constexpr operator sys_days() const noexcept; constexpr explicit operator local_days() const noexcept; constexpr bool ok() const noexcept; }; }

year_month_day represents a specific year, month, and day.

year_month_day is a field-based time point with a resolution of days.

[Note 1:

year_month_day supports years- and months-oriented arithmetic, but not days-oriented arithmetic.

For the latter, there is a conversion to sys_days, which efficiently supports days-oriented arithmetic.

— end note]

year_month_day meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements.

year_month_day is a trivially copyable and standard-layout class type.

30.8.14.2 Member functions [time.cal.ymd.members]

🔗

constexpr year_month_day(const chrono::year& y, const chrono::month& m,
                         const chrono::day& d) noexcept;

Effects: Initializes y_ with y, m_ with m, and d_ with d.

🔗

constexpr year_month_day(const year_month_day_last& ymdl) noexcept;

Effects: Initializes y_ with ymdl.year(), m_ with ymdl.month(), and d_ with ymdl.day().

[Note 1:

This conversion from year_month_day_last to year_month_day can be more efficient than converting a year_month_day_last to a sys_days, and then converting that sys_days to a year_month_day.

— end note]

🔗

constexpr year_month_day(const sys_days& dp) noexcept;

Effects: Constructs an object of type year_month_day that corresponds to the date represented by dp.

Remarks: For any value ymd of type year_month_day for which ymd.ok() is true, ymd == year_month_day{sys_days{ymd}} is true.

🔗

constexpr explicit year_month_day(const local_days& dp) noexcept;

Effects: Equivalent to constructing with sys_days{dp.time_since_epoch()}.

🔗

constexpr year_month_day& operator+=(const months& m) noexcept;

Effects: *this = *this + m.

Returns: *this.

🔗

constexpr year_month_day& operator-=(const months& m) noexcept;

Effects: *this = *this - m.

Returns: *this.

🔗

constexpr year_month_day& year_month_day::operator+=(const years& y) noexcept;

Effects: *this = *this + y.

Returns: *this.

🔗

constexpr year_month_day& year_month_day::operator-=(const years& y) noexcept;

Effects: *this = *this - y.

Returns: *this.

🔗

constexpr chrono::year year() const noexcept;

Returns: y_.

🔗

constexpr chrono::month month() const noexcept;

Returns: m_.

🔗

constexpr chrono::day day() const noexcept;

Returns: d_.

🔗

constexpr operator sys_days() const noexcept;

Returns: If ok(), returns a sys_days holding a count of days from the sys_days epoch to *this (a negative value if *this represents a date prior to the sys_days epoch).

Otherwise, if y_.ok() && m_.ok() is true, returns sys_days{y_/m_/1d} + (d_ - 1d).

Otherwise the value returned is unspecified.

Remarks: A sys_days in the range [days{-12687428}, days{11248737}] which is converted to a year_month_day has the same value when converted back to a sys_days.

[Example 1: static_assert(year_month_day{sys_days{2017y/January/0}} == 2016y/December/31); static_assert(year_month_day{sys_days{2017y/January/31}} == 2017y/January/31); static_assert(year_month_day{sys_days{2017y/January/32}} == 2017y/February/1); — end example]

🔗

constexpr explicit operator local_days() const noexcept;

Returns: local_days{sys_days{*this}.time_since_epoch()}.

🔗

constexpr bool ok() const noexcept;

Returns: If y_.ok() is true, and m_.ok() is true, and d_ is in the range [1d, (y_/m_/last).day()], then returns true; otherwise returns false.

30.8.14.3 Non-member functions [time.cal.ymd.nonmembers]

🔗

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

Returns: x.year() == y.year() && x.month() == y.month() && x.day() == y.day().

🔗

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

Effects: Equivalent to: if (auto c = x.year() <=> y.year(); c != 0) return c; if (auto c = x.month() <=> y.month(); c != 0) return c; return x.day() <=> y.day();

🔗

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

Returns: (ymd.year() / ymd.month() + dm) / ymd.day().

[Note 1:

If ymd.day() is in the range [1d, 28d], ok() will return true for the resultant year_month_day.

— end note]

🔗

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

Returns: ymd + dm.

🔗

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

Returns: ymd + (-dm).

🔗

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

Returns: (ymd.year() + dy) / ymd.month() / ymd.day().

[Note 2:

If ymd.month() is February and ymd.day() is not in the range [1d, 28d], ok() can return false for the resultant year_month_day.

— end note]

🔗

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

Returns: ymd + dy.

🔗

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

Returns: ymd + (-dy).

🔗

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

Effects: Equivalent to: return os << (ymd.ok() ? format(STATICALLY-WIDEN<charT>("{:%F}"), ymd) : format(STATICALLY-WIDEN<charT>("{:%F} is not a valid date"), 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);

Effects: Attempts to parse the input stream is into the year_month_day ymd using the format flags given in the NTCTS fmt as specified in [time.parse].

If the parse fails to decode a valid year_month_day, is.setstate(ios_base::failbit) is called and ymd is not modified.

If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.

If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.

Returns: is.

30.8.15 Class year_month_day_last [time.cal.ymdlast]

30.8.15.1 Overview [time.cal.ymdlast.overview]

namespace std::chrono { class year_month_day_last { chrono::year y_; // exposition only chrono::month_day_last mdl_; // exposition only public: constexpr year_month_day_last(const chrono::year& y, const chrono::month_day_last& mdl) noexcept; constexpr year_month_day_last& operator+=(const months& m) noexcept; constexpr year_month_day_last& operator-=(const months& m) noexcept; constexpr year_month_day_last& operator+=(const years& y) noexcept; constexpr year_month_day_last& operator-=(const years& y) noexcept; constexpr chrono::year year() const noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::month_day_last month_day_last() const noexcept; constexpr chrono::day day() const noexcept; constexpr operator sys_days() const noexcept; constexpr explicit operator local_days() const noexcept; constexpr bool ok() const noexcept; }; }

year_month_day_last represents the last day of a specific year and month.

year_month_day_last is a field-based time point with a resolution of days, except that it is restricted to pointing to the last day of a year and month.

[Note 1:

year_month_day_last supports years- and months-oriented arithmetic, but not days-oriented arithmetic.

For the latter, there is a conversion to sys_days, which efficiently supports days-oriented arithmetic.

— end note]

year_month_day_last meets the Cpp17EqualityComparable (Table 28) and Cpp17LessThanComparable (Table 29) requirements.

year_month_day_last is a trivially copyable and standard-layout class type.

30.8.15.2 Member functions [time.cal.ymdlast.members]

🔗

constexpr year_month_day_last(const chrono::year& y,
                              const chrono::month_day_last& mdl) noexcept;

Effects: Initializes y_ with y and mdl_ with mdl.

🔗

constexpr year_month_day_last& operator+=(const months& m) noexcept;

Effects: *this = *this + m.

Returns: *this.

🔗

constexpr year_month_day_last& operator-=(const months& m) noexcept;

Effects: *this = *this - m.

Returns: *this.

🔗

constexpr year_month_day_last& operator+=(const years& y) noexcept;

Effects: *this = *this + y.

Returns: *this.

🔗

constexpr year_month_day_last& operator-=(const years& y) noexcept;

Effects: *this = *this - y.

Returns: *this.

🔗

constexpr chrono::year year() const noexcept;

Returns: y_.

🔗

constexpr chrono::month month() const noexcept;

Returns: mdl_.month().

🔗

constexpr chrono::month_day_last month_day_last() const noexcept;

Returns: mdl_.

🔗

constexpr chrono::day day() const noexcept;

Returns: If ok() is true, returns a day representing the last day of the (year, month) pair represented by *this.

Otherwise, the returned value is unspecified.

[Note 1:

This value might be computed on demand.

— end note]

🔗

constexpr operator sys_days() const noexcept;

Returns: sys_days{year()/month()/day()}.

🔗

constexpr explicit operator local_days() const noexcept;

Returns: local_days{sys_days{*this}.time_since_epoch()}.

🔗

constexpr bool ok() const noexcept;

Returns: y_.ok() && mdl_.ok().

30.8.15.3 Non-member functions [time.cal.ymdlast.nonmembers]

🔗

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

Returns: x.year() == y.year() && x.month_day_last() == y.month_day_last().

🔗

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

Effects: Equivalent to: if (auto c = x.year() <=> y.year(); c != 0) return c; return x.month_day_last() <=> y.month_day_last();

🔗

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

Returns: (ymdl.year() / ymdl.month() + dm) / last.

🔗

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

Returns: ymdl + dm.

🔗

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

Returns: ymdl + (-dm).

🔗

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

Returns: {ymdl.year()+dy, ymdl.month_day_last()}.

🔗

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

Returns: ymdl + dy.

🔗

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

Returns: ymdl + (-dy).

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{}/{:L}"), ymdl.year(), ymdl.month_day_last());

30.8.16 Class year_month_weekday [time.cal.ymwd]

30.8.16.1 Overview [time.cal.ymwd.overview]

namespace std::chrono { class year_month_weekday { chrono::year y_; // exposition only chrono::month m_; // exposition only chrono::weekday_indexed wdi_; // exposition only public: year_month_weekday() = default; constexpr year_month_weekday(const chrono::year& y, const chrono::month& m, const chrono::weekday_indexed& wdi) noexcept; constexpr year_month_weekday(const sys_days& dp) noexcept; constexpr explicit year_month_weekday(const local_days& dp) noexcept; constexpr year_month_weekday& operator+=(const months& m) noexcept; constexpr year_month_weekday& operator-=(const months& m) noexcept; constexpr year_month_weekday& operator+=(const years& y) noexcept; constexpr year_month_weekday& operator-=(const years& y) noexcept; constexpr chrono::year year() const noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::weekday weekday() const noexcept; constexpr unsigned index() const noexcept; constexpr chrono::weekday_indexed weekday_indexed() const noexcept; constexpr operator sys_days() const noexcept; constexpr explicit operator local_days() const noexcept; constexpr bool ok() const noexcept; }; }

year_month_weekday represents a specific year, month, and

n^{th}

weekday of the month.

year_month_weekday is a field-based time point with a resolution of days.

[Note 1:

year_month_weekday supports years- and months-oriented arithmetic, but not days-oriented arithmetic.

For the latter, there is a conversion to sys_days, which efficiently supports days-oriented arithmetic.

— end note]

year_month_weekday meets the Cpp17EqualityComparable (Table 28) requirements.

year_month_weekday is a trivially copyable and standard-layout class type.

30.8.16.2 Member functions [time.cal.ymwd.members]

🔗

constexpr year_month_weekday(const chrono::year& y, const chrono::month& m,
                             const chrono::weekday_indexed& wdi) noexcept;

Effects: Initializes y_ with y, m_ with m, and wdi_ with wdi.

🔗

constexpr year_month_weekday(const sys_days& dp) noexcept;

Effects: Constructs an object of type year_month_weekday which corresponds to the date represented by dp.

Remarks: For any value ymwd of type year_month_weekday for which ymwd.ok() is true, ymwd == year_month_weekday{sys_days{ymwd}} is true.

🔗

constexpr explicit year_month_weekday(const local_days& dp) noexcept;

Effects: Equivalent to constructing with sys_days{dp.time_since_epoch()}.

🔗

constexpr year_month_weekday& operator+=(const months& m) noexcept;

Effects: *this = *this + m.

Returns: *this.

🔗

constexpr year_month_weekday& operator-=(const months& m) noexcept;

Effects: *this = *this - m.

Returns: *this.

🔗

constexpr year_month_weekday& operator+=(const years& y) noexcept;

Effects: *this = *this + y.

Returns: *this.

🔗

constexpr year_month_weekday& operator-=(const years& y) noexcept;

Effects: *this = *this - y.

Returns: *this.

🔗

constexpr chrono::year year() const noexcept;

Returns: y_.

🔗

constexpr chrono::month month() const noexcept;

Returns: m_.

🔗

constexpr chrono::weekday weekday() const noexcept;

Returns: wdi_.weekday().

🔗

constexpr unsigned index() const noexcept;

Returns: wdi_.index().

🔗

constexpr chrono::weekday_indexed weekday_indexed() const noexcept;

Returns: wdi_.

🔗

constexpr operator sys_days() const noexcept;

Returns: If y_.ok() && m_.ok() && wdi_.weekday().ok(), returns a sys_days that represents the date (index() - 1) * 7 days after the first weekday() of year()/month().

If index() is 0 the returned sys_days represents the date 7 days prior to the first weekday() of year()/month().

Otherwise the returned value is unspecified.

🔗

constexpr explicit operator local_days() const noexcept;

Returns: local_days{sys_days{*this}.time_since_epoch()}.

🔗

constexpr bool ok() const noexcept;

Returns: If any of y_.ok(), m_.ok(), or wdi_.ok() is false, returns false.

Otherwise, if *this represents a valid date, returns true.

Otherwise, returns false.

30.8.16.3 Non-member functions [time.cal.ymwd.nonmembers]

🔗

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

Returns: x.year() == y.year() && x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed()

🔗

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

Returns: (ymwd.year() / ymwd.month() + dm) / ymwd.weekday_indexed().

🔗

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

Returns: ymwd + dm.

🔗

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

Returns: ymwd + (-dm).

🔗

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

Returns: {ymwd.year()+dy, ymwd.month(), ymwd.weekday_indexed()}.

🔗

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

Returns: ymwd + dy.

🔗

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

Returns: ymwd + (-dy).

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{}/{:L}/{:L}"), ymwd.year(), ymwd.month(), ymwd.weekday_indexed());

30.8.17 Class year_month_weekday_last [time.cal.ymwdlast]

30.8.17.1 Overview [time.cal.ymwdlast.overview]

namespace std::chrono { class year_month_weekday_last { chrono::year y_; // exposition only chrono::month m_; // exposition only chrono::weekday_last wdl_; // exposition only public: constexpr year_month_weekday_last(const chrono::year& y, const chrono::month& m, const chrono::weekday_last& wdl) noexcept; constexpr year_month_weekday_last& operator+=(const months& m) noexcept; constexpr year_month_weekday_last& operator-=(const months& m) noexcept; constexpr year_month_weekday_last& operator+=(const years& y) noexcept; constexpr year_month_weekday_last& operator-=(const years& y) noexcept; constexpr chrono::year year() const noexcept; constexpr chrono::month month() const noexcept; constexpr chrono::weekday weekday() const noexcept; constexpr chrono::weekday_last weekday_last() const noexcept; constexpr operator sys_days() const noexcept; constexpr explicit operator local_days() const noexcept; constexpr bool ok() const noexcept; }; }

year_month_weekday_last represents a specific year, month, and last weekday of the month.

year_month_weekday_last is a field-based time point with a resolution of days, except that it is restricted to pointing to the last weekday of a year and month.

[Note 1:

year_month_weekday_last supports years- and months-oriented arithmetic, but not days-oriented arithmetic.

For the latter, there is a conversion to sys_days, which efficiently supports days-oriented arithmetic.

— end note]

year_month_weekday_last meets the Cpp17EqualityComparable (Table 28) requirements.

year_month_weekday_last is a trivially copyable and standard-layout class type.

30.8.17.2 Member functions [time.cal.ymwdlast.members]

🔗

constexpr year_month_weekday_last(const chrono::year& y, const chrono::month& m,
                                  const chrono::weekday_last& wdl) noexcept;

Effects: Initializes y_ with y, m_ with m, and wdl_ with wdl.

🔗

constexpr year_month_weekday_last& operator+=(const months& m) noexcept;

Effects: *this = *this + m.

Returns: *this.

🔗

constexpr year_month_weekday_last& operator-=(const months& m) noexcept;

Effects: *this = *this - m.

Returns: *this.

🔗

constexpr year_month_weekday_last& operator+=(const years& y) noexcept;

Effects: *this = *this + y.

Returns: *this.

🔗

constexpr year_month_weekday_last& operator-=(const years& y) noexcept;

Effects: *this = *this - y.

Returns: *this.

🔗

constexpr chrono::year year() const noexcept;

Returns: y_.

🔗

constexpr chrono::month month() const noexcept;

Returns: m_.

🔗

constexpr chrono::weekday weekday() const noexcept;

Returns: wdl_.weekday().

🔗

constexpr chrono::weekday_last weekday_last() const noexcept;

Returns: wdl_.

🔗

constexpr operator sys_days() const noexcept;

Returns: If ok() == true, returns a sys_days that represents the last weekday() of year()/month().

Otherwise the returned value is unspecified.

🔗

constexpr explicit operator local_days() const noexcept;

Returns: local_days{sys_days{*this}.time_since_epoch()}.

🔗

constexpr bool ok() const noexcept;

Returns: y_.ok() && m_.ok() && wdl_.ok().

30.8.17.3 Non-member functions [time.cal.ymwdlast.nonmembers]

🔗

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

Returns: x.year() == y.year() && x.month() == y.month() && x.weekday_last() == y.weekday_last()

🔗

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

Returns: (ymwdl.year() / ymwdl.month() + dm) / ymwdl.weekday_last().

🔗

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

Returns: ymwdl + dm.

🔗

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

Returns: ymwdl + (-dm).

🔗

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

Returns: {ymwdl.year()+dy, ymwdl.month(), ymwdl.weekday_last()}.

🔗

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

Returns: ymwdl + dy.

🔗

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

Returns: ymwdl + (-dy).

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{}/{:L}/{:L}"), ymwdl.year(), ymwdl.month(), ymwdl.weekday_last());

30.8.18 Conventional syntax operators [time.cal.operators]

A set of overloaded operator/ functions provides a conventional syntax for the creation of civil calendar dates.

[Note 1:

The year, month, and day are accepted in any of the following 3 orders: year/month/day month/day/year day/month/year

Anywhere a day is needed, any of the following can also be specified: last weekday[i] weekday[last]

— end note]

[Note 2:

Partial-date types such as year_month and month_day can be created by not applying the second division operator for any of the three orders.

For example: year_month ym = 2015y/April; month_day md1 = April/4; month_day md2 = 4d/April;

— end note]

[Example 1: auto a = 2015/4/4; // a == int(125) auto b = 2015y/4/4; // b == year_month_day{year(2015), month(4), day(4)} auto c = 2015y/4d/April; // error: no viable operator/ for first / auto d = 2015/April/4; // error: no viable operator/ for first / — end example]

🔗

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

Returns: {y, m}.

🔗

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

Returns: y / month(m).

🔗

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

Returns: {m, d}.

🔗

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

Returns: m / day(d).

🔗

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

Returns: month(m) / d.

🔗

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

Returns: m / d.

🔗

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

Returns: month(m) / d.

🔗

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

Returns: month_day_last{m}.

🔗

constexpr month_day_last
  operator/(int m, last_spec) noexcept;

Returns: month(m) / last.

🔗

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

Returns: m / last.

🔗

constexpr month_day_last
  operator/(last_spec, int m) noexcept;

Returns: month(m) / last.

🔗

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

Returns: {m, wdi}.

🔗

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

Returns: month(m) / wdi.

🔗

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

Returns: m / wdi.

🔗

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

Returns: month(m) / wdi.

🔗

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

Returns: {m, wdl}.

🔗

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

Returns: month(m) / wdl.

🔗

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

Returns: m / wdl.

🔗

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

Returns: month(m) / wdl.

🔗

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

Returns: {ym.year(), ym.month(), d}.

🔗

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

Returns: ym / day(d).

🔗

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

Returns: y / md.month() / md.day().

🔗

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

Returns: year(y) / md.

🔗

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

Returns: y / md.

🔗

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

Returns: year(y) / md.

🔗

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

Returns: {ym.year(), month_day_last{ym.month()}}.

🔗

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

Returns: {y, mdl}.

🔗

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

Returns: year(y) / mdl.

🔗

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

Returns: y / mdl.

🔗

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

Returns: year(y) / mdl.

🔗

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

Returns: {ym.year(), ym.month(), wdi}.

🔗

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

Returns: {y, mwd.month(), mwd.weekday_indexed()}.

🔗

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

Returns: year(y) / mwd.

🔗

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

Returns: y / mwd.

🔗

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

Returns: year(y) / mwd.

🔗

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

Returns: {ym.year(), ym.month(), wdl}.

🔗

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

Returns: {y, mwdl.month(), mwdl.weekday_last()}.

🔗

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

Returns: year(y) / mwdl.

🔗

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

Returns: y / mwdl.

🔗

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

Returns: year(y) / mwdl.

30.9 Class template hh_mm_ss [time.hms]

30.9.1 Overview [time.hms.overview]

namespace std::chrono { template<class Duration> class hh_mm_ss { public: static constexpr unsigned fractional_width = see below; using precision = see below; constexpr hh_mm_ss() noexcept : hh_mm_ss{Duration::zero()} {} constexpr explicit hh_mm_ss(Duration d); constexpr bool is_negative() const noexcept; constexpr chrono::hours hours() const noexcept; constexpr chrono::minutes minutes() const noexcept; constexpr chrono::seconds seconds() const noexcept; constexpr precision subseconds() const noexcept; constexpr explicit operator precision() const noexcept; constexpr precision to_duration() const noexcept; private: bool is_neg; // exposition only chrono::hours h; // exposition only chrono::minutes m; // exposition only chrono::seconds s; // exposition only precision ss; // exposition only }; }

The hh_mm_ss class template splits a duration into a multi-field time structure hours:minutes:seconds and possibly subseconds, where subseconds will be a duration unit based on a non-positive power of 10.

The Duration template parameter dictates the precision to which the time is split.

A hh_mm_ss models negative durations with a distinct is_negative getter that returns true when the input duration is negative.

The individual duration fields always return non-negative durations even when is_negative() indicates the structure is representing a negative duration.

If Duration is not a specialization of duration, the program is ill-formed.

30.9.2 Members [time.hms.members]

🔗

static constexpr unsigned fractional_width = see below;

fractional_width is the number of fractional decimal digits represented by precision.

fractional_width has the value of the smallest possible integer in the range [0, 18] such that precision will exactly represent all values of Duration.

If no such value of fractional_width exists, then fractional_width is 6.

[Example 1:

See Table 127 for some durations, the resulting fractional_width, and the formatted fractional second output of Duration{1}.

Table 127 — Examples for fractional_width [tab:time.hms.width]

🔗 Duration	fractional_width	Formatted fractional second output
🔗 hours, minutes, and seconds	0
🔗 milliseconds	3	0.001
🔗 microseconds	6	0.000001
🔗 nanoseconds	9	0.000000001
🔗 duration<int, ratio<1, 2>>	1	0.5
🔗 duration<int, ratio<1, 3>>	6	0.333333
🔗 duration<int, ratio<1, 4>>	2	0.25
🔗 duration<int, ratio<1, 5>>	1	0.2
🔗 duration<int, ratio<1, 6>>	6	0.166666
🔗 duration<int, ratio<1, 7>>	6	0.142857
🔗 duration<int, ratio<1, 8>>	3	0.125
🔗 duration<int, ratio<1, 9>>	6	0.111111
🔗 duration<int, ratio<1, 10>>	1	0.1
🔗 duration<int, ratio<756, 625>>	4	0.2096

— end example]

🔗

using precision = see below;

precision is duration<common_type_t<Duration::rep, seconds::rep>, ratio<1,

10fractional_width

🔗

constexpr explicit hh_mm_ss(Duration d);

Effects: Constructs an object of type hh_mm_ss which represents the Duration d with precision precision.

(3.1)
Initializes is_neg with d < Duration::zero().
(3.2)
Initializes h with duration_cast<chrono::hours>(abs(d)).
(3.3)
Initializes m with duration_cast<chrono::minutes>(abs(d) - hours()).
(3.4)
Initializes s with duration_cast<chrono::seconds>(abs(d) - hours() - minutes()).
(3.5)
If treat_as_floating_point_v<precision::rep> is true, initializes ss with abs(d) - hours() - minutes() - seconds().

Otherwise, initializes ss with duration_cast<precision>(abs(d) - hours() - minutes() - seconds()).

[Note 1:

When precision::rep is integral and precision::period is ratio<1>, subseconds() always returns a value equal to 0s.

— end note]

Postconditions: If treat_as_floating_point_v<precision::rep> is true, to_duration() returns d, otherwise to_duration() returns duration_cast<precision>(d).

🔗

constexpr bool is_negative() const noexcept;

Returns: is_neg.

🔗

constexpr chrono::hours hours() const noexcept;

Returns: h.

🔗

constexpr chrono::minutes minutes() const noexcept;

Returns: m.

🔗

constexpr chrono::seconds seconds() const noexcept;

Returns: s.

🔗

constexpr precision subseconds() const noexcept;

Returns: ss.

🔗

constexpr precision to_duration() const noexcept;

Returns: If is_neg, returns -(h + m + s + ss), otherwise returns h + m + s + ss.

🔗

constexpr explicit operator precision() const noexcept;

Returns: to_duration().

30.9.3 Non-members [time.hms.nonmembers]

🔗

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

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%T}"), hms);

[Example 1: for (auto ms : {-4083007ms, 4083007ms, 65745123ms}) { hh_mm_ss hms{ms}; cout << hms << '\n'; } cout << hh_mm_ss{65745s} << '\n';

Produces the output (assuming the "C" locale): -01:08:03.007 01:08:03.007 18:15:45.123 18:15:45

— end example]

30.10 12/24 hours functions [time.12]

These functions aid in translating between a 12h format time of day and a 24h format time of day.

🔗

constexpr bool is_am(const hours& h) noexcept;

Returns: 0h <= h && h <= 11h.

🔗

constexpr bool is_pm(const hours& h) noexcept;

Returns: 12h <= h && h <= 23h.

🔗

constexpr hours make12(const hours& h) noexcept;

Returns: The 12-hour equivalent of h in the range [1h, 12h].

If h is not in the range [0h, 23h], the value returned is unspecified.

🔗

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

Returns: If is_pm is false, returns the 24-hour equivalent of h in the range [0h, 11h], assuming h represents an ante meridiem hour.

Otherwise, returns the 24-hour equivalent of h in the range [12h, 23h], assuming h represents a post meridiem hour.

If h is not in the range [1h, 12h], the value returned is unspecified.

30.11 Time zones [time.zone]

30.11.1 General [time.zone.general]

[time.zone] describes an interface for accessing the IANA Time Zone Database[bib] that interoperates with sys_time and local_time.

This interface provides time zone support to both the civil calendar types ([time.cal]) and to user-defined calendars.

30.11.2 Time zone database [time.zone.db]

30.11.2.1 Class tzdb [time.zone.db.tzdb]

namespace std::chrono { struct tzdb { string version; vector<time_zone> zones; vector<time_zone_link> links; vector<leap_second> leap_seconds; const time_zone* locate_zone(string_view tz_name) const; const time_zone* current_zone() const; }; }

Each vector in a tzdb object is sorted to enable fast lookup.

🔗

const time_zone* locate_zone(string_view tz_name) const;

Returns:

(2.1)
If zones contains an element tz for which tz.name() == tz_name, a pointer to tz;
(2.2)
otherwise, if links contains an element tz_l for which tz_l.name() == tz_name, then a pointer to the element tz of zones for which tz.name() == tz_l.target().

[Note 1:

A time_zone_link specifies an alternative name for a time_zone.

— end note]

Throws: If a const time_zone* cannot be found as described in the Returns: element, throws a runtime_error.

[Note 2:

On non-exceptional return, the return value is always a pointer to a valid time_zone.

— end note]

🔗

const time_zone* current_zone() const;

Returns: A pointer to the time zone which the computer has set as its local time zone.

30.11.2.2 Class tzdb_list [time.zone.db.list]

namespace std::chrono { class tzdb_list { public: tzdb_list(const tzdb_list&) = delete; tzdb_list& operator=(const tzdb_list&) = delete; // unspecified additional constructors class const_iterator; const tzdb& front() const noexcept; const_iterator erase_after(const_iterator p); const_iterator begin() const noexcept; const_iterator end() const noexcept; const_iterator cbegin() const noexcept; const_iterator cend() const noexcept; }; }

The tzdb_list database is a singleton; the unique object of type tzdb_list can be accessed via the get_tzdb_list() function.

[Note 1:

This access is only needed for those applications that need to have long uptimes and have a need to update the time zone database while running.

Other applications can implicitly access the front() of this list via the read-only namespace scope functions get_tzdb(), locate_zone(), and current_zone().

— end note]

The tzdb_list object contains a list of tzdb objects.

tzdb_list::const_iterator is a constant iterator which meets the Cpp17ForwardIterator requirements and has a value type of tzdb.

🔗

const tzdb& front() const noexcept;

Synchronization: This operation is thread-safe with respect to reload_tzdb().

[Note 2:

reload_tzdb() pushes a new tzdb onto the front of this container.

— end note]

Returns: A reference to the first tzdb in the container.

🔗

const_iterator erase_after(const_iterator p);

Preconditions: The iterator following p is dereferenceable.

Effects: Erases the tzdb referred to by the iterator following p.

Postconditions: No pointers, references, or iterators are invalidated except those referring to the erased tzdb.

[Note 3:

It is not possible to erase the tzdb referred to by begin().

— end note]

Returns: An iterator pointing to the element following the one that was erased, or end() if no such element exists.

Throws: Nothing.

🔗

const_iterator begin() const noexcept;

Returns: An iterator referring to the first tzdb in the container.

🔗

const_iterator end() const noexcept;

Returns: An iterator referring to the position one past the last tzdb in the container.

🔗

const_iterator cbegin() const noexcept;

Returns: begin().

🔗

const_iterator cend() const noexcept;

Returns: end().

30.11.2.3 Time zone database access [time.zone.db.access]

🔗

tzdb_list& get_tzdb_list();

Effects: If this is the first access to the time zone database, initializes the database.

If this call initializes the database, the resulting database will be a tzdb_list holding a single initialized tzdb.

Synchronization: It is safe to call this function from multiple threads at one time.

Returns: A reference to the database.

Throws: runtime_error if for any reason a reference cannot be returned to a valid tzdb_list containing one or more valid tzdbs.

🔗

const tzdb& get_tzdb();

Returns: get_tzdb_list().front().

🔗

const time_zone* locate_zone(string_view tz_name);

Returns: get_tzdb().locate_zone(tz_name).

[Note 1:

The time zone database will be initialized if this is the first reference to the database.

— end note]

🔗

const time_zone* current_zone();

Returns: get_tzdb().current_zone().

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

The local time zone database is that supplied by the implementation when the program first accesses the database, for example via current_zone().

While the program is running, the implementation may choose to update the time zone database.

This update shall not impact the program in any way unless the program calls the functions in this subclause.

This potentially updated time zone database is referred to as the remote time zone database.

🔗

const tzdb& reload_tzdb();

Effects: This function first checks the version of the remote time zone database.

If the versions of the local and remote databases are the same, there are no effects.

Otherwise the remote database is pushed to the front of the tzdb_list accessed by get_tzdb_list().

Synchronization: This function is thread-safe with respect to get_tzdb_list().front() and get_tzdb_list().erase_after().

Postconditions: No pointers, references, or iterators are invalidated.

Returns: get_tzdb_list().front().

Throws: runtime_error if for any reason a reference cannot be returned to a valid tzdb.

🔗

string remote_version();

Returns: The latest remote database version.

[Note 1:

This can be compared with get_tzdb().version to discover if the local and remote databases are equivalent.

— end note]

30.11.3 Exception classes [time.zone.exception]

30.11.3.1 Class nonexistent_local_time [time.zone.exception.nonexist]

namespace std::chrono { class nonexistent_local_time : public runtime_error { public: template<class Duration> nonexistent_local_time(const local_time<Duration>& tp, const local_info& i); }; }

nonexistent_local_time is thrown when an attempt is made to convert a non-existent local_time to a sys_time without specifying choose::earliest or choose::latest.

🔗

template<class Duration>
  nonexistent_local_time(const local_time<Duration>& tp, const local_info& i);

Preconditions: i.result == local_info::nonexistent is true.

Effects: Initializes the base class with a sequence of char equivalent to that produced by os.str() initialized as shown below: ostringstream os; os << tp << " is in a gap between\n" << local_seconds{i.first.end.time_since_epoch()} + i.first.offset << ' ' << i.first.abbrev << " and\n" << local_seconds{i.second.begin.time_since_epoch()} + i.second.offset << ' ' << i.second.abbrev << " which are both equivalent to\n" << i.first.end << " UTC";

[Example 1: #include <chrono> #include <iostream> int main() { using namespace std::chrono; try { auto zt = zoned_time{"America/New_York", local_days{Sunday[2]/March/2016} + 2h + 30min}; } catch (const nonexistent_local_time& e) { std::cout << e.what() << '\n'; } }

Produces the output:

2016-03-13 02:30:00 is in a gap between
2016-03-13 02:00:00 EST and
2016-03-13 03:00:00 EDT which are both equivalent to
2016-03-13 07:00:00 UTC

— end example]

30.11.3.2 Class ambiguous_local_time [time.zone.exception.ambig]

namespace std::chrono { class ambiguous_local_time : public runtime_error { public: template<class Duration> ambiguous_local_time(const local_time<Duration>& tp, const local_info& i); }; }

ambiguous_local_time is thrown when an attempt is made to convert an ambiguous local_time to a sys_time without specifying choose::earliest or choose::latest.

🔗

template<class Duration>
  ambiguous_local_time(const local_time<Duration>& tp, const local_info& i);

Preconditions: i.result == local_info::ambiguous is true.

Effects: Initializes the base class with a sequence of char equivalent to that produced by os.str() initialized as shown below: ostringstream os; os << tp << " is ambiguous. It could be\n" << tp << ' ' << i.first.abbrev << " == " << tp - i.first.offset << " UTC or\n" << tp << ' ' << i.second.abbrev << " == " << tp - i.second.offset << " UTC";

[Example 1: #include <chrono> #include <iostream> int main() { using namespace std::chrono; try { auto zt = zoned_time{"America/New_York", local_days{Sunday[1]/November/2016} + 1h + 30min}; } catch (const ambiguous_local_time& e) { std::cout << e.what() << '\n'; } }

Produces the output:

2016-11-06 01:30:00 is ambiguous.  It could be
2016-11-06 01:30:00 EDT == 2016-11-06 05:30:00 UTC or
2016-11-06 01:30:00 EST == 2016-11-06 06:30:00 UTC

— end example]

30.11.4 Information classes [time.zone.info]

30.11.4.1 Class sys_info [time.zone.info.sys]

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

A sys_info object can be obtained from the combination of a time_zone and either a sys_time or local_time.

It can also be obtained from a zoned_time, which is effectively a pair of a time_zone and sys_time.

[Note 1:

This type provides a low-level interface to time zone information.

Typical conversions from sys_time to local_time will use this class implicitly, not explicitly.

— end note]

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).

This information can be used to efficiently iterate the transitions of a time_zone.

The offset data member indicates the UTC offset in effect for the associated time_zone and time_point.

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

The save data member is extra information not normally needed for conversion between local_time and sys_time.

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.

However, this information should not be taken as authoritative.

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.

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).

The abbrev data member indicates the current abbreviation used for the associated time_zone and time_point.

Abbreviations are not unique among the time_zones, and so one cannot reliably map abbreviations back to a time_zone and UTC offset.

🔗

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

Effects: Streams out the sys_info object r in an unspecified format.

Returns: os.

30.11.4.2 Class local_info [time.zone.info.local]

🔗

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; }; }

[Note 1:

This type provides a low-level interface to time zone information.

Typical conversions from local_time to sys_time will use this class implicitly, not explicitly.

— end note]

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

(2.1)
When a local_time to sys_time conversion is unique, result == unique, first will be filled out with the correct sys_info, and second will be zero-initialized.
(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, and second will be filled out with the sys_info that begins just after the local_time.
(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, and second will be filled out with the sys_info that starts just before the local_time.

🔗

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

Effects: Streams out the local_info object r in an unspecified format.

Returns: os.

30.11.5 Class time_zone [time.zone.timezone]

30.11.5.1 Overview [time.zone.overview]

namespace std::chrono { class time_zone { public: time_zone(time_zone&&) = default; time_zone& operator=(time_zone&&) = default; // unspecified additional constructors string_view name() const noexcept; template<class Duration> sys_info get_info(const sys_time<Duration>& st) const; template<class Duration> local_info get_info(const local_time<Duration>& tp) const; template<class Duration> sys_time<common_type_t<Duration, seconds>> to_sys(const local_time<Duration>& tp) const; template<class Duration> sys_time<common_type_t<Duration, seconds>> to_sys(const local_time<Duration>& tp, choose z) const; template<class Duration> local_time<common_type_t<Duration, seconds>> to_local(const sys_time<Duration>& tp) const; }; }

A time_zone represents all time zone transitions for a specific geographic area.

time_zone construction is unspecified, and performed as part of database initialization.

[Note 1:

const time_zone objects can be accessed via functions such as locate_zone.

— end note]

30.11.5.2 Member functions [time.zone.members]

🔗

string_view name() const noexcept;

Returns: The name of the time_zone.

[Example 1:

"America/New_York".

— end example]

🔗

template<class Duration>
  sys_info get_info(const sys_time<Duration>& st) const;

Returns: A sys_info i for which st is in the range [i.begin, i.end).

🔗

template<class Duration>
  local_info get_info(const local_time<Duration>& tp) const;

Returns: A local_info for tp.

🔗

template<class Duration>
  sys_time<common_type_t<Duration, seconds>>
    to_sys(const local_time<Duration>& tp) const;

Returns: A sys_time that is at least as fine as seconds, and will be finer if the argument tp has finer precision.

This sys_time is the UTC equivalent of tp according to the rules of this time_zone.

Throws: If the conversion from tp to a sys_time is ambiguous, throws ambiguous_local_time.

If the tp represents a non-existent time between two UTC time_points, throws nonexistent_local_time.

🔗

template<class Duration>
  sys_time<common_type_t<Duration, seconds>>
    to_sys(const local_time<Duration>& tp, choose z) const;

Returns: A sys_time that is at least as fine as seconds, and will be finer if the argument tp has finer precision.

This sys_time is the UTC equivalent of tp according to the rules of this time_zone.

If the conversion from tp to a sys_time is ambiguous, returns the earlier sys_time if z == choose::earliest, and returns the later sys_time if z == choose::latest.

If the tp represents a non-existent time between two UTC time_points, then the two UTC time_points will be the same, and that UTC time_point will be returned.

🔗

template<class Duration>
  local_time<common_type_t<Duration, seconds>>
    to_local(const sys_time<Duration>& tp) const;

Returns: The local_time associated with tp and this time_zone.

30.11.5.3 Non-member functions [time.zone.nonmembers]

🔗

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

Returns: x.name() == y.name().

🔗

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

Returns: x.name() <=> y.name().

30.11.6 Class template zoned_traits [time.zone.zonedtraits]

namespace std::chrono { template<class T> struct zoned_traits {}; }

zoned_traits provides a means for customizing the behavior of zoned_time<Duration, TimeZonePtr> for the zoned_time default constructor, and constructors taking string_view.

A specialization for const time_zone* is provided by the implementation: namespace std::chrono { template<> struct zoned_traits<const time_zone*> { static const time_zone* default_zone(); static const time_zone* locate_zone(string_view name); }; }

🔗

static const time_zone* default_zone();

Returns: std::chrono::locate_zone("UTC").

🔗

static const time_zone* locate_zone(string_view name);

Returns: std::chrono::locate_zone(name).

30.11.7 Class template zoned_time [time.zone.zonedtime]

30.11.7.1 Overview [time.zone.zonedtime.overview]

namespace std::chrono { template<class Duration, class TimeZonePtr = const time_zone*> class zoned_time { public: using duration = common_type_t<Duration, seconds>; private: TimeZonePtr zone_; // exposition only sys_time<duration> tp_; // exposition only using traits = zoned_traits<TimeZonePtr>; // exposition only public: zoned_time(); zoned_time(const zoned_time&) = default; zoned_time& operator=(const zoned_time&) = default; zoned_time(const sys_time<Duration>& st); explicit zoned_time(TimeZonePtr z); explicit zoned_time(string_view name); template<class Duration2> zoned_time(const zoned_time<Duration2, TimeZonePtr>& y); zoned_time(TimeZonePtr z, const sys_time<Duration>& st); zoned_time(string_view name, const sys_time<Duration>& st); zoned_time(TimeZonePtr z, const local_time<Duration>& tp); zoned_time(string_view name, const local_time<Duration>& tp); zoned_time(TimeZonePtr z, const local_time<Duration>& tp, choose c); zoned_time(string_view name, const local_time<Duration>& tp, choose c); template<class Duration2, class TimeZonePtr2> zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& y); template<class Duration2, class TimeZonePtr2> zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& y, choose); template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y); template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y, choose c); zoned_time& operator=(const sys_time<Duration>& st); zoned_time& operator=(const local_time<Duration>& lt); operator sys_time<duration>() const; explicit operator local_time<duration>() const; TimeZonePtr get_time_zone() const; local_time<duration> get_local_time() const; sys_time<duration> get_sys_time() const; sys_info get_info() const; }; zoned_time() -> zoned_time<seconds>; template<class Duration> zoned_time(sys_time<Duration>) -> zoned_time<common_type_t<Duration, seconds>>; template<class TimeZonePtrOrName> using time-zone-representation = // exposition only conditional_t<is_convertible_v<TimeZonePtrOrName, string_view>, const time_zone*, remove_cvref_t<TimeZonePtrOrName>>; template<class TimeZonePtrOrName> zoned_time(TimeZonePtrOrName&&) -> zoned_time<seconds, time-zone-representation<TimeZonePtrOrName>>; template<class TimeZonePtrOrName, class Duration> zoned_time(TimeZonePtrOrName&&, sys_time<Duration>) -> zoned_time<common_type_t<Duration, seconds>, time-zone-representation<TimeZonePtrOrName>>; template<class TimeZonePtrOrName, class Duration> zoned_time(TimeZonePtrOrName&&, local_time<Duration>, choose = choose::earliest) -> zoned_time<common_type_t<Duration, seconds>, time-zone-representation<TimeZonePtrOrName>>; template<class Duration, class TimeZonePtrOrName, class TimeZonePtr2> zoned_time(TimeZonePtrOrName&&, zoned_time<Duration, TimeZonePtr2>, choose = choose::earliest) -> zoned_time<common_type_t<Duration, seconds>, time-zone-representation<TimeZonePtrOrName>>; }

zoned_time represents a logical pairing of a time_zone and a time_point with precision Duration.

zoned_time<Duration> maintains the invariant that it always refers to a valid time zone and represents a point in time that exists and is not ambiguous in that time zone.

If Duration is not a specialization of chrono::duration, the program is ill-formed.

Every constructor of zoned_time that accepts a string_view as its first parameter does not participate in class template argument deduction ([over.match.class.deduct]).

30.11.7.2 Constructors [time.zone.zonedtime.ctor]

🔗

zoned_time();

Constraints: traits::default_zone() is a well-formed expression.

Effects: Initializes zone_ with traits::default_zone() and default constructs tp_.

🔗

zoned_time(const sys_time<Duration>& st);

Constraints: traits::default_zone() is a well-formed expression.

Effects: Initializes zone_ with traits::default_zone() and tp_ with st.

🔗

explicit zoned_time(TimeZonePtr z);

Preconditions: z refers to a time zone.

Effects: Initializes zone_ with std::move(z) and default constructs tp_.

🔗

explicit zoned_time(string_view name);

Constraints: traits::locate_zone(string_view{}) is a well-formed expression and zoned_time is constructible from the return type of traits::locate_zone(string_view{}).

Effects: Initializes zone_ with traits::locate_zone(name) and default constructs tp_.

🔗

template<class Duration2>
  zoned_time(const zoned_time<Duration2, TimeZonePtr>& y);

Constraints: is_convertible_v<sys_time<Duration2>, sys_time<Duration>> is true.

Effects: Initializes zone_ with y.zone_ and tp_ with y.tp_.

🔗

zoned_time(TimeZonePtr z, const sys_time<Duration>& st);

Preconditions: z refers to a time zone.

Effects: Initializes zone_ with std::move(z) and tp_ with st.

🔗

zoned_time(string_view name, const sys_time<Duration>& st);

Constraints: zoned_time is constructible from the return type of traits::locate_zone(name) and st.

Effects: Equivalent to construction with {traits::locate_zone(name), st}.

🔗

zoned_time(TimeZonePtr z, const local_time<Duration>& tp);

Constraints: is_convertible_v< decltype(declval<TimeZonePtr&>()->to_sys(local_time<Duration>{})), sys_time<duration>> is true.

Preconditions: z refers to a time zone.

Effects: Initializes zone_ with std::move(z) and tp_ with zone_->to_sys(tp).

🔗

zoned_time(string_view name, const local_time<Duration>& tp);

Constraints: zoned_time is constructible from the return type of traits::locate_zone(name) and tp.

Effects: Equivalent to construction with {traits::locate_zone(name), tp}.

🔗

zoned_time(TimeZonePtr z, const local_time<Duration>& tp, choose c);

Constraints: is_convertible_v< decltype(declval<TimeZonePtr&>()->to_sys(local_time<Duration>{}, choose::earliest)), sys_time<duration>> is true.

Preconditions: z refers to a time zone.

Effects: Initializes zone_ with std::move(z) and tp_ with zone_->to_sys(tp, c).

🔗

zoned_time(string_view name, const local_time<Duration>& tp, choose c);

Constraints: zoned_time is constructible from the return type of traits::locate_zone(name), local_time<Duration>, and choose.

Effects: Equivalent to construction with {traits::locate_zone(name), tp, c}.

🔗

template<class Duration2, class TimeZonePtr2>
  zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& y);

Constraints: is_convertible_v<sys_time<Duration2>, sys_time<Duration>> is true.

Preconditions: z refers to a valid time zone.

Effects: Initializes zone_ with std::move(z) and tp_ with y.tp_.

🔗

template<class Duration2, class TimeZonePtr2>
  zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& y, choose);

Constraints: is_convertible_v<sys_time<Duration2>, sys_time<Duration>> is true.

Preconditions: z refers to a valid time zone.

Effects: Equivalent to construction with {z, y}.

[Note 1:

The choose parameter has no effect.

— end note]

🔗

template<class Duration2, class TimeZonePtr2>
  zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y);

Constraints: zoned_time is constructible from the return type of traits::locate_zone(name) and the type zoned_time<Duration2, TimeZonePtr2>.

Effects: Equivalent to construction with {traits::locate_zone(name), y}.

🔗

template<class Duration2, class TimeZonePtr2>
  zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y, choose c);

Constraints: zoned_time is constructible from the return type of traits::locate_zone(name), the type zoned_time<Duration2, TimeZonePtr2>, and the type choose.

Effects: Equivalent to construction with {traits::locate_zone(name), y, c}.

[Note 2:

The choose parameter has no effect.

— end note]

30.11.7.3 Member functions [time.zone.zonedtime.members]

🔗

zoned_time& operator=(const sys_time<Duration>& st);

Effects: After assignment, get_sys_time() == st.

This assignment has no effect on the return value of get_time_zone().

Returns: *this.

🔗

zoned_time& operator=(const local_time<Duration>& lt);

Effects: After assignment, get_local_time() == lt.

This assignment has no effect on the return value of get_time_zone().

Returns: *this.

🔗

operator sys_time<duration>() const;

Returns: get_sys_time().

🔗

explicit operator local_time<duration>() const;

Returns: get_local_time().

🔗

TimeZonePtr get_time_zone() const;

Returns: zone_.

🔗

local_time<duration> get_local_time() const;

Returns: zone_->to_local(tp_).

🔗

sys_time<duration> get_sys_time() const;

Returns: tp_.

🔗

sys_info get_info() const;

Returns: zone_->get_info(tp_).

30.11.7.4 Non-member functions [time.zone.zonedtime.nonmembers]

🔗

template<class Duration1, class Duration2, class TimeZonePtr>
  bool operator==(const zoned_time<Duration1, TimeZonePtr>& x,
                  const zoned_time<Duration2, TimeZonePtr>& y);

Returns: x.zone_ == y.zone_ && x.tp_ == y.tp_.

🔗

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);

Effects: Equivalent to: return os << format(os.getloc(), STATICALLY-WIDEN<charT>("{:L%F %T %Z}"), t);

30.11.8 Class leap_second [time.zone.leap]

30.11.8.1 Overview [time.zone.leap.overview]

namespace std::chrono { class leap_second { public: leap_second(const leap_second&) = default; leap_second& operator=(const leap_second&) = default; // unspecified additional constructors constexpr sys_seconds date() const noexcept; constexpr seconds value() const noexcept; }; }

Objects of type leap_second representing the date and value of the leap second insertions are constructed and stored in the time zone database when initialized.

[Example 1: for (auto& l : get_tzdb().leap_seconds) if (l <= sys_days{2018y/March/17d}) cout << l.date() << ": " << l.value() << '\n';

Produces the output:

1972-07-01 00:00:00: 1s
1973-01-01 00:00:00: 1s
1974-01-01 00:00:00: 1s
1975-01-01 00:00:00: 1s
1976-01-01 00:00:00: 1s
1977-01-01 00:00:00: 1s
1978-01-01 00:00:00: 1s
1979-01-01 00:00:00: 1s
1980-01-01 00:00:00: 1s
1981-07-01 00:00:00: 1s
1982-07-01 00:00:00: 1s
1983-07-01 00:00:00: 1s
1985-07-01 00:00:00: 1s
1988-01-01 00:00:00: 1s
1990-01-01 00:00:00: 1s
1991-01-01 00:00:00: 1s
1992-07-01 00:00:00: 1s
1993-07-01 00:00:00: 1s
1994-07-01 00:00:00: 1s
1996-01-01 00:00:00: 1s
1997-07-01 00:00:00: 1s
1999-01-01 00:00:00: 1s
2006-01-01 00:00:00: 1s
2009-01-01 00:00:00: 1s
2012-07-01 00:00:00: 1s
2015-07-01 00:00:00: 1s
2017-01-01 00:00:00: 1s

— end example]

30.11.8.2 Member functions [time.zone.leap.members]

🔗

constexpr sys_seconds date() const noexcept;

Returns: The date and time at which the leap second was inserted.

🔗

constexpr seconds value() const noexcept;

Returns: +1s to indicate a positive leap second or -1s to indicate a negative leap second.

[Note 1:

All leap seconds inserted up through 2022 were positive leap seconds.

— end note]

30.11.8.3 Non-member functions [time.zone.leap.nonmembers]

🔗

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

Returns: x.date() == y.date().

🔗

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

Returns: x.date() <=> y.date().

🔗

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

Returns: x.date() == y.

🔗

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

Returns: x.date() < y.

🔗

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

Returns: x < y.date().

🔗

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

Returns: y < x.

🔗

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

Returns: y < x.

🔗

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

Returns: !(y < x).

🔗

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

Returns: !(y < x).

🔗

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

Returns: !(x < y).

🔗

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

Returns: !(x < y).

🔗

template<class Duration>
  requires three_way_comparable_with<sys_seconds, sys_time<Duration>>
  constexpr auto operator<=>(const leap_second& x, const sys_time<Duration>& y) noexcept;

Returns: x.date() <=> y.

30.11.9 Class time_zone_link [time.zone.link]

30.11.9.1 Overview [time.zone.link.overview]

namespace std::chrono { class time_zone_link { public: time_zone_link(time_zone_link&&) = default; time_zone_link& operator=(time_zone_link&&) = default; // unspecified additional constructors string_view name() const noexcept; string_view target() const noexcept; }; }

A time_zone_link specifies an alternative name for a time_zone.

time_zone_links are constructed when the time zone database is initialized.

30.11.9.2 Member functions [time.zone.link.members]

🔗

string_view name() const noexcept;

Returns: The alternative name for the time zone.

🔗

string_view target() const noexcept;

Returns: The name of the time_zone for which this time_zone_link provides an alternative name.

30.11.9.3 Non-member functions [time.zone.link.nonmembers]

🔗

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

Returns: x.name() == y.name().

🔗

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

Returns: x.name() <=> y.name().

30.12 Formatting [time.format]

Each formatter ([format.formatter]) specialization in the chrono library ([time.syn]) meets the Formatter requirements ([formatter.requirements]).

The parse member functions of these formatters interpret the format specification as a chrono-format-spec according to the following syntax:

chrono-format-spec :
fill-and-align

_{o p t}

width

_{o p t}

precision

_{o p t}

_{o p t}

chrono-specs

_{o p t}

chrono-specs :
conversion-spec
chrono-specs conversion-spec
chrono-specs literal-char

literal-char :
any character other than {, }, or %

conversion-spec :
% modifier

_{o p t}

type

modifier : one of
E O

type : one of
a A b B c C d D e F g G h H I j m M n
p q Q r R S t T u U V w W x X y Y z Z %

The productions fill-and-align, width, and precision are described in [format.string].

Giving a precision specification in the chrono-format-spec is valid only for types that are specializations of std::chrono::duration for which the nested typedef-name rep denotes a floating-point type.

For all other types, an exception of type format_error is thrown if the chrono-format-spec contains a precision specification.

All ordinary multibyte characters represented by literal-char are copied unchanged to the output.

A formatting locale is an instance of locale used by a formatting function, defined as

(2.1)
the "C" locale if the L option is not present in chrono-format-spec, otherwise
(2.2)
the locale passed to the formatting function if any, otherwise
(2.3)
the global locale.

Each conversion specifier conversion-spec is replaced by appropriate characters as described in Table 128; the formats specified in ISO 8601-1:2019 shall be used where so described.

Some of the conversion specifiers depend on the formatting locale.

If the string literal encoding is a Unicode encoding form and the locale is among an implementation-defined set of locales, each replacement that depends on the locale is performed as if the replacement character sequence is converted to the string literal encoding.

If the formatted object does not contain the information the conversion specifier refers to, an exception of type format_error is thrown.

The result of formatting a std::chrono::duration instance holding a negative value, or an hh_mm_ss object h for which h.is_negative() is true, is equivalent to the output of the corresponding positive value, with a STATICALLY-WIDEN<charT>("-") character sequence placed before the replacement of the initial conversion specifier.

[Example 1: cout << format("{:%T}", -10'000s); // prints: -02:46:40 cout << format("{:%H:%M:%S}", -10'000s); // prints: -02:46:40 cout << format("minutes {:%M, hours %H, seconds %S}", -10'000s); // prints: minutes -46, hours 02, seconds 40 — end example]

Unless explicitly requested, the result of formatting a chrono type does not contain time zone abbreviation and time zone offset information.

If the information is available, the conversion specifiers %Z and %z will format this information (respectively).

[Note 1:

If the information is not available and a %Z or %z conversion specifier appears in the chrono-format-spec, an exception of type format_error is thrown, as described above.

— end note]

If the type being formatted does not contain the information that the format flag needs, an exception of type format_error is thrown.

[Example 2:

A duration does not contain enough information to format as a weekday.

— end example]

However, if a flag refers to a “time of day” (e.g., %H, %I, %p, etc.)

, then a specialization of duration is interpreted as the time of day elapsed since midnight.

Table 128 — Meaning of conversion specifiers [tab:time.format.spec]

🔗 Specifier	Replacement
🔗 %a	The locale's abbreviated weekday name. If the value does not contain a valid weekday, an exception of type format_error is thrown.
🔗 %A	The locale's full weekday name. If the value does not contain a valid weekday, an exception of type format_error is thrown.
🔗 %b	The locale's abbreviated month name. If the value does not contain a valid month, an exception of type format_error is thrown.
🔗 %B	The locale's full month name. If the value does not contain a valid month, an exception of type format_error is thrown.
🔗 %c	The locale's date and time representation. The modified command %Ec produces the locale's alternate date and time representation.
🔗 %C	The year divided by 100 using floored division. If the result is a single decimal digit, it is prefixed with 0. The modified command %EC produces the locale's alternative representation of the century.
🔗 %d	The day of month as a decimal number. If the result is a single decimal digit, it is prefixed with 0. The modified command %Od produces the locale's alternative representation.
🔗 %D	Equivalent to %m/%d/%y.
🔗 %e	The day of month as a decimal number. If the result is a single decimal digit, it is prefixed with a space. The modified command %Oe produces the locale's alternative representation.
🔗 %F	Equivalent to %Y-%m-%d.
🔗 %g	The last two decimal digits of the calendar year as specified in ISO 8601-1:2019 for the week calendar. If the result is a single digit it is prefixed by 0.
🔗 %G	The calendar year as a decimal number, as specified in ISO 8601-1:2019 for the week calendar. If the result is less than four digits it is left-padded with 0 to four digits.
🔗 %h	Equivalent to %b.
🔗 %H	The hour (24-hour clock) as a decimal number. If the result is a single digit, it is prefixed with 0. The modified command %OH produces the locale's alternative representation.
🔗 %I	The hour (12-hour clock) as a decimal number. If the result is a single digit, it is prefixed with 0. The modified command %OI produces the locale's alternative representation.
🔗 %j	If the type being formatted is a specialization of duration, the decimal number of days without padding. Otherwise, the day of the year as a decimal number. January 1 is 001. If the result is less than three digits, it is left-padded with 0 to three digits.
🔗 %m	The month as a decimal number. Jan is 01. If the result is a single digit, it is prefixed with 0. The modified command %Om produces the locale's alternative representation.
🔗 %M	The minute as a decimal number. If the result is a single digit, it is prefixed with 0. The modified command %OM produces the locale's alternative representation.
🔗 %n	A new-line character.
🔗 %p	The locale's equivalent of the AM/PM designations associated with a 12-hour clock.
🔗 %q	The duration's unit suffix as specified in [time.duration.io].
🔗 %Q	The duration's numeric value (as if extracted via .count()).
🔗 %r	The locale's 12-hour clock time.
🔗 %R	Equivalent to %H:%M.
🔗 %S	Seconds as a decimal number. If the number of seconds is less than 10, the result is prefixed with 0. If the precision of the input cannot be exactly represented with seconds, then the format is a decimal floating-point number with a fixed format and a precision matching that of the precision of the input (or to a microseconds precision if the conversion to floating-point decimal seconds cannot be made within 18 fractional digits). The character for the decimal point is localized according to the locale. The modified command %OS produces the locale's alternative representation.
🔗 %t	A horizontal-tab character.
🔗 %T	Equivalent to %H:%M:%S.
🔗 %u	The calendar day of week as a decimal number (1-7), as specified in ISO 8601-1:2019, where Monday is 1. The modified command %Ou produces the locale's alternative representation.
🔗 %U	The week number of the year as a decimal number. The first Sunday of the year is the first day of week 01. Days of the same year prior to that are in week 00. If the result is a single digit, it is prefixed with 0. The modified command %OU produces the locale's alternative representation.
🔗 %V	The calendar week of year as a decimal number, as specified in ISO 8601-1:2019 for the week calendar. If the result is a single digit, it is prefixed with 0. The modified command %OV produces the locale's alternative representation.
🔗 %w	The weekday as a decimal number (0-6), where Sunday is 0. The modified command %Ow produces the locale's alternative representation.
🔗 %W	The week number of the year as a decimal number. The first Monday of the year is the first day of week 01. Days of the same year prior to that are in week 00. If the result is a single digit, it is prefixed with 0. The modified command %OW produces the locale's alternative representation.
🔗 %x	The locale's date representation. The modified command %Ex produces the locale's alternate date representation.
🔗 %X	The locale's time representation. The modified command %EX produces the locale's alternate time representation.
🔗 %y	The last two decimal digits of the year. If the result is a single digit it is prefixed by 0. The modified command %Oy produces the locale's alternative representation. The modified command %Ey produces the locale's alternative representation of offset from %EC (year only).
🔗 %Y	The year as a decimal number. If the result is less than four digits it is left-padded with 0 to four digits. The modified command %EY produces the locale's alternative full year representation.
🔗 %z	The offset from UTC as specified in ISO 8601-1:2019, 5.3.4.1. For example -0430 refers to 4 hours 30 minutes behind UTC. If the offset is zero, +0000 is used. The modified commands %Ez and %Oz insert a : between the hours and minutes: -04:30. If the offset information is not available, an exception of type format_error is thrown.
🔗 %Z	The time zone abbreviation. If the time zone abbreviation is not available, an exception of type format_error is thrown.
🔗 %%	A % character.

If the chrono-specs is omitted, the chrono object is formatted as if by streaming it to basic_ostringstream<charT> os with the formatting locale imbued and copying os.str() through the output iterator of the context with additional padding and adjustments as specified by the format specifiers.

[Example 3: string s = format("{:=>8}", 42ms); // value of s is "====42ms" — end example]

For chrono::duration the library only provides the following specialization of enable_nonlocking_formatter_optimization: template<class Rep, class Period> constexpr bool enable_nonlocking_formatter_optimization< chrono::duration<Rep, Period>> = enable_nonlocking_formatter_optimization<Rep>;

For chrono::zoned_time the library only provides the following specialization of enable_nonlocking_formatter_optimization: template<class Duration> constexpr bool enable_nonlocking_formatter_optimization< chrono::zoned_time<Duration, const std::chrono::time_zone*>> = true;

🔗

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

Remarks: If %Z is used, it is replaced with STATICALLY-WIDEN<charT>("UTC").

If %z (or a modified variant of %z) is used, an offset of 0min is formatted.

🔗

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

Remarks: If %Z is used, it is replaced with STATICALLY-WIDEN<charT>("UTC").

If %z (or a modified variant of %z) is used, an offset of 0min is formatted.

If the argument represents a time during a positive leap second insertion, and if a seconds field is formatted, the integral portion of that format is STATICALLY-WIDEN<charT>("60").

🔗

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

Remarks: If %Z is used, it is replaced with STATICALLY-WIDEN<charT>("TAI").

If %z (or a modified variant of %z) is used, an offset of 0min is formatted.

The date and time formatted are equivalent to those formatted by a sys_time initialized with sys_time<Duration>{tp.time_since_epoch()} - (sys_days{1970y/January/1} - sys_days{1958y/January/1})

🔗

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

Remarks: If %Z is used, it is replaced with STATICALLY-WIDEN<charT>("GPS").

If %z (or a modified variant of %z) is used, an offset of 0min is formatted.

The date and time formatted are equivalent to those formatted by a sys_time initialized with sys_time<Duration>{tp.time_since_epoch()} + (sys_days{1980y/January/Sunday[1]} - sys_days{1970y/January/1})

🔗

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

Remarks: If %Z is used, it is replaced with STATICALLY-WIDEN<charT>("UTC").

If %z (or a modified variant of %z) is used, an offset of 0min is formatted.

The date and time formatted are equivalent to those formatted by a sys_time initialized with clock_cast<system_clock>(t), or by a utc_time initialized with clock_cast<utc_clock>(t), where t is the first argument to format.

🔗

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

Remarks: If %Z, %z, or a modified version of %z is used, an exception of type format_error is thrown.

🔗

template<class Duration> struct local-time-format-t { // exposition only local_time<Duration> time; // exposition only const string* abbrev; // exposition only const seconds* offset_sec; // exposition only };

🔗

template<class Duration>
  local-time-format-t<Duration>
    local_time_format(local_time<Duration> time, const string* abbrev = nullptr,
                      const seconds* offset_sec = nullptr);

Returns: {time, abbrev, offset_sec}.

🔗

template<class Duration, class charT>
  struct formatter<chrono::local-time-format-t<Duration>, charT>;

Let f be a local-time-format-t<Duration> object passed to formatter::format.

Remarks: If the chrono-specs is omitted, the result is equivalent to using %F %T %Z as the chrono-specs.

If %Z is used, it is replaced with *f.abbrev if f.abbrev is not a null pointer value.

If %Z is used and f.abbrev is a null pointer value, an exception of type format_error is thrown.

If %z (or a modified variant of %z) is used, it is formatted with the value of *f.offset_sec if f.offset_sec is not a null pointer value.

If %z (or a modified variant of %z) is used and f.offset_sec is a null pointer value, then an exception of type format_error is thrown.

🔗

template<class Duration, class TimeZonePtr, class charT> struct formatter<chrono::zoned_time<Duration, TimeZonePtr>, charT> : formatter<chrono::local-time-format-t<common_type_t<Duration, seconds>>, charT> { template<class FormatContext> typename FormatContext::iterator format(const chrono::zoned_time<Duration, TimeZonePtr>& tp, FormatContext& ctx) const; };

🔗

template<class FormatContext>
  typename FormatContext::iterator
    format(const chrono::zoned_time<Duration, TimeZonePtr>& tp, FormatContext& ctx) const;

Effects: Equivalent to: sys_info info = tp.get_info(); return formatter<chrono::local-time-format-t<common_type_t<Duration, seconds>>, charT>:: format({tp.get_local_time(), &info.abbrev, &info.offset}, ctx);

30.13 Parsing [time.parse]

Each parse overload specified in this subclause calls from_stream unqualified, so as to enable argument-dependent lookup ([basic.lookup.argdep]).

In the following paragraphs, let is denote an object of type basic_istream<charT, traits> and let I be basic_istream<charT, traits>&, where charT and traits are template parameters in that context.

Recommended practice: Implementations should make it difficult to accidentally store or use a manipulator that may contain a dangling reference to a format string, for example by making the manipulators produced by parse immovable and preventing stream extraction into an lvalue of such a manipulator type.

🔗

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

Let F be fmt for the first overload and fmt.c_str() for the second overload.

Let traits be char_traits<charT> for the first overload.

Constraints: The expression from_stream(declval<basic_istream<charT, traits>&>(), F, tp) is well-formed when treated as an unevaluated operand .

Returns: A manipulator such that the expression is >> parse(fmt, tp) has type I, has value is, and calls from_stream(is, F, tp).

🔗

template<class charT, class traits, class Alloc, class Parsable>
  unspecified
    parse(const charT* fmt, Parsable& tp,
          basic_string<charT, traits, Alloc>& abbrev);
template<class charT, class traits, class Alloc, class Parsable>
  unspecified
    parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,
          basic_string<charT, traits, Alloc>& abbrev);

Let F be fmt for the first overload and fmt.c_str() for the second overload.

Constraints: The expression from_stream(declval<basic_istream<charT, traits>&>(), F, tp, addressof(abbrev)) is well-formed when treated as an unevaluated operand .

Returns: A manipulator such that the expression is >> parse(fmt, tp, abbrev) has type I, has value is, and calls from_stream(is, F, tp, addressof(abbrev)).

🔗

template<class charT, class Parsable>
  unspecified
    parse(const charT* fmt, Parsable& tp, minutes& offset);
template<class charT, class traits, class Alloc, class Parsable>
  unspecified
    parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,
          minutes& offset);

Let F be fmt for the first overload and fmt.c_str() for the second overload.

Let traits be char_traits<charT> and Alloc be allocator<charT> for the first overload.

Constraints: The expression from_stream(declval<basic_istream<charT, traits>&>(), F, tp, declval<basic_string<charT, traits, Alloc>*>(), &offset) is well-formed when treated as an unevaluated operand .

Returns: A manipulator such that the expression is >> parse(fmt, tp, offset) has type I, has value is, and calls: from_stream(is, F, tp, static_cast<basic_string<charT, traits, Alloc>*>(nullptr), &offset)

🔗

template<class charT, class traits, class Alloc, class Parsable>
  unspecified
    parse(const charT* fmt, Parsable& tp,
          basic_string<charT, traits, Alloc>& abbrev, minutes& offset);
template<class charT, class traits, class Alloc, class Parsable>
  unspecified
    parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,
          basic_string<charT, traits, Alloc>& abbrev, minutes& offset);

Let F be fmt for the first overload and fmt.c_str() for the second overload.

Constraints: The expression from_stream(declval<basic_istream<charT, traits>&>(), F, tp, addressof(abbrev), &offset) is well-formed when treated as an unevaluated operand .

Returns: A manipulator such that the expression is >> parse(fmt, tp, abbrev, offset) has type I, has value is, and calls from_stream(is, F, tp, addressof(abbrev), &offset).

All from_stream overloads behave as unformatted input functions, except that they have an unspecified effect on the value returned by subsequent calls to basic_istream<>::gcount().

Each overload takes a format string containing ordinary characters and flags which have special meaning.

Each flag begins with a %.

Some flags can be modified by E or O.

During parsing each flag interprets characters as parts of date and time types according to Table 129 .

Some flags can be modified by a width parameter given as a positive decimal integer called out as N below which governs how many characters are parsed from the stream in interpreting the flag.

All characters in the format string that are not represented in Table 129, except for whitespace, are parsed unchanged from the stream.

A whitespace character matches zero or more whitespace characters in the input stream.

If the type being parsed cannot represent the information that the format flag refers to, is.setstate(ios_base::failbit) is called.

[Example 1:

A duration cannot represent a weekday.

— end example]

However, if a flag refers to a “time of day” (e.g., %H, %I, %p, etc.)

, then a specialization of duration is parsed as the time of day elapsed since midnight.

If the from_stream overload fails to parse everything specified by the format string, or if insufficient information is parsed to specify a complete duration, time point, or calendrical data structure, setstate(ios_base::failbit) is called on the basic_istream.

Table 129 — Meaning of parse flags [tab:time.parse.spec]

🔗 Flag	Parsed value
🔗 %a	The locale's full or abbreviated case-insensitive weekday name.
🔗 %A	Equivalent to %a.
🔗 %b	The locale's full or abbreviated case-insensitive month name.
🔗 %B	Equivalent to %b.
🔗 %c	The locale's date and time representation. The modified command %Ec interprets the locale's alternate date and time representation.
🔗 %C	The century as a decimal number. The modified command %NC specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %EC interprets the locale's alternative representation of the century.
🔗 %d	The day of the month as a decimal number. The modified command %Nd specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %Od interprets the locale's alternative representation of the day of the month.
🔗 %D	Equivalent to %m/%d/%y.
🔗 %e	Equivalent to %d and can be modified like %d.
🔗 %F	Equivalent to %Y-%m-%d. If modified with a width N, the width is applied to only %Y.
🔗 %g	The last two decimal digits of the calendar year, as specified in ISO 8601-1:2019 for the week calendar. The modified command %Ng specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required.
🔗 %G	The calendar year as a decimal number, as specified in ISO 8601-1:2019 for the week calendar. The modified command %NG specifies the maximum number of characters to read. If N is not specified, the default is 4. Leading zeroes are permitted but not required.
🔗 %h	Equivalent to %b.
🔗 %H	The hour (24-hour clock) as a decimal number. The modified command %NH specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %OH interprets the locale's alternative representation.
🔗 %I	The hour (12-hour clock) as a decimal number. The modified command %NI specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %OI interprets the locale's alternative representation.
🔗 %j	If the type being parsed is a specialization of duration, a decimal number of days. Otherwise, the day of the year as a decimal number. January 1 is 1. In either case, the modified command %Nj specifies the maximum number of characters to read. If N is not specified, the default is 3. Leading zeroes are permitted but not required.
🔗 %m	The month as a decimal number. January is 1. The modified command %Nm specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %Om interprets the locale's alternative representation.
🔗 %M	The minutes as a decimal number. The modified command %NM specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %OM interprets the locale's alternative representation.
🔗 %n	Matches one whitespace character. [Note 1: %n, %t, and a space can be combined to match a wide range of whitespace patterns. For example, "%n " matches one or more whitespace characters, and "%n%t%t" matches one to three whitespace characters. — end note]
🔗 %p	The locale's equivalent of the AM/PM designations associated with a 12-hour clock.
🔗 %r	The locale's 12-hour clock time.
🔗 %R	Equivalent to %H:%M.
🔗 %S	The seconds as a decimal number. The modified command %NS specifies the maximum number of characters to read. If N is not specified, the default is 2 if the input time has a precision convertible to seconds. Otherwise the default width is determined by the decimal precision of the input and the field is interpreted as a long double in a fixed format. If encountered, the locale determines the decimal point character. Leading zeroes are permitted but not required. The modified command %OS interprets the locale's alternative representation.
🔗 %t	Matches zero or one whitespace characters.
🔗 %T	Equivalent to %H:%M:%S.
🔗 %u	The calendar day of week as a decimal number (1-7), as specified in ISO 8601-1:2019, where Monday is 1. The modified command %Nu specifies the maximum number of characters to read. If N is not specified, the default is 1. Leading zeroes are permitted but not required.
🔗 %U	The week number of the year as a decimal number. The first Sunday of the year is the first day of week 01. Days of the same year prior to that are in week 00. The modified command %NU specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %OU interprets the locale's alternative representation.
🔗 %V	The calendar week of year as a decimal number, as specified in ISO 8601-1:2019 for the week calendar. The modified command %NV specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required.
🔗 %w	The weekday as a decimal number (0-6), where Sunday is 0. The modified command %Nw specifies the maximum number of characters to read. If N is not specified, the default is 1. Leading zeroes are permitted but not required. The modified command %Ow interprets the locale's alternative representation.
🔗 %W	The week number of the year as a decimal number. The first Monday of the year is the first day of week 01. Days of the same year prior to that are in week 00. The modified command %NW specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command %OW interprets the locale's alternative representation.
🔗 %x	The locale's date representation. The modified command %Ex interprets the locale's alternate date representation.
🔗 %X	The locale's time representation. The modified command %EX interprets the locale's alternate time representation.
🔗 %y	The last two decimal digits of the year. If the century is not otherwise specified (e.g., with %C), values in the range [69, 99] are presumed to refer to the years 1969 to 1999, and values in the range [00, 68] are presumed to refer to the years 2000 to 2068. The modified command %Ny specifies the maximum number of characters to read. If N is not specified, the default is 2. Leading zeroes are permitted but not required. The modified commands %Ey and %Oy interpret the locale's alternative representation.
🔗 %Y	The year as a decimal number. The modified command %NY specifies the maximum number of characters to read. If N is not specified, the default is 4. Leading zeroes are permitted but not required. The modified command %EY interprets the locale's alternative representation.
🔗 %z	The offset from UTC in the format [+\|-]hh[mm]. For example -0430 refers to 4 hours 30 minutes behind UTC, and 04 refers to 4 hours ahead of UTC. The modified commands %Ez and %Oz parse a : between the hours and minutes and render leading zeroes on the hour field optional: [+\|-]h[h][:mm]. For example -04:30 refers to 4 hours 30 minutes behind UTC, and 4 refers to 4 hours ahead of UTC.
🔗 %Z	The time zone abbreviation or name. A single word is parsed. This word can only contain characters from the basic character set ([lex.charset]) that are alphanumeric, or one of '_', '/', '-', or '+'.
🔗 %%	A % character is extracted.

30.14 Hash support [time.hash]

🔗

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

The specialization hash<chrono::duration<Rep, Period>> is enabled ([unord.hash]) if and only if

hash<Rep> is enabled.

The member functions are not guaranteed to be noexcept.

🔗

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

The specialization hash<chrono::time_point<Clock, Duration>> is enabled ([unord.hash]) if and only if hash<Duration> is enabled.

The member functions are not guaranteed to be noexcept.

🔗

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>;

The specializations are enabled ([unord.hash]).

[Note 1:

All the hash<Key> specializations listed above meet the Cpp17Hash requirements, even when called on objects k of type Key such that k.ok() is false.

— end note]

🔗

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

The specialization hash<chrono::zoned_time<Duration, TimeZonePtr>> is enabled ([unord.hash]) if and only if hash<Duration> is enabled and hash<TimeZonePtr> is enabled.

The member functions are not guaranteed to be noexcept.

🔗

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

The specialization is enabled ([unord.hash]).

30.15 Header <ctime> synopsis [ctime.syn]

🔗

#define NULL see [support.types.nullptr] #define CLOCKS_PER_SEC see below #define TIME_UTC see below namespace std { using size_t = see [support.types.layout]; using clock_t = see below; using time_t = see below; struct timespec; struct tm; clock_t clock(); double difftime(time_t time1, time_t time0); time_t mktime(tm* timeptr); time_t time(time_t* timer); int timespec_get(timespec* ts, int base); char* asctime(const tm* timeptr); char* ctime(const time_t* timer); tm* gmtime(const time_t* timer); tm* localtime(const time_t* timer); size_t strftime(char* s, size_t maxsize, const char* format, const tm* timeptr); }

The contents of the header <ctime> are the same as the C standard library header <time.h>.258

The functions asctime, ctime, gmtime, and localtime are not required to avoid data races ([res.on.data.races]).