std::hash<std::chrono::time_point>

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Date and time library

Time point
time_point (C++11)
clock_time_conversion (C++20)
clock_cast (C++20)
Duration
duration (C++11)
Clocks
system_clock (C++11)
steady_clock (C++11)
is_clock (C++20)
utc_clock (C++20)
tai_clock (C++20)
high_resolution_clock (C++11)
gps_clock (C++20)
file_clock (C++20)
local_t (C++20)
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make12make24 (C++20)(C++20)
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Calendar
day (C++20)
month (C++20)
year (C++20)
weekday (C++20)
operator/ (C++20)
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year_month_day_last (C++20)
year_month_weekday (C++20)
year_month_weekday_last (C++20)
weekday_indexed (C++20)
weekday_last (C++20)
month_day (C++20)
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month_weekday (C++20)
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parse (C++20)

Time zone
tzdb (C++20)
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leap_second (C++20)
leap_second_info (C++20)
get_leap_second_info (C++20)
C-style date and time

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std::chrono::time_point

Member functions
time_point::time_point
time_point::time_since_epoch
time_point::operator+=time_point::operator-=
time_point::operator++time_point::operator-- (C++20)(C++20)
time_point::min
time_point::max
Non-member functions
operator+operator-
operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(C++20)
time_point_cast
floor (C++17)
ceil (C++17)
round (C++17)
Helper classes
common_type
hash<std::chrono::time_point> (C++26)

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Defined in header`<chrono>`
template<class Clock,class Duration> struct hash<std::chrono::time_point<Clock, Duration>>;		(since C++26)

The template specialization ofstd::hash forstd::chrono::time_point allows users to obtain hashes of objects of typestd::chrono::time_point<Clock, Duration>. This specialization isenabled if and only ifstd::hash<Duration> is enabled.

[edit]Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_chrono`	`202306L`	(C++26)	Hashing support for`std::chrono` value classes

Example

Run this code

#include <chrono>#include <cstddef>#include <iostream>#include <string>#include <thread>#include <unordered_map> struct my_system_clock:std::chrono::system_clock{using time_point=std::chrono::time_point<my_system_clock>; static time_point now()noexcept{return time_point{std::chrono::system_clock::now().time_since_epoch()};} template<class CharT,class Traits>friendauto operator<<(std::basic_ostream<CharT, Traits>& os,const time_point& tp)-> decltype(os){return os<< std::chrono::system_clock::time_point{tp.time_since_epoch()};}}; using my_system_clock_tp=std::chrono::time_point<my_system_clock>; #if __cpp_lib_chrono < 202306L// custom specialization of std::hash can be injected in namespace stdtemplate<>structstd::hash<my_system_clock_tp>{std::size_t operator()(const my_system_clock_tp& d)constnoexcept{return d.time_since_epoch().count();}};#endif int main(){usingnamespace std::chrono_literals; std::unordered_map<my_system_clock_tp,std::string> log; for(int i{}; i!=4;++i){std::this_thread::sleep_for(100ms);        log[my_system_clock::now()]="event #"+std::to_string(i);} for(autoconst&[time, message]: log)std::cout<<'['<< time<<"], message: "<< message<<'\n';}

Possible output:

[2024-03-22 10:47:14.966238436], message: event #3[2024-03-22 10:47:14.866096194], message: event #2[2024-03-22 10:47:14.765965786], message: event #1[2024-03-22 10:47:14.665817365], message: event #0