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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

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) Time of day is_amis_pm (C++20)(C++20) make12make24 (C++20)(C++20) hh_mm_ss (C++20)

Calendar day (C++20) month (C++20) year (C++20) weekday (C++20) operator/ (C++20) year_month_day (C++20) 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) month_day_last (C++20) month_weekday (C++20) month_weekday_last (C++20) year_month (C++20) last_speclast (C++20)(C++20) chrono I/O parse (C++20)

Time zone tzdb (C++20) tzdb_list (C++20) get_tzdbget_tzdb_listreload_tzdbremote_version (C++20)(C++20)(C++20)(C++20) sys_info (C++20) local_info (C++20) nonexistent_local_time (C++20) ambiguous_local_time (C++20) locate_zone (C++20) current_zone (C++20) time_zone (C++20) choose (C++20) zoned_traits (C++20) zoned_time (C++20) time_zone_link (C++20) leap_second (C++20) leap_second_info (C++20) get_leap_second_info (C++20) C-style date and time

 

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)

 

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

The template specialization of std::hash for std::chrono::time_point allows users to obtain hashes of objects of type std::chrono::time_point<Clock, Duration>. This specialization is enabled if and only if std::hash<Duration> is enabled.

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

See also

hash (C++11)

hash function object (class template)