Date and time utilities

 

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)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20)   bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17) to_chars_result (C++17) from_chars_result (C++17)

 

Date and time utilities

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)
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)
chrono I/O
parse (C++20)
C-style date and time

 

C++ includes support for two types of time manipulation:

• The chrono library, a flexible collection of types that track time with varying degrees of precision (e.g. std::chrono::time_point).
• C-style date and time library (e.g. std::time).

std::chrono library

The chrono library defines three(until C++20) five(since C++20) main types as well as utility functions and common typedefs:

• clocks,
• time points,
• durations,

calendar dates, time zone information.

(since C++20)

Clocks

A clock consists of a starting point (or epoch) and a tick rate. For example, a clock may have an epoch of January 1, 1970 and tick every second. C++ defines several clock types:

Defined in header <chrono>
Defined in namespace std::chrono
system_clock (C++11)	wall clock time from the system-wide realtime clock (class)
steady_clock (C++11)	monotonic clock that will never be adjusted (class)
high_resolution_clock (C++11)	the clock with the shortest tick period available (class)
is_clockis_clock_v (C++20)	determines if a type is a Clock (class template) (variable template)
utc_clock (C++20)	Clock for Coordinated Universal Time (UTC) (class)
tai_clock (C++20)	Clock for International Atomic Time (TAI) (class)
gps_clock (C++20)	Clock for GPS time (class)
file_clock (C++20)	Clock used for file time (typedef)
local_t (C++20)	pseudo-clock representing local time (class)

Time point

A time point is a duration of time that has passed since the epoch of a specific clock.

Defined in header <chrono>
Defined in namespace std::chrono
time_point (C++11)	a point in time (class template)
clock_time_conversion (C++20)	traits class defining how to convert time points of one clock to another (class template)
clock_cast (C++20)	convert time points of one clock to another (function template)

Duration

A duration consists of a span of time, defined as some number of ticks of some time unit. For example, "42 seconds" could be represented by a duration consisting of 42 ticks of a 1-second time unit.

Defined in header <chrono>
Defined in namespace std::chrono
duration (C++11)	a time interval (class template)

Time of day

hh_mm_ss splits a duration representing time elapsed since midnight into hours, minutes, seconds, and fractional seconds, as applicable. It is primarily a formatting tool.

Defined in header <chrono>
Defined in namespace std::chrono
hh_mm_ss (C++20)	represents a time of day (class template)
is_amis_pmmake12make24 (C++20)	translates between a 12h/24h format time of day (function)

Calendar

Defined in header <chrono>
Defined in namespace std::chrono
last_spec (C++20)	tag class indicating the last day or weekday in a month (class)
day (C++20)	represents a day of a month (class)
month (C++20)	represents a month of a year (class)
year (C++20)	represents a year in the Gregorian calendar (class)
weekday (C++20)	represents a day of the week in the Gregorian calendar (class)
weekday_indexed (C++20)	represents the nth weekday of a month (class)
weekday_last (C++20)	represents the last weekday of a month (class)
month_day (C++20)	represents a specific day of a specific month (class)
month_day_last (C++20)	represents the last day of a specific month (class)
month_weekday (C++20)	represents the nth weekday of a specific month (class)
month_weekday_last (C++20)	represents the last weekday of a specific month (class)
year_month (C++20)	represents a specific month of a specific year (class)
year_month_day (C++20)	represents a specific year, month, and day (class)
year_month_day_last (C++20)	represents the last day of a specific year and month (class)
year_month_weekday (C++20)	represents the nth weekday of a specific year and month (class)
year_month_weekday_last (C++20)	represents the last weekday of a specific year and month (class)
operator/ (C++20)	conventional syntax for Gregorian calendar date creation (function)

Time zone

Defined in header <chrono>
Defined in namespace std::chrono
tzdb (C++20)	describes a copy of the IANA time zone database (class)
tzdb_list (C++20)	represents a linked list of tzdb (class)
get_tzdbget_tzdb_listreload_tzdbremote_version (C++20)	accesses and controls the global time zone database information (function)
locate_zone (C++20)	locates a time_zone based on its name (function)
current_zone (C++20)	returns the current time_zone (function)
time_zone (C++20)	represents a time zone (class)
sys_info (C++20)	represents information about a time zone at a particular time point (class)
local_info (C++20)	represents information about a local time to UNIX time conversion (class)
choose (C++20)	selects how an ambiguous local time should be resolved (enum)
zoned_traits (C++20)	traits class for time zone pointers used by zoned_time (class template)
zoned_time (C++20)	represents a time zone and a time point (class)
leap_second (C++20)	contains information about a leap second insertion (class)
leap_second_info (C++20)	leap second insertion information (class)
get_leap_second_info (C++20)	obtains leap second insertion information from a utc_time object (function template)
time_zone_link (C++20)	represents an alternative name for a time zone (class)
nonexistent_local_time (C++20)	exception thrown to report that a local time is nonexistent (class)
ambiguous_local_time (C++20)	exception thrown to report that a local time is ambiguous (class)

Literals

Defined in header <chrono>
Defined in inline namespace std::literals::chrono_literals
operator""y (C++20)	a std::chrono::year literal representing a particular year (function)
operator""d (C++20)	a std::chrono::day literal representing a day of a month (function)
operator""h (C++14)	a std::chrono::duration literal representing hours (function)
operator""min (C++14)	a std::chrono::duration literal representing minutes (function)
operator""s (C++14)	a std::chrono::duration literal representing seconds (function)
operator""ms (C++14)	a std::chrono::duration literal representing milliseconds (function)
operator""us (C++14)	a std::chrono::duration literal representing microseconds (function)
operator""ns (C++14)	a std::chrono::duration literal representing nanoseconds (function)

chrono I/O

Defined in header <chrono>
Defined in namespace std::chrono
parse (C++20)	parses a chrono object from a stream (function template)

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_chrono	201510L	(C++17)	Rounding functions for std::chrono::duration and std::chrono::time_point
	201611L	(C++17)	constexpr for all the member functions of std::chrono::duration and std::chrono::time_point
	201907L	(C++20)	Calendars and Time zones
	202306L	(C++26)	Hashing support for std::chrono value classes

C-style date and time library

Also provided are the C-style date and time functions, such as std::time_t, std::difftime, and CLOCKS_PER_SEC.

Example

Measures and displays an execution time of a function call.

Run this code

#include <chrono>
#include <iostream>
 
long Fibonacci(unsigned n)
{
    return n < 2 ? n : Fibonacci(n - 1) + Fibonacci(n - 2);
}
 
int main()
{
    const auto start{std::chrono::steady_clock::now()};
    const auto fb{Fibonacci(42)};
    const auto end{std::chrono::steady_clock::now()};
    const std::chrono::duration<double> elapsed_seconds{end - start};
 
    std::cout << "Fibonacci(42): " << fb << "\nElapsed time: ";
//  std::cout << elapsed_seconds.count() << "s\n"; // Before C++20
    std::cout << elapsed_seconds << '\n'; // C++20's chrono::duration operator<<
}

Possible output:

Fibonacci(42): 267914296
Elapsed time: 0.791429s