Date and time utilities

 

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Library feature-test macros
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
integer_sequence (C++14)
Relational operators (deprecated)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Elementary string conversions
to_chars (C++17)
from_chars (C++17)
chars_format (C++17)
Type operations
declval (C++11)
as_const (C++17)

 

Date and time utilities

duration (C++11) time_point (C++11) time_of_day (C++20)	clock_time_conversion (C++20) clock_cast (C++20)
Clocks
system_clock (C++11) steady_clock (C++11) high_resolution_clock (C++11) is_clock (C++20)	utc_clock (C++20) tai_clock (C++20) gps_clock (C++20) file_clock (C++20) local_t (C++20)
Calendars
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)
Time zones
tzdb (C++20) tzdb_list (C++20) get_tzdbget_tzdb_listreload_tzdbremote_version (C++20)(C++20)(C++20)(C++20)	time_zone (C++20) locate_zone (C++20) current_zone (C++20) zoned_time (C++20) link (C++20) leap (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 main types as well as utility functions and common typedefs.

• clocks
• time points
• durations

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 (class)
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

time_of_day 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
time_of_day (C++20)	represents a time of day (class template)

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 n-th 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 n-th 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 n-th 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 (C++20)	contains information about a leap second insertion (class)
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)

chrono I/O

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

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

This example displays information about the execution time of a function call:

Run this code

#include <iostream>
#include <chrono>
#include <ctime>
 
long fibonacci(unsigned n)
{
    if (n < 2) return n;
    return fibonacci(n-1) + fibonacci(n-2);
}
 
int main()
{
    auto start = std::chrono::system_clock::now();
    std::cout << "f(42) = " << fibonacci(42) << '\n';
    auto end = std::chrono::system_clock::now();
 
    std::chrono::duration<double> elapsed_seconds = end-start;
    std::time_t end_time = std::chrono::system_clock::to_time_t(end);
 
    std::cout << "finished computation at " << std::ctime(&end_time)
              << "elapsed time: " << elapsed_seconds.count() << "s\n";
}

Possible output:

f(42) = 267914296
finished computation at Mon Oct  2 00:59:08 2017
elapsed time: 1.88232s