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Date and time library

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< cpp
 
C++
 
Date and time library
Time point
(C++11)
(C++20)  
(C++20)
Duration
(C++11)
Clocks
(C++11)
(C++11)
(C++20)
(C++20)
(C++20)
(C++11)
(C++20)
(C++20)
(C++20)
Time of day
(C++20)(C++20)
(C++20)(C++20)
(C++20)
Calendar
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)  
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)(C++20)
chrono I/O
(C++20)

 

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

Contents

[edit] Chrono library (since C++11)

The chrono library defines several main types as well as utility functions and common typedefs:

(since C++20)

[edit] 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
(C++11)
 wall clock time from the system-wide realtime clock
(class) [edit]
(C++11)
 monotonic clock that will never be adjusted
(class) [edit]
(C++11)
 the clock with the shortest tick period available
(class) [edit]
(C++20)
 determines if a type is a Clock
(class template) (variable template)[edit]
(C++20)
 Clock for Coordinated Universal Time (UTC)
(class) [edit]
(C++20)
 Clock for International Atomic Time (TAI)
(class) [edit]
(C++20)
 Clock for GPS time
(class) [edit]
(C++20)
 Clock used for file time
(typedef) [edit]
(C++20)
 pseudo-clock representing local time
(class) [edit]

[edit] 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
(C++11)
 a point in time
(class template) [edit]
(C++20)
 traits class defining how to convert time points of one clock to another
(class template) [edit]
(C++20)
 convert time points of one clock to another
(function template) [edit]

[edit] 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
(C++11)
 a time interval
(class template) [edit]

[edit] Time of day (since C++20)

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
(C++20)
 represents a time of day
(class template) [edit]
(C++20)
 translates between a 12h/24h format time of day
(function) [edit]

[edit] Calendar (since C++20)

Defined in header <chrono>
Defined in namespace std::chrono
(C++20)
 tag class indicating the last day or weekday in a month
(class) [edit]
(C++20)
 represents a day of a month
(class) [edit]
(C++20)
 represents a month of a year
(class) [edit]
(C++20)
 represents a year in the Gregorian calendar
(class) [edit]
(C++20)
 represents a day of the week in the Gregorian calendar
(class) [edit]
(C++20)
 represents the nth weekday of a month
(class) [edit]
(C++20)
 represents the last weekday of a month
(class) [edit]
(C++20)
 represents a specific day of a specific month
(class) [edit]
(C++20)
 represents the last day of a specific month
(class) [edit]
(C++20)
 represents the nth weekday of a specific month
(class) [edit]
(C++20)
 represents the last weekday of a specific month
(class) [edit]
(C++20)
 represents a specific month of a specific year
(class) [edit]
(C++20)
 represents a specific year, month, and day
(class) [edit]
(C++20)
 represents the last day of a specific year and month
(class) [edit]
(C++20)
 represents the nth weekday of a specific year and month
(class) [edit]
(C++20)
 represents the last weekday of a specific year and month
(class) [edit]
(C++20)
 conventional syntax for Gregorian calendar date creation
(function) [edit]

[edit] Time zone (since C++20)

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

[edit] Literals (since C++14)

Defined in header <chrono>
Defined in inline namespace std::literals::chrono_literals
(C++20)
 a std::chrono::year literal representing a particular year
(function) [edit]
(C++20)
 a std::chrono::day literal representing a day of a month
(function) [edit]
(C++14)
 a std::chrono::duration literal representing hours
(function) [edit]
(C++14)
 a std::chrono::duration literal representing minutes
(function) [edit]
(C++14)
 a std::chrono::duration literal representing seconds
(function) [edit]
(C++14)
 a std::chrono::duration literal representing milliseconds
(function) [edit]
(C++14)
 a std::chrono::duration literal representing microseconds
(function) [edit]
(C++14)
 a std::chrono::duration literal representing nanoseconds
(function) [edit]

[edit] Chrono I/O (since C++20)

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

[edit] 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

[edit] 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.

[edit] Example

Run this code
#include <chrono>
#include <iostream>
 
long Fibonacci(unsigned n)
{
    return n < 2 ? n : Fibonacci(n - 1) + Fibonacci(n - 2);
}
 
int main()
{
    // Measures and displays an execution time of a function call.
    const auto start{std::chrono::steady_clock::now()};
    const auto fb{Fibonacci(42)};
    const auto finish{std::chrono::steady_clock::now()};
    const std::chrono::duration<double> elapsed_seconds{finish - 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<<
 
    // Prints UTC and local time.
    const auto tp_utc{std::chrono::system_clock::now()};
    std::cout << "Current time 'UTC' is: " << tp_utc << "\n"
                 "Current time 'Local' is: "
              << std::chrono::current_zone()->to_local(tp_utc) << '\n';
}

Possible output: 

Fibonacci(42): 267914296
Elapsed time: 0.728532s
Current time 'UTC' is: 2025-02-10 06:22:39.420666960
Current time 'Local' is: 2025-02-10 09:22:39.420666960
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