Date and time utilities

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< cpp
 
C++
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)  
(C++11)

Relational operators (deprecated in C++20)
 
Date and time utilities
Time point
(C++11)
(C++20)
Duration
(C++11)
Clocks
(C++11)
(C++11)
(C++20)
(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)
Time zone
(C++20)
(C++20)
(C++20)(C++20)(C++20)(C++20)  
(C++20)
chrono I/O
(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
(C++11)
 wall clock time from the system-wide realtime clock
(class)
(C++11)
 monotonic clock that will never be adjusted
(class)
(C++11)
 the clock with the shortest tick period available
(class)
(C++20)
 determines if a type is a Clock
(class template) (variable template)
(C++20)
 Clock for Coordinated Universal Time (UTC)
(class)
(C++20)
 Clock for International Atomic Time (TAI)
(class)
(C++20)
 Clock for GPS time
(class)
(C++20)
 Clock used for file time
(typedef)
(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
(C++11)
 a point in time
(class template)
(C++20)
 traits class defining how to convert time points of one clock to another
(class template)
(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
(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
(C++20)
 represents a time of day
(class template)
(C++20)
 translates between a 12h/24h format time of day
(function)

Calendar

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

Time zone

Defined in header <chrono>
Defined in namespace std::chrono
(C++20)
 describes a copy of the IANA time zone database
(class)
(C++20)
 represents a linked list of tzdb
(class)
(C++20)
 accesses and controls the global time zone database information
(function)
(C++20)
 locates a time_zone based on its name
(function)
(C++20)
 returns the current time_zone
(function)
(C++20)
 represents a time zone
(class)
(C++20)
 represents information about a time zone at a particular time point
(class)
(C++20)
 represents information about a local time to UNIX time conversion
(class)
(C++20)
 selects how an ambiguous local time should be resolved
(enum)
(C++20)
 traits class for time zone pointers used by zoned_time
(class template)
(C++20)
 represents a time zone and a time point
(class)
(C++20)
 contains information about a leap second insertion
(class)
(C++20)
 leap second insertion information
(class)
(C++20)
 obtains leap second insertion information from a utc_time object
(function template)
(C++20)
 represents an alternative name for a time zone
(class)
(C++20)
 exception thrown to report that a local time is nonexistent
(class)
(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
(C++20)
 a std::chrono::year literal representing a particular year
(function)
(C++20)
 a std::chrono::day literal representing a day of a month
(function)
(C++14)
 a std::chrono::duration literal representing hours
(function)
(C++14)
 a std::chrono::duration literal representing minutes
(function)
(C++14)
 a std::chrono::duration literal representing seconds
(function)
(C++14)
 a std::chrono::duration literal representing milliseconds
(function)
(C++14)
 a std::chrono::duration literal representing microseconds
(function)
(C++14)
 a std::chrono::duration literal representing nanoseconds
(function)

chrono I/O

Defined in header <chrono>
Defined in namespace std::chrono
(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
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