Date and time library
From cppreference.com
< cpp
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).
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) |
(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) |
[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) |
(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) |
[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]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) |
(C++20) | translates between a 12h/24h format time of day (function) |
[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) |
(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 nthweekday 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 nthweekday 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 nthweekday 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) |
[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) |
(C++20) | represents a linked list of tzdb (class) |
| 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) |
[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) |
(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) |
[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]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.constauto start{std::chrono::steady_clock::now()};constauto fb{Fibonacci(42)};constauto finish{std::chrono::steady_clock::now()};conststd::chrono::duration<double> elapsed_seconds{finish - start}; std::cout<<"Fibonacci(42): "<< fb <<"\nElapsed time: ";// std::cout << elapsed_seconds.count() << "s\n"; // Before C++20std::cout<< elapsed_seconds <<'\n';// C++20's chrono::duration operator<< // Prints UTC and local time.constauto 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
