Date and time utilities
C++ includes support for two types of time manipulation:
- The
chronolibrary, 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> |
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|---|---|
Defined in namespace std::chrono |
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(C++11)
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wall clock time from the system-wide realtime clock (class) |
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(C++11)
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monotonic clock that will never be adjusted (class) |
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(C++11)
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the clock with the shortest tick period available (class) |
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(C++20)
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determines if a type is a Clock (class template) (variable template) |
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(C++20)
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Clock for Coordinated Universal Time (UTC) (class) |
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(C++20)
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Clock for International Atomic Time (TAI) (class) |
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(C++20)
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Clock for GPS time (class) |
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(C++20)
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Clock used for file time (typedef) |
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(C++20)
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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> |
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|---|---|
Defined in namespace std::chrono |
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(C++11)
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a point in time (class template) |
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(C++20)
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traits class defining how to convert time points of one clock to another (class template) |
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(C++20)
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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> |
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|---|---|
Defined in namespace std::chrono |
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(C++11)
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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> |
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|---|---|
Defined in namespace std::chrono |
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(C++20)
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represents a time of day (class template) |
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(C++20)
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translates between a 12h/24h format time of day (function) |
Calendar
Defined in header <chrono> |
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|---|---|
Defined in namespace std::chrono |
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(C++20)
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tag class indicating the last day or weekday in a month (class) |
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(C++20)
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represents a day of a month (class) |
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(C++20)
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represents a month of a year (class) |
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(C++20)
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represents a year in the Gregorian calendar (class) |
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(C++20)
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represents a day of the week in the Gregorian calendar (class) |
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(C++20)
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represents the n-th weekday of a month (class) |
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(C++20)
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represents the last weekday of a month (class) |
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(C++20)
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represents a specific day of a specific month (class) |
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(C++20)
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represents the last day of a specific month (class) |
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(C++20)
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represents the n-th weekday of a specific month (class) |
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(C++20)
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represents the last weekday of a specific month (class) |
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(C++20)
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represents a specific month of a specific year (class) |
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(C++20)
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represents a specific year, month, and day (class) |
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(C++20)
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represents the last day of a specific year and month (class) |
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(C++20)
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represents the n-th weekday of a specific year and month (class) |
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(C++20)
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represents the last weekday of a specific year and month (class) |
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(C++20)
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conventional syntax for Gregorian calendar date creation (function) |
Time zone
Defined in header <chrono> |
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|---|---|
Defined in namespace std::chrono |
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(C++20)
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describes a copy of the IANA time zone database (class) |
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(C++20)
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represents a linked list of tzdb (class) |
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(C++20)
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accesses and controls the global time zone database information (function) |
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(C++20)
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locates a time_zone based on its name (function) |
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(C++20)
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returns the current time_zone (function) |
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(C++20)
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represents a time zone (class) |
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(C++20)
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represents information about a time zone at a particular time point (class) |
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(C++20)
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represents information about a local time to UNIX time conversion (class) |
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(C++20)
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selects how an ambiguous local time should be resolved (enum) |
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(C++20)
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traits class for time zone pointers used by zoned_time (class template) |
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(C++20)
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represents a time zone and a time point (class) |
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(C++20)
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contains information about a leap second insertion (class) |
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(C++20)
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leap second insertion information (class) |
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(C++20)
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obtains leap second insertion information from a utc_time object (function template) |
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(C++20)
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represents an alternative name for a time zone (class) |
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(C++20)
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exception thrown to report that a local time is nonexistent (class) |
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(C++20)
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exception thrown to report that a local time is ambiguous (class) |
chrono I/O
Defined in header <chrono> |
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|---|---|
Defined in namespace std::chrono |
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(C++20)
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parses a chrono object from a stream (function template) |
Notes
Feature testing macro: __cpp_lib_chrono (for std::chrono library).
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:
#include <iostream>
#include <chrono>
long fibonacci(unsigned n)
{
if (n < 2) return n;
return fibonacci(n-1) + fibonacci(n-2);
}
int main()
{
auto start = std::chrono::steady_clock::now();
std::cout << "f(42) = " << fibonacci(42) << '\n';
auto end = std::chrono::steady_clock::now();
std::chrono::duration<double> elapsed_seconds = end-start;
std::cout << "elapsed time: " << elapsed_seconds.count() << "s\n";
}
Possible output:
f(42) = 267914296 elapsed time: 1.88232s
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