C++ includes support for two types of time manipulation:
chrono library, a flexible collection of types that track time with varying degrees of precision (e.g. std::chrono::time_point). std::time). std::chrono library
The chrono library defines three main types as well as utility functions and common typedefs:
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) | wall clock time from the system-wide realtime clock (class) |
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(C++11) | monotonic clock that will never be adjusted (class) |
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(C++11) | the clock with the shortest tick period available (class) |
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(C++20) | determines if a type is a Clock (class template) (variable template) |
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(C++20) | Clock for Coordinated Universal Time (UTC) (class) |
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(C++20) | Clock for International Atomic Time (TAI) (class) |
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(C++20) | Clock for GPS time (class) |
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(C++20) | Clock used for file time (typedef) |
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(C++20) | pseudo-clock representing local time (class) |
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) | a point in time (class template) |
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(C++20) | traits class defining how to convert time points of one clock to another (class template) |
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(C++20) | convert time points of one clock to another (function template) |
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) | a time interval (class template) |
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) | represents a time of day (class template) |
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(C++20) | translates between a 12h/24h format time of day (function) |
Defined in header <chrono> |
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Defined in namespace std::chrono |
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(C++20) | tag class indicating the last day or weekday in a month (class) |
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(C++20) | represents a day of a month (class) |
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(C++20) | represents a month of a year (class) |
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(C++20) | represents a year in the Gregorian calendar (class) |
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(C++20) | represents a day of the week in the Gregorian calendar (class) |
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(C++20) | represents the n-th weekday of a month (class) |
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(C++20) | represents the last weekday of a month (class) |
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(C++20) | represents a specific day of a specific month (class) |
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(C++20) | represents the last day of a specific month (class) |
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(C++20) | represents the n-th weekday of a specific month (class) |
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(C++20) | represents the last weekday of a specific month (class) |
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(C++20) | represents a specific month of a specific year (class) |
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(C++20) | represents a specific year, month, and day (class) |
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(C++20) | represents the last day of a specific year and month (class) |
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(C++20) | represents the n-th weekday of a specific year and month (class) |
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(C++20) | represents the last weekday of a specific year and month (class) |
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(C++20) | conventional syntax for Gregorian calendar date creation (function) |
Defined in header <chrono> |
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Defined in namespace std::chrono |
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(C++20) | describes a copy of the IANA time zone database (class) |
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(C++20) | represents a linked list of tzdb (class) |
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(C++20) | accesses and controls the global time zone database information (function) |
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(C++20) | locates a time_zone based on its name (function) |
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(C++20) | returns the current time_zone (function) |
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(C++20) | represents a time zone (class) |
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(C++20) | represents information about a time zone at a particular time point (class) |
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(C++20) | represents information about a local time to UNIX time conversion (class) |
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(C++20) | selects how an ambiguous local time should be resolved (enum) |
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(C++20) | traits class for time zone pointers used by zoned_time (class template) |
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(C++20) | represents a time zone and a time point (class) |
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(C++20) | contains information about a leap second insertion (class) |
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(C++20) | leap second insertion information (class) |
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(C++20) | obtains leap second insertion information from a utc_time object (function template) |
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(C++20) | represents an alternative name for a time zone (class) |
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(C++20) | exception thrown to report that a local time is nonexistent (class) |
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(C++20) | 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) | parses a chrono object from a stream (function template) |
| Feature-test macro | Value | Std | Comment |
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__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 |
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| 201907L | (C++20) | Calendars and Time Zones |
Also provided are the C-style date and time functions, such as std::time_t, std::difftime, and CLOCKS_PER_SEC.
This example displays information about the execution time of a function call:
#include <chrono>
#include <iostream>
long fibonacci(unsigned n)
{
if (n < 2)
return n;
return 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 << "f(42) = " << fb << '\n' << "elapsed time: ";
// std::cout << elapsed_seconds.count() << "s\n"; // Before C++20
std::cout << elapsed_seconds << '\n'; // C++20: operator<< chrono::duration
}Possible output:
f(42) = 267914296 elapsed time: 0.758056s
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