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)
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 three clock types:
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wall clock time from the system-wide realtime clock
(class) |
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monotonic clock that will never be adjusted
(class) |
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the clock with the shortest tick period available
(class) |
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determines if a type is a Clock
(class template) (variable template) |
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Clock for Coordinated Universal Time (UTC)
(class) |
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Clock for International Atomic Time (TAI)
(class) |
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Clock for GPS time
(class) |
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Clock used for file time
(class) |
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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.
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a point in time
(class template) |
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traits class defining how to convert time points of one clock to another
(class template) |
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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.
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a time interval
(class template) |
Time of day
time_of_day splits a duration representing time elapsed since midnight into hours, minutes, seconds, and fractional seconds, as applicable. It is primarily a formatting tool.
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represents a time of day
(class template) |
Calendar
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tag class indicating the last day or weekday in a month
(class) |
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represents a day of a month
(class) |
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represents a month of a year
(class) |
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represents a year in the Gregorian calendar
(class) |
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represents a day of the week in the Gregorian calendar
(class) |
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represents the n-th weekday of a month
(class) |
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represents the last weekday of a month
(class) |
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represents a specific day of a specific month
(class) |
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represents the last day of a specific month
(class) |
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represents the n-th weekday of a specific month
(class) |
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represents the last weekday of a specific month
(class) |
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represents a specific month of a specific year
(class) |
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represents a specific year, month, and day
(class) |
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represents the last day of a specific year and month
(class) |
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represents the n-th weekday of a specific year and month
(class) |
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represents the last weekday of a specific year and month
(class) |
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conventional syntax for Gregorian calendar date creation
(function) |
Time zone
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describes a copy of the IANA time zone database
(class) |
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represents a linked list of tzdb
(class) |
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accesses and controls the global time zone database information
(function) |
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locates a time_zone based on its name
(function) |
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returns the current time_zone
(function) |
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represents a time zone
(class) |
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represents information about a time zone at a particular time point
(class) |
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represents information about a local time to UNIX time conversion
(class) |
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represents a time zone and a time point
(class) |
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contains information about a leap second insertion
(class) |
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represents an alternative name for a time zone
(class) |
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exception thrown to report that a local time is nonexistent
(class) |
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exception thrown to report that a local time is ambiguous
(class) |
chrono I/O
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formats a streamable chrono object for insertion
(function template) |
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parses a chrono object from a stream
(function template) |
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>
#include <ctime>
long fibonacci(unsigned n)
{
if (n < 2) return n;
return fibonacci(n-1) + fibonacci(n-2);
}
int main()
{
auto start = std::chrono::system_clock::now();
std::cout << "f(42) = " << fibonacci(42) << '\n';
auto end = std::chrono::system_clock::now();
std::chrono::duration<double> elapsed_seconds = end-start;
std::time_t end_time = std::chrono::system_clock::to_time_t(end);
std::cout << "finished computation at " << std::ctime(&end_time)
<< "elapsed time: " << elapsed_seconds.count() << "s\n";
}Possible output:
f(42) = 267914296
finished computation at Mon Oct 2 00:59:08 2017
elapsed time: 1.88232s