Date and time utilities

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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)


[edit] chrono library

The chrono library defines three main types (durations, clocks, and time points) as well as utility functions and common typedefs.

[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
a time interval
(class template) [edit]

[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 three clock types:

Defined in header <chrono>
Defined in namespace std::chrono
wall clock time from the system-wide realtime clock
(class) [edit]
monotonic clock that will never be adjusted
(class) [edit]
the clock with the shortest tick period available
(class) [edit]

[edit] Time point

A time point is a duration of time that has passed since the epoch of specific clock.

Defined in header <chrono>
Defined in namespace std::chrono
a point in time
(class template) [edit]

[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

This example displays information about the execution time of a function call:

#include <iostream>
#include <chrono>
#include <ctime>
long fibonacci(int n)
    if (n < 3) return 1;
    return fibonacci(n-1) + fibonacci(n-2);
int main()
    std::chrono::time_point<std::chrono::system_clock> start, end;
    start = std::chrono::system_clock::now();
    std::cout << "f(42) = " << fibonacci(42) << '\n';
    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 Jul 29 08:41:09 2013
elapsed time: 0.670427s