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
)
chrono
library
The chrono
library defines three main types (durations, clocks, and time points) as well as utility functions and common typedefs.
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) |
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 | |
(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) |
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 | |
(C++11) | a point in time (class template) |
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> #include <ctime> long fibonacci(unsigned n) { if (n < 2) return n; 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
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