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).
- C-style date and time library (e.g. std::time)
chrono library defines three main types (durations, clocks, and time points) as well as utility functions and common typedefs.
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.
|| a time interval |
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:
|| wall clock time from the system-wide realtime clock |
|| monotonic clock that will never be adjusted |
|| the clock with the shortest tick period available |
A time point is a duration of time that has passed since the epoch of specific clock.
|| a point in time |
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:
long fibonacci(unsigned n)
if (n < 2) return n;
return fibonacci(n-1) + fibonacci(n-2);
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";
f(42) = 267914296
finished computation at Mon Jul 29 08:41:09 2013
elapsed time: 0.670427s