mortie/chrono-cheat-sheet.md

## chrono-cheat-sheet.md

      
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              chrono-cheat-sheet.md
            
          
    Chrono cheat sheet

For the every-day programmer who needs to get shit done instead of fighting type errors.
If your application deals with times in any meaningful way, you should probably want to actually store time_points and durations and what-not; chrono has a pretty rich vocabulary for talking about time-related concepts using the type system. However, sometimes you just need to do something simple, like timing how long something takes, which is where chrono becomes overly complex, hence this cheat sheet.
All examples will assume #include <chrono>.
I just want to time something, then print the result

auto startTime = std::chrono::steady_clock::now();

/* something which might take time */

auto endTime = std::chrono::steady_clock::now();
auto duration = std::chrono::duration<double>(endTime - startTime);
std::cout << "It took " << duration.count() << " seconds.\n";
Alternatively, to print in milliseconds (or microseconds or gigaseconds or whatever):
auto startTime = std::chrono::steady_clock::now();

/* something which might take time */

auto endTime = std::chrono::steady_clock::now();
auto duration = std::chrono::duration<double, std::milli>(endTime - startTime); // or std::micro, std::giga, etc
std::cout << "It took " << duration.count() << " milliseconds.\n";
I just want to get a monotonically increasing time in seconds

This is what Python would call time.time().
double seconds = std::chrono::duration<double>(std::chrono::steady_clock::now().time_since_epoch()).count();
I just want to print a pretty datetime

In C++20, you should be able to do this:
std::cout << "Now: " << std::chrono::system_clock::now() << '\n';
However, until then you can convert it to a time_t and use ctime:
time_t now = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
std::cout << "Now: " << ctime(&now) << '\n';
(note that ctime isn't thread-safe. Use ctime_r if you need a thread-safe variant.)