Using chrono, how should time be stored as a variable?

Question

I'm using Chrono to standardize the usage of timestamps in an application.

Given a timestamp, I would create a timepoint. I'd then convert it to time_t to pass it as a parameter.

std::chrono::system_clock::to_time_t (timePoint)

Should I be passing a timepoint instead? What seems to be best practice?

void func(time_t time)

or

void func(std::chrono::time_point timePoint)

Answer 1

My advice is that unless you have to drop down to the C API (e.g. time_t) for compatibility with some other code that uses it, just stay in <chrono> (e.g. std::chrono::system_clock::time_point). It has better precision, and is a unique type with the semantics "time point" instead of just an integral type.

That is, my vote is:

void func(std::chrono::system_clock::time_point timePoint);

C++20 will bring many facilities to make it easier to work with the <chrono> types, and those facilities are prototyped in a free open source library:

https://github.com/HowardHinnant/date

Note I slightly altered your suggestion. std::chrono::time_point is a class template, not a type:

template<class Clock, class Duration = typename Clock::duration>
    class time_point;

I chose system_clock as that is the clock that is analogous to the C type time_t. It counts time since since 1970-01-01 00:00:00 UTC, except at a higher precision than time_t typically does.

And system_clock::time_point is a type alias for time_point<system_clock> (you could use either).

For a video tutorial on <chrono>, see: https://www.youtube.com/watch?v=P32hvk8b13M