How to format std::chrono durations?

Question

Is there a convenient way to format std::chrono::duration to a specified format?

std::chrono::high_resolution_clock::time_point now, then;
then          


        

Answer 1

Here is a possible solution using a variadic template.
The if constexpr () makes it c++17 only but replacing with a regular if still works and is c++14 compliant.

template
std::string formatDuration(DurationIn d)
{   
    auto val = std::chrono::duration_cast(d);

    string out = std::to_string(val.count());

    if constexpr(sizeof...(RestDurations) > 0) {
        out += "::" + formatDuration(d - val);
    }

    return out;
}

template
std::string formatDuration(DurationIn) { return {}; } // recursion termination

testing in main, outputs "77::600::42"

auto formattedStr = formatDuration<
    std::chrono::microseconds,
    std::chrono::seconds,
    std::chrono::milliseconds,
    std::chrono::microseconds>(77'600'042us);