std::chrono...o::duration)(3)

💖 std::chrono::round(std::chrono::duration) 💖

okay so this page is from the C++ Standard Libary manual — yes, that's the manual name — and its page title is literally std::chrono...o::duration)(3). It's the C++ Standard Library bestie for rounding a duration to the nearest ToDuration, with ties going to even. no cap, that's the whole vibe.

🌸 NAME 🌸

std::chrono::round(std::chrono::duration) — std::chrono::round(std::chrono::duration)

✨ Synopsis ✨

Defined in header <chrono>

template< class ToDuration, class Rep, class Period >
constexpr ToDuration round( const std::chrono::duration<Rep, Period>& d );

(since C++17)

Returns the value t representable in ToDuration that is the closest to d. If there are two such values, returns the even value (that is, the value t such that t % 2 == 0).

The function does not participate in the overload resolution unless ToDuration is a specialization of std::chrono::duration and std::chrono::treat_as_floating_point_v<typename ToDuration::rep> is false.

🎀 Parameters 🎀

• d — duration to convert

🦋 Return value 🦋

d rounded to the nearest duration of type ToDuration, rounding to even in halfway cases.

🧚 Possible implementation 🧚

namespace detail
{
    template<class> inline constexpr bool is_duration_v = false;
    template<class Rep, class Period> inline constexpr bool is_duration_v<
        std::chrono::duration<Rep, Period>> = true;
}

template<class To, class Rep, class Period,
         class = std::enable_if_t<detail::is_duration_v<To> &&
                !std::chrono::treat_as_floating_point_v<typename To::rep>>>
constexpr To round(const std::chrono::duration<Rep, Period>& d)
{
    To t0 = std::chrono::floor<To>(d);
    To t1 = t0 + To{1};
    auto diff0 = d - t0;
    auto diff1 = t1 - d;
    if (diff0 == diff1)
    {
        if (t0.count() & 1)
            return t1;
        return t0;
    }
    else if (diff0 < diff1)
        return t0;
    return t1;
}

🌈 Example 🌈

// Run this code

#include <chrono>
#include <iomanip>
#include <iostream>

int main()
{
    using namespace std::chrono_literals;
    std::cout << "Duration\tFloor\tRound\tCeil\n";
    for (using Sec = std::chrono::seconds;
        auto const d : {+4999ms, +5000ms, +5001ms, +5499ms, +5500ms, +5999ms,
                        -4999ms, -5000ms, -5001ms, -5499ms, -5500ms, -5999ms})
        std::cout << std::showpos << d << "\t\t"
                  << std::chrono::floor<Sec>(d) << '\t'
                  << std::chrono::round<Sec>(d) << '\t'
                  << std::chrono::ceil <Sec>(d) << '\n';
}

💻 Output: 💻

Duration        Floor   Round   Ceil
+4999ms         +4s     +5s     +5s
+5000ms         +5s     +5s     +5s
+5001ms         +5s     +5s     +6s
+5499ms         +5s     +5s     +6s
+5500ms         +5s     +6s     +6s
+5999ms         +5s     +6s     +6s
-4999ms         -5s     -5s     -4s
-5000ms         -5s     -5s     -5s
-5001ms         -6s     -5s     -5s
-5499ms         -6s     -5s     -5s
-5500ms         -6s     -6s     -5s
-5999ms         -6s     -6s     -5s

👀 See also 👀

• duration_cast (C++11) — converts a duration to another, with a different tick interval (function template)
• floor(std::chrono::duration) (C++17) — converts a duration to another, rounding down (function template)
• ceil(std::chrono::duration) (C++17) — converts a duration to another, rounding up (function template)
• round(std::chrono::time_point) (C++17) — converts a time_point to another, rounding to nearest, ties to even (function template)
• round, roundf, roundl, lround, lroundf, lroundl, llround, llroundf, llroundl (C++11) — nearest integer, rounding away from zero in halfway cases (function)

💖 that's the whole page, bestie — source: http://cppreference.com · version/date: 2024.06.10 · manual: std::chrono...o::duration)(3) 💖