Defined in header <chrono>
template <class ToDuration, class Clock, class Duration>
constexpr std::chrono::time_point<Clock, ToDuration>
    floor(const std::chrono::time_point<Clock, Duration>& tp);
(since C++17)

Returns the largest time point t representable in ToDuration that is smaller or equal to tp.

The function does not participate in the overload resolution unless ToDuration is a specialization of std::chrono::duration.


tp - time point to round down

Return value

tp rounded down to the next time point using duration of type ToDuration.

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 Clock, class FromDuration,
          class = std::enable_if_t<detail::is_duration_v<To>>>
constexpr std::chrono::time_point<Clock, To>
    floor(const std::chrono::time_point<Clock, FromDuration>& tp)
    return std::chrono::time_point<Clock, To>{


#include <chrono>
#include <iostream>
#include <string>
template <typename TimePoint>
std::string to_string(const TimePoint& time_point)
    return std::to_string(time_point.time_since_epoch().count());
int main()
    using namespace std::literals::chrono_literals;
    using Sec = std::chrono::seconds;
    std::cout << "Time point\t" "Cast\t" "Floor\t" "Round\t" "Ceil\n";
    std::cout << "(ms)\t\t"     "(s)\t"  "(s)\t"   "(s)\t"   "(s)\n";
    for (const auto value_ms: {5432ms, 5678ms})
        std::chrono::time_point<std::chrono::system_clock, std::chrono::milliseconds>
            << to_string(time_point_ms) << "\t\t"
            << to_string(std::chrono::time_point_cast<Sec>(time_point_ms)) << "\t"
            << to_string(std::chrono::floor          <Sec>(time_point_ms)) << "\t"
            << to_string(std::chrono::round          <Sec>(time_point_ms)) << "\t"
            << to_string(std::chrono::ceil           <Sec>(time_point_ms)) << "\n";


Time point        Cast        Floor        Round        Ceil
(ms)                (s)        (s)        (s)        (s)
5432                5        5        5        6
5678                5        5        6        6

See also

converts a time point to another time point on the same clock, with a different duration
(function template)
converts a time_point to another, rounding up
(function template)
converts a time_point to another, rounding to nearest, ties to even
(function template)
converts a duration to another, rounding down
(function template)
nearest integer not greater than the given value

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