< cpp‎ | chrono‎ | time point
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

Defined in header <chrono>
template< class ToDuration, class Clock, class Duration >

constexpr std::chrono::time_point<Clock, ToDuration>

    round( const std::chrono::time_point<Clock, Duration>& tp );
(since C++17)

Returns the nearest time point to tp representable in ToDuration, rounding to even in halfway cases.

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.


[edit] Parameters

tp - time point to round to nearest

[edit] Return value

tp rounded to nearest time point using duration of type ToDuration, rounding to even in halfway cases.

[edit] 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> &&
                !std::chrono::treat_as_floating_point_v<typename To::rep>>>
constexpr std::chrono::time_point<Clock, To> round(
    const std::chrono::time_point<Clock, FromDuration>& tp)
    return std::chrono::time_point<Clock, To>{

[edit] Example

#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

[edit] See also

converts a time point to another time point on the same clock, with a different duration
(function template) [edit]
converts a time_point to another, rounding up
(function template) [edit]
converts a time_point to another, rounding down
(function template) [edit]
converts a duration to another, rounding to nearest, ties to even
(function template) [edit]
nearest integer, rounding away from zero in halfway cases
(function) [edit]