std::chrono::round(std::chrono::time_point)
来自cppreference.com
< cpp | chrono | time point
定义于头文件 <chrono>
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template <class ToDuration, class Clock, class Duration> constexpr std::chrono::time_point<Clock, ToDuration> |
(C++17 起) | |
返回能以 ToDuration
表示的最接近 tp
的时间点,中点情况下向偶数舍入。
函数不参与重载决议,除非 ToDuration
是 std::chrono::duration 的特化且 std::chrono::treat_as_floating_point_v<typename ToDuration::rep> 为 false 。
参数
tp | - | 要舍入到最近值的时间点 |
返回值
舍入到使用 ToDuration
类型时长的最近时间点的 tp
,中点情况下向偶数舍入。
可能的实现
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>{ std::chrono::round<To>(tp.time_since_epoch())}; } |
示例
运行此代码
#include <iostream> #include <chrono> #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> time_point_ms(value_ms); std::cout << 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"; } }
输出:
Time point Cast Floor Round Ceil (ms) (s) (s) (s) (s) 5432 5 5 5 6 5678 5 5 6 6
参阅
(C++11) |
转换时间点为同一时钟上拥有不同时长的另一时间点 (函数模板) |
转换 time_point 到另一个,向上取整 (函数模板) | |
转换 time_point 到另一个,向下取整 (函数模板) | |
(C++17) |
转换时长到另一个时长,就近取整,偶数优先 (函数模板) |
(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11) |
最接近整数,中间情况下向远离零舍入 (函数) |