std::chrono::floor(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 time_point<Clock, ToDuration> floor(const time_point<Clock, Duration>& tp); |
(C++17 起) | |
返回能以 ToDuration 表示的小于或等于 tp 的最大时间点 t 。
函数不参与重载决议，除非 ToDuration 是 std::chrono::duration 的特化。
参数
| tp | - | 要向下舍入的 time_point |
返回值
向下舍入到使用 ToDuration 类型时长的下一个时间点的 tp 。
可能的实现
template <class T> struct is_duration : std::false_type {}; template <class Rep, class Period> struct is_duration< std::chrono::duration<Rep, Period>> : std::true_type {}; template <class To, class Clock, class FromDuration, class = std::enable_if_t<is_duration<To>{}>> constexpr std::chrono::time_point<Clock, To> floor(const std::chrono::time_point<Clock, FromDuration>& tp) { return std::chrono::time_point<Clock, To>{ std::chrono::floor<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
| 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，就近取整，偶数优先 (函数模板) | |
| (C++17) |
以向下取整的方式，将一个时长转换为另一个时长 (函数模板) |
| (C++11)(C++11) |
不大于给定值的最接近整数 (函数) |
