std::hash<std::chrono::time_point>

 

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日期和时间工具

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time_point (C++11)	clock_time_conversion (C++20)	clock_cast (C++20)
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duration (C++11)
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C 风格日期和时间

 

std::chrono::time_point

成员函数

time_point::time_point

time_point::time_since_epoch

time_point::operator+=time_point::operator-=

time_point::operator++time_point::operator-- (C++20)(C++20)

time_point::min

time_point::max

非成员函数

operator+operator-

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20 前)(C++20)

time_point_cast

floor (C++17)

ceil (C++17)

round (C++17)

辅助类

common_type

hash<std::chrono::time_point> (C++26)

 

在标头 <chrono> 定义
template< class Clock, class Duration > struct hash<std::chrono::time_point<Clock, Duration>>;		(C++26 起)

std::hash 对 std::chrono::time_point 的模板特化允许用户获得 std::chrono::time_point<Clock, Duration> 类型对象的散列值。此特化当且仅当 std::hash<Duration> 得到启用时才会启用。

注解

功能特性测试宏	值	标准	功能特性
__cpp_lib_chrono	202306L	(C++26)	std::chrono 值类的散列支持

示例

运行此代码

#include <chrono>
#include <cstddef>
#include <iostream>
#include <string>
#include <thread>
#include <unordered_map>
 
struct my_system_clock : std::chrono::system_clock
{
    using time_point = std::chrono::time_point<my_system_clock>;
 
    static time_point now() noexcept
    {
        return time_point{std::chrono::system_clock::now().time_since_epoch()};
    }
 
    template<class CharT, class Traits>
    friend auto operator<<(std::basic_ostream<CharT, Traits>& os, const time_point& tp)
        -> decltype(os)
    {
        return os << std::chrono::system_clock::time_point{tp.time_since_epoch()};
    }
};
 
using my_system_clock_tp = std::chrono::time_point<my_system_clock>;
 
#if __cpp_lib_chrono < 202306L
// std::hash 的自定义特化可以注入命名空间 std
template<>
struct std::hash<my_system_clock_tp>
{
    std::size_t operator()(const my_system_clock_tp& d) const noexcept
    {
        return d.time_since_epoch().count();
    }
};
#endif
 
int main()
{
    using namespace std::chrono_literals;
 
    std::unordered_map<my_system_clock_tp, std::string> log;
 
    for (int i{}; i != 4; ++i)
    {
        std::this_thread::sleep_for(100ms);
        log[my_system_clock::now()] = "事件 #" + std::to_string(i);
    }
 
    for (auto const& [time, message] : log)
        std::cout << "[" << time << "]，消息：" << message << '\n';
}

可能的输出：

[2024-03-22 10:51:02.276372448]，消息：事件 #3
[2024-03-22 10:51:02.176229944]，消息：事件 #2
[2024-03-22 10:51:02.076080700]，消息：事件 #1
[2024-03-22 10:51:01.975911017]，消息：事件 #0

参阅

hash (C++11)

散列函数对象 (类模板)