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    std::chrono::time_point<Clock,Duration>::time_since_epoch

    来自 zh.cppreference.net
     
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    日期和时间库
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    chrono 输入/输出
    (C++20)

     
    std::chrono::time_point
     
    duration time_since_epoch() const;
    		（从 C++11 开始）
    （从 C++14 起 constexpr）

    返回一个 std::chrono::duration 表示 *this 与 clock 的纪元之间的时间量。

    返回值

    该 time_point 与 clock 纪元之间的时间量。

    示例

    运行此代码
    #include <chrono>
#include <ctime>
#include <iostream>

int main()
{
    const auto p0 = std::chrono::time_point<std::chrono::system_clock>{};
    const auto p1 = std::chrono::system_clock::now();
    const auto p2 = p1 - std::chrono::hours(24);
 
    std::time_t epoch_time = std::chrono::system_clock::to_time_t(p0);
    std::cout << "epoch: " << std::ctime(&epoch_time);
    std::time_t today_time = std::chrono::system_clock::to_time_t(p1);
    std::cout << "today: " << std::ctime(&today_time);
 
    std::cout << "hours since epoch: "
              << std::chrono::duration_cast<std::chrono::hours>(
                     p1.time_since_epoch()).count()
              << '\n';
    std::cout << "yesterday, hours since epoch: "
              << std::chrono::duration_cast<std::chrono::hours>(
                     p2.time_since_epoch()).count()
              << '\n';
}

    可能的输出： 

    epoch: Thu Jan  1 00:00:00 1970
today: Fri Jun 30 10:44:11 2017
hours since epoch: 416338
yesterday, hours since epoch: 416314