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如何将 std::chrono::time_point 转换为自纪元以来的秒

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如果你有 std::chrono::time_point 如

example.cpp
std::chrono::time_point<std::chrono::system_clock> timepoint = std::chrono::system_clock::now();

你可以通过首先使用将其转换为 chrono::duration 来转换为自纪元以来的秒

example.cpp
timepoint.time_since_epoch(); // Returns a duration

然后使用 std::chrono::duration_cast<std::chrono::seconds>(...).count() 将其转换为自纪元以来的 seconds 并获取纪元和时间点之间的间隔数（= 秒）。

example.cpp
std::chrono::duration_cast<std::chrono::seconds>(timepoint.time_since_epoch()).count()

完整示例：

main.cpp
#include <chrono>
#include <iostream>

int main()
{
    auto timepoint = std::chrono::system_clock::now();
    std::cout << "Seconds since epoch: " <<
        std::chrono::duration_cast<std::chrono::seconds>(timepoint.time_since_epoch()).count() << std::endl;
}

例如，这会打印：

output.txt
Seconds since epoch: 1690755234
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