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

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如果你有 std::chrono::time_point 如

timepoint_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微秒

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

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

duration_cast_microseconds.cpp
std::chrono::duration_cast<std::chrono::microseconds>(timepoint.time_since_epoch()).count()

完整示例：

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

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

例如，这会打印：

chrono_microseconds_example_output.txt
Microseconds since epoch: 1690755479946000

这是一个将 std::chrono::time_point 转换为微秒的简单代码片段：

timepoint_to_us.cpp
#include <chrono>
#include <cstdint>

int64_t to_microseconds_since_epoch(std::chrono::system_clock::time_point tp) {
    return std::chrono::duration_cast<std::chrono::microseconds>(tp.time_since_epoch()).count();
}

使用示例：

timepoint_usage.cpp
auto now = std::chrono::system_clock::now();
int64_t us = to_microseconds_since_epoch(now);
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