std::chrono::duration

std::chrono::duration是一个C++标准库中的时间库，用于表示时间段。它是一个模板类，可以用来表示不同单位的时间长度。这个类包含了几种不同的表示方式，例如以毫秒、微秒、纳秒等为单位的时间长度。

相关问题

get std::chrono::duration from std::chrono::point_time

Unfortunately, there is no direct way to obtain a `std::chrono::duration` from a `std::chrono::point_time`. However, you can calculate the duration between two `std::chrono::point_time` instances using the `std::chrono::duration_cast` function. Here's an example:

#include <chrono>

int main() {
    using namespace std::chrono;

    // Create two point_time instances
    auto start = system_clock::now();
    auto end = system_clock::now() + seconds(30);

    // Calculate the duration between the two point_time instances
    auto duration = duration_cast<seconds>(end - start);

    // Print the duration in seconds
    std::cout << duration.count() << " seconds\n";

    return 0;
}

In this example, we create two `system_clock::now()` instances to represent the start and end times. We then calculate the duration between them using the `duration_cast` function, which converts the difference between the two `point_time` instances into a `duration` of seconds. Finally, we print the duration in seconds using the `count` function.

std::chrono::time_pointstd::chrono::steady_clock end = std::chrono::steady_clock::now(); auto elapsed = std::chrono::duration_cast<std::chrono::seconds>(end - start); auto替换成真正的类型

在这段代码中，`auto`被用于推断`elapsed`变量的类型。如果您想要替换`auto`为真正的类型，可以将其替换为`std::chrono::seconds`，即：

std::chrono::time_point<std::chrono::steady_clock> end = std::chrono::steady_clock::now();
std::chrono::seconds elapsed = std::chrono::duration_cast<std::chrono::seconds>(end - start);

这样，`elapsed`变量的类型就被明确指定为了`std::chrono::seconds`。需要注意的是，如果您想要以其他时间单位（如毫秒、微秒等）来表示时间间隔，需要将`std::chrono::seconds`替换为相应的类型，如`std::chrono::milliseconds`、`std::chrono::microseconds`等。