# std::chrono::treat_as_floating_point

< cpp‎ | chrono

定义于头文件 `<chrono>` |  |
template <class Rep> struct treat_as_floating_point : std::is_floating_point<Rep> {}; |  | (C++11 起)

`std::chrono::treat_as_floating_point` 特性帮助确定时期是否能转换成拥有另一种不同计次周期的时期。

二个时期间的隐式转换通常依赖于时期的计次周期。然而若 std::chrono::treat_as_floating_point<Rep>::value == true 则可发生隐式转换，不管计次周期如何。

### 辅助变量模板

template< class Rep > inline constexpr bool treat_as_floating_point_v = treat_as_floating_point<Rep>::value; |  | (C++17 起)

### 特化

可对程序定义类型特化 `std::chrono::treat_as_floating_point` 。

### 示例

    #include <iostream>
    #include <chrono>
    #include <thread>

    void timed_piece_of_code()
    {
        std::chrono::milliseconds simulated_work(2);
        std::this_thread::sleep_for(simulated_work);
    }

    int main()
    {
        auto start = std::chrono::high_resolution_clock::now();

        std::cout << "Running some timed piece of code..." << '\n';
        timed_piece_of_code();

        auto stop = std::chrono::high_resolution_clock::now();

        // 浮点毫秒类型
        using FpMilliseconds =
            std::chrono::duration<float, std::chrono::milliseconds::period>;

        static_assert(std::chrono::treat_as_floating_point<FpMilliseconds::rep>::value,
                      "Rep required to be floating point");

        // 注意此处不允许隐式转换
        auto i_ms = std::chrono::duration_cast<std::chrono::milliseconds>(stop - start);

        // 注意此处允许隐式转换
        auto f_ms = FpMilliseconds(stop - start);

        std::cout << "Time in milliseconds, using default rep: "
                  << i_ms.count() << '\n';

        std::cout << "Time in milliseconds, using floating point rep: "
                  << f_ms.count() << '\n';

    }

可能的输出：

    Running some timed piece of code...
    Timing stats:
      Time in milliseconds, using default rep: 2
      Time in milliseconds, using floating point rep: 2.57307

### 参阅