std::chrono::treat_as_floating_point

 

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std::chrono::duration

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辅助类
common_type treat_as_floating_point      duration_values	formatter<std::chrono::duration> (C++20) hash<std::chrono::duration> (C++26)

 

在标头 <chrono> 定义
template< class Rep > struct treat_as_floating_point : std::is_floating_point<Rep> {};		(C++11 起)

std::chrono::treat_as_floating_point 特征帮助确定时长是否能转换成拥有另一种不同计次周期的时长。

两个时长间的隐式转换通常依赖于时长的计次周期。然而若 std::chrono::treat_as_floating_point<Rep>::value == true 则不管计次周期如何，均可发生隐式转换。

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

可针对程序定义的类型特化 std::chrono::treat_as_floating_point。

示例

运行此代码

#include <chrono>
#include <iostream>
#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 << "运行一些耗时代码...\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 << "计时统计:\n";
 
    std::cout << "  使用默认表示的按毫秒计时间: "
              << i_ms.count() << '\n';
 
    std::cout << "  使用浮点表示的按毫秒计时间: "
              << f_ms.count() << '\n';
}

可能的输出：

运行一些耗时代码...
计时统计:
  使用默认表示的按毫秒计时间: 2
  使用浮点表示的按毫秒计时间: 2.57307