std::chrono::treat_as_floating_point

 

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std::chrono::duration

成員函式
duration::duration duration::operator= duration::count duration::zero duration::min duration::max duration::operator+duration::operator-	duration::operator++duration::operator-- duration::operator+=duration::operator-=duration::operator*=duration::operator/=duration::operator%=
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operator+operator-operator*operator/operator% operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(C++20) operator<< (C++20)	duration_cast floor (C++17) ceil (C++17) round (C++17) abs (C++17) operator""h (C++14) operator""min (C++14) operator""s (C++14) operator""ms (C++14) operator""us (C++14) operator""ns (C++14) from_stream (C++20)
輔助類
common_type treat_as_floating_point      duration_values	formatter<std::chrono::duration> (C++20) hash<std::chrono::duration> (C++26)

 

定義於標頭檔案 <chrono>
template< class Rep > struct treat_as_floating_point : std::is_floating_point<Rep> {};		(C++11 起)

std::chrono::treat_as_floating_point 特徵有助於確定一個時長（duration）是否可以轉換為具有不同刻度週期的另一個時長。

兩個時長之間的隱式轉換通常取決於時長的刻度週期。但是，如果 std::chrono::treat_as_floating_point<Rep>::value 為 true，則無論刻度週期如何，都可以發生隱式轉換。

輔助變數模板

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

特化

std::chrono::treat_as_floating_point 可以為程式定義的型別進行特化。

示例

執行此程式碼

#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 << "Running some timed piece of code...\n";
    timed_piece_of_code();
 
    auto stop = std::chrono::high_resolution_clock::now();
 
    // A floating point milliseconds type
    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");
 
    // Note that implicit conversion is not allowed here    
    auto i_ms = std::chrono::duration_cast<std::chrono::milliseconds>(stop - start);
 
    // Note that implicit conversion is allowed here
    auto f_ms = FpMilliseconds(stop - start);
 
    std::cout << "Timing stats:\n";
 
    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';
}

可能的輸出

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