c++ - 在 C++ 中，时钟稳定状态是否依赖于编译器？

Question

我用下面的代码，输出3个时钟的稳定状态

#include <chrono>
#include <iostream>
#include <iomanip>

template <typename C>
void printClockData ()
{
    using namespace std;

    cout << "- precision: ";
    // if time unit is less or equal one millisecond
    typedef typename C::period P;// type of time unit
    if (ratio_less_equal<P,milli>::value) {
        // convert to and print as milliseconds
        typedef typename ratio_multiply<P,kilo>::type TT;
        cout << fixed << double(TT::num)/TT::den
             << " milliseconds" << endl;
    }
    else {
        // print as seconds
        cout << fixed << double(P::num)/P::den << " seconds" << endl;
    }
    cout << "- is_steady: " << boolalpha << C::is_steady << endl;
}

int main()
{
    std::cout << "system_clock: " << std::endl;
    printClockData<std::chrono::system_clock>();
    std::cout << "\nhigh_resolution_clock: " << std::endl;
    printClockData<std::chrono::high_resolution_clock>();
    std::cout << "\nsteady_clock: " << std::endl;
    printClockData<std::chrono::steady_clock>();
}

用g++编译，输出

使用 intel icl 输出编译

为什么不同？

Answer 1

是的，对于 high_resolution_clock。正如 C++ 标准所说:

20.12.7.3 Class high_resolution_clock

Objects of class high_resolution_clock represent clocks with the shortest tick period. high_resolution_clock may be a synonym for system_clock or steady_clock.

例如Visual C++ 2015是否已将其类型定义为 steady_clock，Intel 可能也是。

对于 steady_clock，标准明确将 is_steady 设置为 true。