std::numeric_limits<T>::signaling_NaN

Демонстрирует использование сигнального NaN для возникновения исключения с плавающей точкой:

#include <cfenv>
#include <iostream>
#include <limits>

#pragma STDC FENV_ACCESS ON

void show_fe_exceptions()
{
    int n = std::fetestexcept(FE_ALL_EXCEPT);
    
    if (n & FE_INVALID)
        std::cout << "FE_INVALID is raised\n";
    else if (n == 0)
        std::cout << "no exceptions are raised\n";
    
    std::feclearexcept(FE_ALL_EXCEPT);
}

int main()
{
    double snan = std::numeric_limits<double>::signaling_NaN();
    std::cout << "After sNaN was obtained, ";
    show_fe_exceptions();
    
    double qnan = snan * 2.0;
    std::cout << "After sNaN was multiplied by 2, ";
    show_fe_exceptions();
    
    qnan *= 2.0;
    std::cout << "After the quieted NaN was multiplied by 2, ";
    show_fe_exceptions();
    
    std::cout << "The result is " << qnan << '\n';
}

Вывод:

After sNaN was obtained, no exceptions are raised
After sNaN was multiplied by 2, FE_INVALID is raised
After the quieted NaN was multiplied by 2, no exceptions are raised
The result is nan