errno

#include <cerrno>
#include <clocale>
#include <cmath>
#include <cstring>
#include <iostream>

int main()
{
    const double not_a_number = std::log(-1.0);
    std::cout << not_a_number << '\n';
    
    if (errno == EDOM)
    {
        std::cout << " log(-1): " << std::strerror(errno) << '\n';
        std::setlocale(LC_MESSAGES, "de_DE.utf8");
        std::cout << ",  , " << std::strerror(errno) << '\n';
    }
}