How to convert errno to exception using

You are on the right track, just pass the error code and a std::generic_category object to the std::system_error constructor and it should work.

Example:

#include <assert.h>
#include <errno.h>
#include <iostream>
#include <system_error>

int main()
{
    try
    {
        throw std::system_error(EFAULT, std::generic_category());
    }
    catch (std::system_error& error)
    {
        std::cout << "Error: " << error.code() << " - " << error.what() << '\n';
        assert(error.code() == std::errc::bad_address);
    }
}

Output from the above program on my system is

Error: generic:14 - Bad address