// Read an input file of Roman Numerals and do it all
static void do_it_all(
   std::string_view fname       //  in: file name containing a list of Roman Numerals
)
{
   try {
   #if 1
      // Load entire file to memory through memory mapping.
      using file_loader_type = fast_io::native_file_loader;
      file_loader_type loader(fname, fast_io::open_mode::in | fast_io::open_mode::follow);
      // Loop through contiguous container of the file.
      for (char const *first{loader.data()}, *last{loader.data()+loader.size()}; first!=last; ) {
         auto start_ptr{first}; first = fast_io::find_lf(first, last); auto end_ptr{first};
         if (start_ptr == end_ptr) continue;
         int dec = roman_to_dec(std::string_view(start_ptr, end_ptr - start_ptr));
         fast_io::io::println(dec);
         ++first;
      }
   #else
      fast_io::filebuf_file fbf(fname, fast_io::open_mode::in | fast_io::open_mode::follow);
      for (std::string line; fast_io::io::scan<true>(fbf, fast_io::mnp::line_get(line)); ) {
         fast_io::io::println(roman_to_dec(line));
      }
   #endif
   }
   catch (fast_io::error e) {
      fast_io::io::perrln("Error opening '", fname, "' : ", e);
   };
}