Replace macro with `std::to_string`

   set coeffs for one or more type pairs

------------------------------------------------------------------------- */

#ifdef SNUM

#undef SNUM

#endif

#define SNUM(x)                                                \

  static_cast<std::ostringstream const &>(std::ostringstream() \

                                          << std::dec << x).str()

void PairKIM::coeff(int narg, char **arg)

{

  // This is called when "pair_coeff ..." is read from input

          if (nubound < 1 || nubound > extent ||

              nlbound < 1 || nlbound > nubound) {

            std::string msg("Illegal index_range '");

            msg += SNUM(nlbound) + "-" + SNUM(nubound);

            msg += std::to_string(nlbound) + "-" + std::to_string(nubound);

            msg += "' for '";

            msg += paramname;

            msg += "' parameter with extent of '";

            msg += SNUM(extent);

            msg += std::to_string(extent);

            msg += "' .";

            error->all(FLERR, msg);

          }

          str >> nlbound;

          if (nlbound < 1 || nlbound > extent) {

            std::string msg("Illegal index '");

            msg += SNUM(nlbound) + "' for '";

            msg += std::to_string(nlbound) + "' for '";

            msg += paramname;

            msg += "' parameter with extent of '";

            msg += SNUM(extent);

            msg += std::to_string(extent);

            msg += "' .";

            error->all(FLERR, msg);

          }

        std::string msg =

        "Wrong number of variable values for pair coefficients.\n";

        msg += "'";

        msg += SNUM(nubound - nlbound + 1);

        msg += std::to_string(nubound - nlbound + 1);

        msg += "' values are requested for '";

        msg += paramname;

        msg += "' parameter.";

  }

}

#undef SNUM

/* ----------------------------------------------------------------------

   init specific to this pair style

------------------------------------------------------------------------- */