- str += _f ("unrecognized option: `%s\'",
- String (argument_index_i_
- ? String ("-" + String_convert::form_str ("%c",
- arg_value_ch_a_a_[array_index_i_][argument_index_i_]))
- : String (arg_value_ch_a_a_[array_index_i_])));
+ str += _f ("unrecognized option: `%s'",
+ string (argument_index_
+ ? string ("-" + string (1, arg_value_char_a_a_[array_index_][argument_index_]))
+ : string (arg_value_char_a_a_[array_index_])));