7.4.13 OPT_ARG( <NAME> ) - Option Argument String

The option argument value as a pointer to string. Note that argument values that have been specified as numbers are stored as numbers or keywords. For such options, use instead the OPT_VALUE_name define. It is used thus:

if (HAVE_OPT( NAME )) {
    char* p = OPT_ARG( NAME );
    <do-things-with-opt-name-argument-string>;
}