Do you mean to do something like that : 

MCAutoStringRef t_certpath_string_tmp, t_certpath;
char *utf8str = NULL;
if (MCS_resolvepath(*t_oldcertpath_string, &t_certpath_string_tmp))
{
      /* UNCHECKED */ MCStringConvertToUTF8String(*t_certpath_string_tmp, utf8str);
      /* UNCHECKED */ MCStringCreateWithCString(utf8str, &t_certpath);
      delete utf8str;
}