 *str_ = 0;          switch (ch_)         {         case 'd':             str_ = "[0-0]";             break;         case 'D':             str_ = "[^0-0]";             break;         case 's':             str_ = "[ \t\n\r\f\v]";             break;         case 'S':             str_ = "[^ \t\n\r\f\v]";             break;         case 'w':             str_ = "[_0-0A-Za-z]";             break;         case 'W':             str_ = "[^_0-0A-Za-z]";             break;         }          if (str_)         {             // Some systems have 