Validating Select-options in SAP ABAP

Generally , while validating select-options we write the code as below.

*It is only partially correct , refer the codes below
select matnr from mara into lv_mara
                             where matnr in so_matnr.
if sy-subrc is not initial.
   "error message
endif.

but above code , is wrong . Now suppose the user enters two material number , 0000000002 and
0000000045 where the 2nd one does not exist in the system .But sy-subrc will become 0 , and the error message will not be executed .
So , we have to consider the following codes that will help !!!

REPORT  ztestr_14.

TABLES : mara.

SELECT-OPTIONS : so_matnr FOR mara-matnr.

TYPES : BEGIN OF ty_matnr,
          matnr TYPE matnr,
        END OF   ty_matnr.

DATA : li_matnr TYPE STANDARD TABLE OF ty_matnr.
FIELD-SYMBOLS : <fls_matnr> TYPE ty_matnr.

IF so_matnr IS NOT INITIAL.

  SELECT matnr FROM mara
               INTO TABLE li_matnr
               WHERE matnr IN so_matnr.

  IF sy-subrc IS INITIAL.

    SORT li_matnr ASCENDING BY matnr.

    LOOP AT so_matnr.

      READ TABLE li_matnr ASSIGNING <fls_matnr>
                          WITH KEY  matnr = so_matnr-low
                          BINARY SEARCH.

      IF sy-subrc IS NOT INITIAL.

        PERFORM error_handling USING text-e01 so_matnr-low.

      ENDIF.

    ENDLOOP.

    IF so_matnr-high IS NOT INITIAL.

      READ TABLE li_matnr ASSIGNING <fls_matnr>
                          WITH KEY  matnr = so_matnr-high
                          BINARY SEARCH.

      IF sy-subrc IS NOT INITIAL.

        PERFORM error_handling USING text-e01 so_matnr-high.

      ENDIF.

    ENDIF.

  ELSE.

     PERFORM error_handling USING text-e01 so_matnr-low.

  ENDIF.

ENDIF.

form ERROR_HANDLING  using    p_text_e01 TYPE string
                              value type any.

       DATA : lv_message TYPE string.
       CONSTANTS : lc_plach1 TYPE char2 VALUE '&1'.
        CLEAR : lv_message.
        lv_message = p_text_e01." where text-e01 = Material number &1 does not exist
        REPLACE lc_plach1 WITH value
        INTO lv_message.
        MESSAGE e000(zh) WITH lv_message.

endform.                    " ERROR_HANDLING