table overflow when using PERFORM VARYING

September 26, 2023

I’m doing a simple PERFORM VARYING WS-IND FROM 1 BY 1

Bellow is my code:

       PERFORM VARYING WS-INDICE FROM 1 BY 1
       UNTIL WS-INDICE > 9
       OR TEST-OBJEC(WS-INDICE) = SPACES
           MOVE TEST-OBJEC(WS-INDICE) TO WS-VAL-OBJEC(WS-INDICE)
           MOVE TEST-DATE(WS-INDICE)  TO WS-DAT-OBJEC(WS-INDICE)
       END-PERFORM

Index was declared like this:

01  WS-INDICE PIC 9(01).

Bellow the declaration of my array

          10        TEST-GROUP
                           OCCURS 009.
           15       TEST-OBJEC  PICTURE X(01).
           15       TEST-DATE   PICTURE X(8).
          10        FILLER PICTURE X(56).

My problem that the WS-INDICE arrive until 9 and restart from 0.

>Solution :

Problem description

the WS-INDICE arrive until 9 and restart from 0

Code

VARYING WS-INDICE FROM 1 BY 1
        UNTIL WS-INDICE > 9

Problem reason

A compiler that both does not warn about conditions that may never be true and additional also overflows (the COBOL standard says "raise exception and don’t change value").

… because of the definition WS-INDICE PIC 9(01).

This variable cannot hold more than one digit should never be greater than 9 (leaving out the possibility that someone moves x'99' to that, inserting invalid data).

Adjust the definition to use a PIC 99 and everything is fine.
And possibly consider to use constants instead:

          10        TEST-GROUP
-                          OCCURS 009.
+                          OCCURS WS-INDICE-MAX.

        PERFORM VARYING WS-INDICE FROM 1 BY 1
-       UNTIL WS-INDICE > 9
+       UNTIL WS-INDICE > WS-INDICE-MAX

For this to work you’d need support for either a common PC extension "level 78 constants" or a compiler that supports "COBOL 2002 constants":

       78  WS-INDICE-MAX    VALUE 9.
       01  integer-constant CONSTANT AS 9.

… and possibly consider to use another compiler for better warnings (you don’t need to use that otherwise), for example with GnuCOBOL 3+ and cobc -W -frelax-syntax-checks -fsyntax-only: