[open-cobol-list] EVALUATE NULL issue

[Tim Nixon]

EVALUATE NULL issue

 

The following code works:

     WORKING-STORAGE SECTION.

       01 NEWVAR POINTER.

     PROCEDURE DIVISION.

         MOVE NULL TO NEWVAR.

        EVALUATE NEWVAR

            WHEN NULL

                 DISPLAY "NEWVAR IS NULL"

            WHEN OTHER

                 DISPLAY "NEWVAR is NOT NULL"

         END-EVALUATE.

=====================================

But with the same beginning code this does not compile

          EVALUATE NULL

               WHEN NEWVAR

                     DISPLAY "NEWVAR IS NULL"

               WHEN OTHER

                     DISPLAY "NEWVAR is NOT NULL"

          END-EVALUATE.

-----------------------------------------------

The difference is that EVALUATE <var> WHEN NULL generates correct c-code, but EVALUATE NULL WHEN <var> does not.

for the working case the generated c code line is this:

   if((((*(unsigned char**)(b_6))-0) == 0))

for the non working case it's

   if(((0-(*(unsigned char**)(b_6))) == 0))

 

the real issue is that in c its allowable to subtract a value from a pointer, but not a pointer from a value. In other words (ADDRESS - number)  is OK, but (number - ADDRESS)  is not.

------------------------------------------------

 

FIX: in codegen.c, output_integer() function  added test case for cb_null and wrapped output value of NULL in a typecast... rather than outputting just a "0".

Listing: (NOTE: line numbers may not be exact)

 

    524 static void

    525 output_integer (cb_tree x)

    526 {

    527   switch (CB_TREE_TAG (x))

    528     {

    529     case CB_TAG_CONST:

    530       if (x == cb_zero)

    531         output ("0");

    532       else

    533 /*********FIX*************/

    534        if(x == cb_null){

    535               output (" ((unsigned char *)NULL) ");

    536         }else

    537 /*********END FIX*************/

    538        output ("%s", CB_CONST (x)->val);

    539       break;

    540     case CB_TAG_INTEGER:

 

Tim Nixon