Q33687: Temporary Memory in SUBprogram Is Not Deallocated after CALL

Article: Q33687
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00 buglist4.00b buglist4.50 B_BasicCom | mspl13_basic
Last Modified: 13-DEC-1989

In EXE form, the following program uses 8K of memory, not 4K as it
should. The program does not seem to deallocate the temporary memory
after calling the dynamic subprogram. The program works correctly
inside the QB.EXE editor. To duplicate the problem, the array needs to
be dimensioned after the COMMON block (to make it dynamic) and 4K of
data needs to be assigned inside the subprogram, as shown.

Microsoft has confirmed this to be a problem in QuickBASIC Versions
4.00, 4.00b, and 4.50, and in Microsoft BASIC Compiler Versions 6.00,
6.00b for MS-DOS and MS OS/2 (buglist6.00, buglist6.00b). This problem
was corrected in Microsoft BASIC PDS Version 7.00 (fixlist7.00).

To work around the problem, declare the array as static instead of as
dynamic. You can make the array static by dimensioning it before the
COMMON statement.

Note: This problem does not occur in QuickBASIC Version 3.00.

The following code example demonstrates this problem:

   DECLARE SUB SaveWindow (WindowBuffer$)
   COMMON tmp$()
   DIM tmp$(10)
   PRINT FRE(""), FRE(-1)
   CALL SaveWindow(tmp$(5))
   PRINT FRE(""), FRE(-1),
   END
   SUB SaveWindow (WindowBuffer$)
     size% = 4000
     WindowBuffer$ = STRING$(size%, CHR$(0))
   END SUB

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