Q34283: BC Hangs on a POKE with a FUNCTION Passed a Dynamic Array

Article: Q34283
Product(s): See article
Version(s): 4.00 4.00b
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00 buglist4.00b fixlist4.50 B_BasicCom | mspl13_basic
Last Modified: 11-DEC-1989

BC.EXE hangs at compile time when compiling the program below. This
program uses a POKE statement that directly invokes a FUNCTION
procedure that is passed a dynamic-array element as an argument.

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

The following are several workarounds for this problem:

1. Make the array STATIC instead of DYNAMIC.

2. Use a temporary variable to pass the array element to the FUNCTION
   procedure.

3. Use a temporary variable to receive the value returned from the
   FUNCTION and POKE that temporary variable.

Note that Page 201 of the "Microsoft QuickBASIC 4.0: BASIC Language
Reference" manual gives the following related information:

   "Because BASIC may rearrange arithmetic expressions for
    greater efficiency, avoid using FUNCTION procedures that
    change program variables in arithmetic expressions."

The following code example demonstrates the problem:

REM This program demonstrates the problem at compile-time in BC.EXE
DEFINT A-Z
DECLARE FUNCTION charOff (row)
REM $DYNAMIC
DIM SHARED a(4)  AS INTEGER
' Poke a value returned by a function that is passed a dynamic
' array element:
POKE charOff(a(1)), 210
END

FUNCTION charOff (row)
END FUNCTION

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