"Subscript Out of Range" Using ERASEd Array in a SUB (49210)


The information in this article applies to:

  • Microsoft QuickBASIC 4.0, when used with:
    • the operating system: MS-DOS
  • Microsoft QuickBASIC 4.0b, when used with:
    • the operating system: MS-DOS
  • Microsoft QuickBASIC 4.5, when used with:
    • the operating system: MS-DOS
This article was previously published under Q49210

SYMPTOMS

In the QuickBasic editor, the ERASE statement frees the memory for an array DIMensioned in a non-STATIC SUBprogram, even if the $STATIC metacommand is used. Because the memory for the array has been deallocated, a "Subscript out of range" error results the next time an attempt is made to access the array beyond element 10.

STATUS

Microsoft has confirmed this to be a bug in QB.EXE in QuickBasic Versions 4.00, 4.00b, and 4.50 for MS-DOS. This problem was corrected in the QBX.EXE environment of Microsoft Basic Professional Development System (PDS) Version 7.00 for MS-DOS and MS OS/2 (fixlist7.00).

MORE INFORMATION

This behavior does not occur in a compiled .EXE program. In an .EXE program, a $STATIC array DIMensioned in a SUBprogram that is ERASEd remains allocated, and the ERASE initializes all elements to their default value (0 or "").

WORKAROUND

The best workaround is to reinitialize the array without using the ERASE statement. Alternatively, you can DIM the array at the main module level and share it with the SUBprogram with the SHARED statement. Both methods ensure that memory for the array is not freed by ERASE.

Another possible workaround for this problem is to make the SUBprogram STATIC by placing the STATIC clause on the SUB or FUNCTION statement. This method should be used with caution. Normally, Basic allocates memory for variables in SUBprograms on the stack, and the memory is released when the SUB is exited. Making the SUBprogram STATIC causes all variables in the SUBprogram to be permanently allocated, which permanently reduces the space available for other variables and strings. A STATIC SUBprogram also has to initialize its own variables, and a STATIC SUBprogram cannot be recursive.

Code Example

The following program demonstrates the "Subscript out of range" error caused by erasing an array that was DIMensioned in a non-STATIC SUBprogram in the QuickBasic QB.EXE environment: 
DECLARE SUB Test ()
CALL Test
END

SUB Test
  DIM A$(100)
  ERASE A$
  PRINT A$(80)           ' "Subscript Out of Range" occurs.
END SUB

Workaround 1

Initialize the array without ERASE, as follows: 
DECLARE SUB Test ()
 
CALL Test
END
 
SUB Test
 
  DIM A$(100)
  FOR I = 1 TO 100
 
      A$(I) = ""
 
  NEXT
  PRINT A$(80)
 
END SUB

Workaround 2

DIM the array in the main level of the module and SHARE it in the SUB, as follows: 
DECLARE SUB Test ()
 
DIM A$(100)
CALL Test
END
 
 
SUB Test
 
  SHARED A$()
  ERASE A$
  PRINT A$(80)
 
END SUB

Workaround 3

Use a STATIC SUBprogram, as follows: 
DECLARE SUB Test ()
 
CALL Test
END
 
SUB Test STATIC          'Added STATIC
 
  DIM A$(100)
  ERASE A$
  PRINT A$(80)
 
END SUB
Modification Type:MinorLast Reviewed:1/8/2003
Keywords:KB49210
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