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Q57356: "Overflow" Accessing > 32K Array Inside User-Defined TYPE

Article: Q57356
Product(s): See article
Version(s): 7.00   | 7.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | SR# S891113-17 buglist7.00 | mspl13_basic
Last Modified: 14-JAN-1990

When a program is compiled with the /D switch, the length of arrays
inside user-defined TYPEs is limited to 32,768 bytes. The compiler
will not generate an error if a larger array is declared inside a
user-defined type, but accessing any element that is offset more than
32,768 bytes into the array will cause an "Overflow" error.

Microsoft has confirmed this to be a problem in Microsoft BASIC
Professional Development System (PDS) Version 7.00 for MS-DOS and MS
OS/2. We are researching this problem and will report new information
here as it becomes available.

This limitation applies only to arrays inside user-defined TYPEs, a
new feature that was introduced in BASIC PDS 7.00 for MS-DOS and MS
OS/2.

The following two examples illustrate when the "Overflow" error occurs
and when it doesn't.

Example 1
---------

When compiled with the BC /D switch, this program generates an
"Overflow" error. This is because element 16,385 of the INTEGER array
inside of the user-defined TYPE is being accessed. 16,385 * 2 (2 bytes
per INTEGER) is greater than 32,768, so that element is out of bounds.

TYPE aType
   anArray (1 TO 16385) AS INTEGER  'The compiler will not
                                    'flag this as an error -
END TYPE                            '(16385*2) > 32768
DIM aVariable as aType

FOR i = 1 TO 16385
   aVariable.anArray(i) = 1   'When i = 16385 the "Overflow"
NEXT i                        'error will be generated.

Example 2
---------

The following program does not generate an "Overflow" error. This is
because the highest element of the INTEGER array inside the
user-defined type being accessed is 16,384. 16,384 * 2 (2 bytes per
INTEGER) is not greater than 32,768, so the element is not out of
bounds.

TYPE aType
   anArray (1 TO 16385) AS INTEGER  'The compiler will not
                                    'flag this as an error -
END TYPE                            '(16385 * 2) > 32768
DIM aVariable as aType

FOR i = 1 TO 16384
   aVariable.anArray(i) = 1   'No "Overflow" error -
NEXT i                        '16384 * 2 <= 32768.

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