Q40155: QB.EXE 4.50 Bad Alert Box if User TYPE "Element Not Defined"

Article: Q40155
Product(s): See article
Version(s): 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.50 SR# S890104-76 ptm234 | mspl13_basic
Last Modified: 8-MAR-1989

In QuickBASIC Version 4.50, if you attempt to run a program that
contains erroneous use of user-defined typed variables (specifically,
an "element not defined" error), QuickBASIC may bring up an alert box
that contains irrelevant information, and possibly garbage.

This problem occurs only in Microsoft QuickBASIC Version 4.50 for
MS-DOS. Microsoft is researching this problem and will post new
information as it becomes available.

This problem is not an issue if you always make sure to define all
elements of a user-defined TYPE before using them.

Consider the following program:

TYPE Test
  x AS INTEGER
  y AS DOUBLE
END TYPE
DIM Var AS Test
PRINT Var

To reproduce the problem, do the following:

1. Run this program as is. You should get a "Type mismatch" error
   message on the PRINT statement.

2. Change the PRINT statement line to print out an element of Var that
   does not exist (for example, PRINT Var.z).

Attempting to run the modified version of the program will produce an
alert box that contains completely random, irrelevant information,
often incomplete sentences, sometimes single words or characters, and,
occasionally, incomprehensible garbage.

If the program is run again without changing it, the same information
will appear in the alert box. However, if the PRINT statement is
changed again (i.e., to another element that does not exist), a new
alert box is produced, with different, meaningless information. If
this is repeated several times (making a change, running the program,
making a change, running the program, etc., about 30 times), the alert
box itself may be garbled or incomplete and the machine eventually
will hang.

However, if a change is made to the DIM statement line (even a
noncritical edit, such as inserting a line before the DIM statement),
you will get the correct "Element not defined" error when you run the
program. The problem will not recur from this point on, until you
change the PRINT statement back to just PRINT Var, and run to get the
"Type Mismatch" error message.

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