In QB.EXE 4.5, Watchpoint Won't Break on Function Return Value (80848)




This article was previously published under Q80848

SYMPTOMS

In QB.EXE, setting a watchpoint to stop on a variable whose value is assigned from the return value of a function will not break, even if the Watch window shows that the expression evaluates to TRUE.

STATUS

Microsoft has confirmed this to be a bug in the QB.EXE environment in Microsoft QuickBasic version 4.5 for MS-DOS. This problem was corrected in QBX.EXE in Microsoft Basic Professional Development System (PDS) version 7.1 for MS-DOS (fixlist7.10).

MORE INFORMATION

Setting a watchpoint creates a break in your program when certain conditions are met. For example, in your program you may want a For Loop that executes 100 times. If you want the program to stop after the loop had executed 50 times, you could set a watchpoint with the expression X=50, where X is the loop counter.

However, when you try to set a watchpoint on a variable that is set from the return value of a user defined function, when the Watch window evaluates the expression to TRUE, the program will not break.

WORKAROUND

To work around this problem, assign the results of the function to a temporary value and then assign the temporary value to x%. This will allow you to stop execution when the expression becomes TRUE. 
   FUNCTION num%
     temp% = 5
     x% = temp%
   END FUNCTION

Steps to Reproduce Problem

  1. In the QuickBasic environment, enter the following program. 
         DECLARE FUNCTION num% ()

     WHILE INKEY$ = ""
       x% = num%
     WEND

     FUNCTION num%
       num% = 5
     END FUNCTION
  2. From the Debug menu, choose Watchpoint, and add a watchpoint. At the prompt to enter the expression, type x%=5.
  3. From the Run menu, choose Start.
  4. Press any key to end the program.
In this example, notice that after the program terminates, the Watch window reads TRUE signifying that the expression was TRUE and the program should have stopped. To demonstrate the proper functionality of this operation, change the "x% = num%" in the Basic source code to be x%=5.
Modification Type: Minor Last Reviewed: 1/9/2003
Keywords: KB80848
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