PRB: MSMQQueue Object IsOpen Property Returns an Integer

• Microsoft Message Queue Server versions 1.0, 2.0

SYMPTOMS

The IsOpen property of a Microsoft Message Queue (MSMQ) MSMQQueue object returns an Integer result rather than a Boolean. IsOpen property returns a 1 if the queue is open and a 0 if it is not. This can cause logic errors in a Visual Basic (VB) program if the property is used in the expression portion of an If, While, or similar conditional statement.

When a numeric value is used in a condition statement in VB, 0 is evaluated as false and all non-zero values are evaluated as true. The Not operator in VB inverts the bits of a value when used on a numeric value. The expression "Not 1" produces the result "-2" which is considered a "true" value in a VB condition statement.

Since VB evaluates both "1" and "Not 1" as true statements, if a queue is open both "queue.IsOpen" and "Not queue.IsOpen" will evaluate true. In the following example code, if the queue is open both message boxes appear:

If queue.IsOpen Then
   MsgBox "The queue is open"
End If

If Not queue.IsOpen Then
   MsgBox "The queue is closed"
End If 

RESOLUTION

There are two possible workarounds for the problem:

1. Explicitly test the value of the IsOpen property against 0 and 1. A value of 1 indicates that the queue is open, a value of 0 indicates that the queue is not open. An example of this test is shown in the following code:
   

   
   If MSMQQueueObject.IsOpen = 1 Then
      MsgBox "The queue is open."
   End If
   
   If MSMQQueueObject.IsOpen = 0 Then
      MsgBox "The queue is closed"
   End If 




2. Avoid "negative" tests that use the Not operator with the IsOpen property.

STATUS

It is safe to test explicitly for the 1 and 0 values. These values will not be changed in any future version of MSMQ and will remain consistent. Future versions of the MSMQ ActiveX components may add a property that may be evaluated as a true Boolean type for testing this characteristic.

MORE INFORMATION

The MSDN Online help describes the return values for the IsOpen property as follows:

MSMQQueue.IsOpen

Return Values
1 
   The queue is open. 
0 
   The queue is not open.  

REFERENCES

MSDN Online help for the MSMQQueue object type.
Visual Basic Programmers Guide

Q246218 MSMQMessage Object IsAuthenticated Property Returns an Integer

Q246222 MSMQQueueInfo Object IsTransactional Property Returns An Integer

Q246225 MSMQQueueInfo Object IsWorldReadable Property Returns and Integer

Q246458 MSMQMessage Object IsFirstInTransaction Property Returns An Integer

Q246460 MSMQMessage Object IsLastInTransaction Property Returns An Integer

Additional query words: MSMQ MSMQQueue IsOpen

Keywords : kbMSMQ kbMSMQ100 kbMSMQ100bug kbDSupport
Version : winnt:1.0,2.0
Platform : winnt
Issue type : kbprb