Microsoft KB Archive/245753

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Article ID: 245753

Article Last Modified on 2/22/2007


  • Microsoft Message Queue Server 1.0
  • Microsoft Message Queuing 2.0

This article was previously published under Q245753


The IsOpen property of a Microsoft Message Queuing MSMQQueue object returns an Integer result rather than a Boolean.

Note Microsoft Message Queuing is also known as MSMQ.

The 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


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.


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


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


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


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

246218 MSMQMessage Object IsAuthenticated Property Returns an Integer

246222 MSMQQueueInfo Object IsTransactional Property Returns An Integer

246225 MSMQQueueInfo Object IsWorldReadable Property Returns and Integer

246458 MSMQMessage Object IsFirstInTransaction Property Returns An Integer

246460 MSMQMessage Object IsLastInTransaction Property Returns An Integer

Additional query words: MSMQ MSMQQueue IsOpen

Keywords: kbbug kbprb KB245753