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| Null pointer error GETting messages from a queue in... VBA |
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Message
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| bathouin |
 Posted: Mon Apr 02, 2007 9:34 am Post subject: Null pointer error GETting messages from a queue in... VBA |
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Newbie
Joined: 02 Apr 2007
Posts: 3
Location: Switzerland
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Hi
I'm trying to use MQ from a MS Access application. I worked long time ago with MQ under VMS, so I'm not new to the concept, but certainly to the details under Windows XP and VBA... I succeeded in connecting to a QManager, to open the default queue, and to PUT messages in that queue. However, when I try to read the messages that I have put in the queue, I invariably get an MQRC_NULL_POINTER error, and I have no idea why. Here is my very simple code:
Public Sub GETMessages()
Dim qManager As New MQQueueManager
Dim q As MQQueue
Dim qMsg As MQMessage
Dim sTemp As String
Call ConnectToQMan("", qManager)
Call OpenQueueForRead(qManager, "default", q)
sTemp = "A"
While sTemp <> ""
Call GetQueue(q, qMsg)
sTemp = qMsg.MessageData
If sTemp = "" Then Exit Sub
Debug.Print sTemp
Wend
End Sub
Public Sub OpenQueueForRead(qManager As MQQueueManager, qName As String, q As MQQueue)
Set q = qManager.AccessQueue(qName, MQOO_INPUT_SHARED + MQOO_BROWSE)
q.Open
End Sub
Public Sub GetQueue(q As MQQueue, qMsg As MQMessage)
Dim gmo As MQGetMessageOptions
Set gmo = New MQGetMessageOptions
gmo.Options = MQGMO_WAIT
gmo.WaitInterval = MQWI_UNLIMITED
q.Get qMsg, gmo
End Sub
I'd be very grateful for any hints about what could be wrong.
Thanks
Bernard |
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| yortch |
| Posted: Mon Apr 02, 2007 9:52 am Post subject: |
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Apprentice
Joined: 30 Aug 2004
Posts: 34
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I think you need to initialize the mqmessage instance before trying to get it. Try:
| Code: |
Set qMsg = New MQMessage
Call GetQueue(q, qMsg)
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| bathouin |
| Posted: Mon Apr 02, 2007 10:20 am Post subject: |
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Newbie
Joined: 02 Apr 2007
Posts: 3
Location: Switzerland
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| yortch wrote: |
I think you need to initialize the mqmessage instance before trying to get it. Try:
| Code: |
Set qMsg = New MQMessage
Call GetQueue(q, qMsg)
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YES, brilliant, it works.
HOWEVER, on the LAST message (which of course is the only one I'm interested in...), the q.Get never returns ! The hourglass comes up, and nothing happens !? What can that be due to ? How can I avoid that behavious anyway ?
Regards
bernard |
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| yortch |
| Posted: Mon Apr 02, 2007 10:38 am Post subject: |
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Apprentice
Joined: 30 Aug 2004
Posts: 34
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| That's because you have your code to wait indefinitely, you should set a small wait interval, which if you do, you'll need to catch an exception thrown when there are no more messages in the queue. Or you could check the queue depth instead. |
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| bathouin |
| Posted: Mon Apr 02, 2007 10:46 am Post subject: |
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Newbie
Joined: 02 Apr 2007
Posts: 3
Location: Switzerland
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| yortch wrote: |
| That's because you have your code to wait indefinitely, you should set a small wait interval, which if you do, you'll need to catch an exception thrown when there are no more messages in the queue. Or you could check the queue depth instead. |
Yes, I change my _WAIT to NO_WAIT and my WaitInterval to 1000. I saw somewhere how I can trap the MQ Exceptions, now I don't find it anymore. Can you help me there ?
Thanks
Bernard |
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| yortch |
| Posted: Mon Apr 02, 2007 11:50 am Post subject: |
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Apprentice
Joined: 30 Aug 2004
Posts: 34
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This isn't VB .NET, is it? If it is, you need a try/catch clause, otherwise something like: "On Error Resume Next"
The "MQ API Support" may be a better place to find answers to these questions: http://www.mqseries.net/phpBB2/viewforum.php?f=6 |
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| Michael Dag |
| Posted: Mon Apr 02, 2007 12:03 pm Post subject: |
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Jedi Knight
Joined: 13 Jun 2002
Posts: 2607
Location: The Netherlands (Amsterdam)
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| bathouin wrote: |
| yortch wrote: |
| That's because you have your code to wait indefinitely, you should set a small wait interval, which if you do, you'll need to catch an exception thrown when there are no more messages in the queue. Or you could check the queue depth instead. |
Yes, I change my _WAIT to NO_WAIT and my WaitInterval to 1000. I saw somewhere how I can trap the MQ Exceptions, now I don't find it anymore. Can you help me there ?
Thanks
Bernard |
check the value of GetQueue.CompletionCode and GetQueue.ReasonCode
_________________
Michael
MQSystems Facebook page |
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| jefflowrey |
| Posted: Mon Apr 02, 2007 12:06 pm Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
Posts: 19981
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Also, I think when you set the MQGMO to NO_WAIT, you told it to ignore your WaitInterval.
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I am *not* the model of the modern major general. |
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