Reading Messages in a Dead Letter Queue

Reading messages in a dead letter queue is typically a three-function operation: a call to MQGetMachineProperties to retrieve the local computer identifier (its machine GUID), a call to MQOpenQueue to open the queue with receive access, and a call to MQReceiveMessage to read the message.

To read a message in a dead letter queue

1. Define an MQQMProps structure that includes PROPID_QM_MACHINE_ID.

   MQQMPROPS QMProps;
   MQPROPVARIANT Variant;
   MSGPROPID PropId;
   GUID    guidMachineId;
       
   PropId = PROPID_QM_MACHINE_ID;                 //PropId
   Variant.vt = VT_CLSID;                         //Type
   Variant.puuid = &guidMachineId;                //Value
       
   QMProps.cProp = 1;                //Number of properties.
   QMProps.aPropID = &PropId;        //Id of property.
   QMProps.aPropVar = &Variant;      //Value of property.
   QMProps.aStatus  = NULL;          //No Error report.
    

2. Call MQGetMachineProperties to retrieve the machine identifier (PROPID_QM_MACHINE_ID) of the local computer.

   hr = MQGetMachineProperties(
           NULL,
           NULL,
           &QMProps	
           );
   if (FAILED(hr))
    

3. Translate the machine GUID into a string.

   WCHAR wszMachineGuid[40];
   TBYTE* pszUuid = 0;
   if(UuidToString(&guidMachineId, &pszUuid) != RPC_S_OK)
   {
     //  Handle failure
   }
   else
   {
       wcscpy( wszMachineGuid, pszUuid );
       RpcStringFree(&pszUuid);
   }
    

4. Prepare the format name of the dead letter queue.

   wsprintf( wszFormatNameBuffer,
             L"MACHINE=%s%s",
             wszMachineGuid,
             L";DEADLETTER"
             );
    

5. Call MQOpenQueue and open the queue with receive access.

   QUEUEHANDLE hQueue;
       
   hr = MQOpenQueue(
       wszFormatNameBuffer,
       MQ_RECEIVE_ACCESS,
       0,
       &hQueue
       );
   if (FAILED(hr))
    

6. Define an MQMSGProps structure for the message properties to be retrieved.

   MQMSGPROPS MsgProps;
   MQPROPVARIANT aVariant[10];
   MSGPROPID aPropId[10];
   DWORD PropIdCount = 0;
       
   // Prepare property array (PROPVARIANT).
   #define MSG_BODY_LEN	500
   unsigned char ucMsgBody[MSG_BODY_LEN];
   DWORD dwAppspecificIndex;
       
   // Set the PROPID_M_BODY property.
   aPropId[PropIdCount] = PROPID_M_BODY;                 //PropId
   aVariant[PropIdCount].vt = VT_VECTOR|VT_UI1;          //Type
   aVariant[PropIdCount].caub.cElems = MSG_BODY_LEN;     //Value
   aVariant[PropIdCount].caub.pElems = ucMsgBody;
      
   PropIdCount++;
       
   // Set the MQMSGPROPS structure
   MsgProps.cProp = PropIdCount;       //Number of properties.
   MsgProps.aPropID = aPropId;         //Ids of properties.
   MsgProps.aPropVar = aVariant;       //Values of properties.
   MsgProps.aStatus  = NULL;           //No Error report.
    
    

7. Call MQReceiveMessage and retrieve the messages in the queue. The following call retrieves the first message in the queue.

   hr = MQReceiveMessage(
        hQueue,               // handle to the Queue.
        5 * 60 * 1000,        // Max time (msec) to wait for message.
        MQ_ACTION_RECEIVE,    // Action.
        &MsgProps,            // properties to retrieve.
       NULL,                  // No overlapped structure.
       NULL,                  // No callback function.
       NULL,                  // NO cursor.
       NULL                   // No transaction
       );
   if (FAILED(hr))
    

Example

The following example opens a dead letter queue and retrieves the message body of the first message in the queue.

    HRESULT hr;
    #define FORMAT_NAME_LEN 80
    WCHAR wszFormatNameBuffer[ FORMAT_NAME_LEN];
     
    //////////////////////////////////
    //  Define an MQQMPROPS structure 
    //  for PROPID_QM_MACHINE_ID.
    //////////////////////////////////
    
    MQQMPROPS QMProps;
    MQPROPVARIANT Variant;
    MSGPROPID PropId;
    GUID    guidMachineId;
    
    // Set the PROPID_QM_MACHINE_ID property.
    PropId = PROPID_QM_MACHINE_ID;                 //PropId
    Variant.vt = VT_CLSID;                         //Type
    Variant.puuid = &guidMachineId;                //Value
    
    // Set the MQQMPROPS structure
    QMProps.cProp = 1;                //Number of properties.
    QMProps.aPropID = &PropId;        //Id of properties.
    QMProps.aPropVar = &Variant;      //Value of properties.
    QMProps.aStatus  = NULL;          //No Error report.
    
    
    /////////////////////////////////////
    //  Retrieving the identifier of the 
    //  local computer (machine GUID).
    //////////////////////////////////////
    hr = MQGetMachineProperties(
           NULL,
           NULL,
           &QMProps 
           );
    if (FAILED(hr))
    {
        //
        //  Handle failure
        //
    }
    
    
    ///////////////////////////////////
    //  Translating the machine GUID
    //  into a string
    //////////////////////////////////
    WCHAR wszMachineGuid[40];
    WBYTE* pszUuid = 0;
    if(UuidToString(&guidMachineId, &pszUuid) != RPC_S_OK)
    {
        //
        //  Handle failure
        //
    }
    else
    {
        wcscpy( wszMachineGuid, pszUuid );
        RpcStringFree(&pszUuid);
    }
    
    
    ////////////////////////////////
    //  Preparing the format name of
    //  the dead letter queue.
    ///////////////////////////////
    wsprintf( wszFormatNameBuffer,
              L"MACHINE=%s%s",
              wszMachineGuid,
              L";DEADLETTER"
              );
    
    
    //////////////////////////////
    //  Open the queue for receive
    //////////////////////////////
    
    QUEUEHANDLE hQueue;
    
    hr = MQOpenQueue(
        wszFormatNameBuffer,
        MQ_RECEIVE_ACCESS,
        0,
        &hQueue
        );
    if (FAILED(hr))
    {
        //
        //  Handle failure
        //
    }
 
    //////////////////////////////////
    //  Define an MQMSGPROPS structure 
    //  for the message properties to 
    //  be retrieved.
    //////////////////////////////////
    
    MQMSGPROPS MsgProps;
    MQPROPVARIANT aVariant[10];
    MSGPROPID aPropId[10];
    DWORD PropIdCount = 0;
    
    // Prepare property array (PROPVARIANT).
    #define MSG_BODY_LEN	500
    unsigned char ucMsgBody[MSG_BODY_LEN];
    DWORD dwAppspecificIndex;
    
    // Set the PROPID_M_BODY property.
    aPropId[PropIdCount] = PROPID_M_BODY;                 //PropId
    aVariant[PropIdCount].vt = VT_VECTOR|VT_UI1;          //Type
    aVariant[PropIdCount].caub.cElems = MSG_BODY_LEN;     //Value
    aVariant[PropIdCount].caub.pElems = ucMsgBody;
    
    PropIdCount++;
    
    // Set the MQMSGPROPS structure
    MsgProps.cProp = PropIdCount;       //Number of properties.
    MsgProps.aPropID = aPropId;         //Ids of properties.
    MsgProps.aPropVar = aVariant;       //Values of properties.
    MsgProps.aStatus  = NULL;           //No Error report.
 
 
    /////////////////////////////////////
    // Read first message in dead 
    // letter queue.
    /////////////////////////////////////
 
    hr = MQReceiveMessage(
         hQueue,               // handle to the Queue.
         5 * 60 * 1000,        // Max time (msec) to wait for message.
         MQ_ACTION_RECEIVE,    // Action.
         &MsgProps,            // properties to retrieve.
        NULL,                  // No overlapped structure.
        NULL,                  // No callback function.
        NULL,                  // NO cursor.
        NULL                   // No transaction
        );
    if (FAILED(hr))
    {
    //
    //  Handle failure
    //
    }
 

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