This property is available for MSMQ 2.0 and later.

It is used by receiving applications to verify that a message was sent from a specific transaction.

The transaction identifier is a 20-byte identifier that includes the following:

• The computer identifier of the sending machine (the first 16 bits)
  
  
• A transaction sequence number (the last 4 bytes)
  
  

Transaction identifiers are not guaranteed to be unique because the transaction sequence numbers are not persistent and they start over again at 2^20.

Message Queuing guarantees only that subsequent transactions will have different transaction sequence numbers.

To verify transaction boundaries, use PROPID_M_XACTID with the following properties:

• PROPID_M_FIRST_IN_XACT, which checks the first message sent in a transaction
  
  
• PROPID_M_LAST_IN_XACT, which checks the last message sent in a transaction
  
  

The following code example shows how PROPID_M_XACTID is specified in the MQMSGPROPSstructure.

	Copy Code
DWORD dwIdBufferSize = 1024; UCHAR *pucIdBuffer = (UCHAR *)malloc(dwIdBufferSize); if (pucIdBuffer == NULL) { // Error handling code (not included for clarity) } aMsgPropId[i] = PROPID_M_XACTID; // Property ID aPropVar[i].vt = VT_VECTOR|VT_UI1; // Type indicator aPropVar[i].caub.pElems = (UCHAR*)pucIdBuffer; aPropVar[i].caub.cElems = dwIdBufferSize; i++;