Dequeuing Messages

This topic includes examples for dequeuing RAW (string of characters) and user-defined type messages.

Note: For more information about sample code, see Sample Code and Applications.

Dequeuing RAW (string of characters) Messages:

#include <oracl.h>

OSession osess ;
int DequeueRaw();
int main(int argc, char **argv)
{
        int retVal = 0;
        OStartup(OSTARTUP_MULTITHREADED);
        try
        {
                osess.Open();
                if ( ! osess.IsOpen() )
                {
                        cout <<  "Session not opened: Error:
                              " << osess.GetErrorText() << endl;
                        osess.Close();
                        OShutdown();
                        return -1;
                }
                retVal =  DequeueRaw();
        }
        catch(OException oerr)
        {
                cout << "Exception while dequeuing message : " 
                        << oerr.GetErrorText() << endl;
                retVal =  -1;
        }
        OShutdown();
        return retVal;
}


// This function dequeues a message of default 
// type (string of characters) from the raw_msg_queue.

// Gets the message priority after dequeuing
// Checks if any message with correlation like 'AQ' is available 
// on the queue.
int DequeueRaw()
{
        ODatabase odb;
        OAQ  oaq;
        OAQMsg oaqmsg;
        OValue msg;
        const char *msgid = 0;

        odb.Open(osess, "ExampleDB", "SCOTT", "TIGER");

        // Open the 'raw_msg_queue'
        oaq.Open(odb,"raw_msg_queue");
       
        // Get an instance of the default message(of RAW type)
        oaqmsg.Open(oaq);

        // Dequeue a message 
        msgid = oaq.Dequeue();
      
        // Retrieve the message attributes
        oaqmsg.GetValue(&msg);
        const char *msgval = msg;
        cout <<"Message '"<<msgval<<"' dequeued at 
                      priority : "<<oaqmsg.GetPriority()<<endl;
        // Dequeue message with correlation like "AQ"
        oaq.SetCorrelate("%AQ%");
        oaq.SetDequeueMode(OAQ_DQ_REMOVE);
        msgid = oaq.Dequeue();
       
        // Retrieve the message attributes
       char msgval[101];
        long len = oaqmsg.GetValue(msgval,100);
        msgval[len] = '\0';
        cout<<"Message '"<<msgval<<"' dequeued at 
                       priority : "<<oaqmsg.GetPriority()<<endl;
       //Close all of the objects
        oaqmsg.Close();
        oaq.Close();
        odb.Close();
        return 0;
}

Dequeuing User-Defined Type Messages:

// This function dequeues a message of user-defined type MESSAGE_TYPE
// from the msg_queue.

// Gets the message priority after dequeuing
// Checks if any message with correlation like 'SCOTT' is available on 
// the queue.
int DequeueObject()
{
        ODatabase odb;
        OAQ  oaq;
        OAQMsg oaqmsg;
        const char *msgid = 0;
        OValue msg;
        char subject[255];
        char text[255];

        odb.Open(osess, "ExampleDB", "SCOTT", "TIGER");

        // Open the 'msg_queue'
        oaq.Open(odb,"msg_queue");
     
        // Get an instance of the udt MESSAGE_TYPE (check out schema
        //for details)
        oaqmsg.Open(oaq, OTYPE_OBJECT, "MESSAGE_TYPE");

        // Dequeue message with correlation like "SCOTT"
        oaq.SetCorrelate("%SCOTT%");
        oaq.SetDequeueMode(OAQ_DQ_REMOVE);
        msgid = oaq.Dequeue();
      
        // Retrieve the message attributes
        // Get the subject,text attributes of the message
        OObject msgval;
        oaqmsg.GetValue(&msgval);
        msgval.GetAttrValue("subject", subject,255);    
        msgval.GetAttrValue("text", text,255);

        cout<<"Message '"<<(subject ? subject :"")<<"' & Body : '"<<text<<"
                 'dequeued at priority : "<<oaqmsg.GetPriority()<<endl;

        msgid = 0;
        oaq.SetNavigation(OAQ_DQ_FIRST_MSG);
        oaq.SetCorrelate("");

        // Dequeue a message 
        msgid = oaq.Dequeue();
       
              // Retrieve the message attributes
              OObject msgval;
              oaqmsg.GetValue(&msg);
              msgval = msg;     
            
              // Get the subject,text attributes of the message
              msgval.GetAttrValue("subject", subject,255);    
              msgval.GetAttrValue("text", text,255);
              cout<<"Message '"<<(subject ? subject :"")<<"' & Body :
                         '"<<text<<"' dequeued at priority : "<<oaqmsg.GetPriority()<<endl;
       
        // Close all of the objects
        oaqmsg.Close();
        oaq.Close();
        odb.Close();
        return 0;

}