Dynamic content filtering in opendds for subscriber?

Question

I'm using openDDS for Data-centric publish subscribe model. Publisher is continuously sending data and subscriber will receive it.but in the case of subscriber ,it has to receive filtered data based on the condition I have given.

suppose my topic structure used by both publisher and subscriber is :

module Messenger {

#pragma DCPS_DATA_TYPE "Messenger::ChannelData"
#pragma DCPS_DATA_KEY "Messenger::ChannelData subject_id"

  struct ChannelData {
            string from;
            string subject;
            long subject_id;
            string text;
            long   count;
  };
};

OpenDDS has one concept named as content-filtering topic. same I have used.

Code :

  // Register Type (Messenger::Message)
    Messenger::ChannelDataTypeSupport_var ts =
      new Messenger::ChannelDataTypeSupportImpl();

    if (ts->register_type(participant.in(), "") != DDS::RETCODE_OK) {
      ACE_ERROR_RETURN((LM_ERROR,
                        ACE_TEXT("%N:%l main()")
                        ACE_TEXT(" ERROR: register_type() failed!\n")), -1);
    }

    // Create Topic (Movie Discussion List)
    CORBA::String_var type_name = ts->get_type_name();
    DDS::Topic_var topic =
      participant->create_topic("Movie Discussion List",
                                type_name.in(),
                                TOPIC_QOS_DEFAULT,
                                DDS::TopicListener::_nil(),
                                OpenDDS::DCPS::DEFAULT_STATUS_MASK);

 DDS::ContentFilteredTopic_var cft =
         participant->create_contentfilteredtopic("MyTopic-Filtered",
         topic,
         "count <= 0 ",DDS::StringSeq());

But In above code I have hard coded filter condition count <=0 .

so,is there any way to provide dynamic filter condition for subscriber to receive filtered data?

Answer 1

Instead of 0 pass %0 and instead of DDS::StringSeq() pass a sequence of length 1 that contains the value that should be used for %0. A quick search on google would have given you several examples!