DataWriter Use Cases
[Programming How-To's]

Working with data writers. More...

Setting up a data writer

• Set up publisher

• Set up a topic

• Create a data writer, FooDataWriter, of user data type Foo:

      struct DDS_DataWriterQos writer_qos = DDS_DataWriterQos_INITIALIZER;
      DDS_DataWriter* writer;
      struct DDS_DataWriterListener writer_listener =
          DDS_DataWriterListener_INITIALIZER;
  
      /* MyWriterListener_* functions are user defined to match
         DDS_DataWriterListener functions */
      writer_listener.on_offered_deadline_missed =
          MyWriterListener_OfferedDeadlineMissed;
      writer_listener.on_offered_incompatible_qos =
          MyWriterListener_OfferedIncompatibleQos;
      writer_listener.on_liveliness_lost = MyWriterListener_LivelinessLost;
      writer_listener.on_publication_match = MyWriterListener_PublicationMatch;
  
      retcode = DDS_Publisher_get_default_datawriter_qos(publisher, &writer_qos);
  
      if (retcode != DDS_RETCODE_OK) {
          printf("***Error: failed to get default datawriter qos\n");
      }
  
      writer = DDS_Publisher_create_datawriter(publisher, 
                                               topic, 
                                               &writer_qos, 
                                               &writer_listener /* or NULL */,
                                               DDS_STATUS_MASK_ALL);
  
      if (writer == NULL) {
          printf("***Error: failed to create writer\n");
      }
  

Managing instances

• Getting an instance "key" value of user data type Foo

    struct Foo* data = ...;     /* user data */
  
    retcode = FooDataWriter_get_key_value(writer, data, &instance_handle);
  
    if (retcode != DDS_RETCODE_OK) {
        /* ... check for cause of failure */
    }    
  

• Registering an instance of type Foo

    DDS_InstanceHandle_t instance_handle = DDS_HANDLE_NIL;
  
    instance_handle = FooDataWriter_register_instance(writer, data);
  

• Unregistering an instance of type Foo

    retcode = FooDataWriter_unregister_instance(writer, data, &instance_handle);
  
    if (retcode != DDS_RETCODE_OK) {
        /* ... check for cause of failure */
    }  
  

• Disposing of an instance of type Foo

    retcode = FooDataWriter_dispose(writer, data, &instance_handle);
  
    if (retcode != DDS_RETCODE_OK) {
        /* ... check for cause of failure */
    }  
  

Sending data

• Set up data writer

• Register instance

• Write instance of type Foo

    struct Foo* data = ...;     /* user data */
  
    DDS_InstanceHandle_t instance_handle = 
        DDS_HANDLE_NIL; /* or a valid registered handle */
  
    DDS_ReturnCode_t retcode;
  
    retcode = FooDataWriter_write(writer, data, &instance_handle);
  
    if (retcode != DDS_RETCODE_OK) {
        /* ... check for cause of failure */
    }
  

Tearing down a data writer

• Delete DDS_DataWriter:

      DDS_ReturnCode_t retcode;
  
      retcode = DDS_Publisher_delete_datawriter(publisher, writer);
  
      if (retcode != DDS_RETCODE_OK) {
          printf("***Error: failed to delete writer\n");
      }