DataWriters

You are here: Part 2: Core Concepts > Sending Data > DataWriters

DataWriters

To create a DataWriter, you need a DomainParticipant and a Topic.

You need a DataWriter for each Topic that you want to publish. Once you have a DataWriter, you can use it to perform the operations listed in . The most important operation is write(), described in Writing Data. For more details on all operations, see the API Reference HTML documentation.

DataWriters are created by using operations on a DomainParticipant or a Publisher, as described in Creating DataWriters. If you use the DomainParticipant’s operations, the DataWriter will belong to an implicit Publisher that is automatically created by the middleware. If you use a Publisher’s operations, the DataWriter will belong to that Publisher. So either way, the DataWriter belongs to a Publisher.

Note: Some operations cannot be used within a listener callback, see Restricted Operations in Listener Callbacks.

DataWriter Operations
Working with ...	Operation	Description	Reference
DataWriters	assert_liveliness	Manually asserts the liveliness of the DataWriter.	Asserting Liveliness
	enable	Enables the DataWriter.	Enabling DDS Entities
	equals	Compares two DataWriter’s QoS structures for equality.	Comparing QoS Values
	get_qos	Gets the QoS.	Setting DataWriter QosPolicies
	lookup_instance	Gets a handle, given an instance. (Useful for keyed data types only.)	Looking Up an Instance Handle
	set_qos	Modifies the QoS.	Setting DataWriter QosPolicies
	set_qos_with_profile	Modifies the QoS based on a QoS profile.	Setting DataWriter QosPolicies
	get_listener	Gets the currently installed Listener.	Setting Up DataWriterListeners
	set_listener	Replaces the Listener.	Setting Up DataWriterListeners
FooDataWriter (See Using a Type-Specific DataWriter (FooDataWriter))	dispose	States that the instance no longer exists. (Useful for keyed data types only.)	Disposing of Data
	dispose_w_timestamp	Same as dispose, but allows the application to override the automatic source_timestamp. (Useful for keyed data types only.)	Disposing of Data
	flush	Makes the batch available to be sent on the network.	Flushing Batches of DDS Data Samples
	get_key_value	Maps an instance_handle to the corresponding key.	Getting the Key Value for an Instance
	narrow	A type-safe way to cast a pointer. This takes a DDSDataWriter pointer and ‘narrows’ it to a ‘FooDataWriter’ where ‘Foo’ is the related data type.	Using a Type-Specific DataWriter (FooDataWriter)
	register_instance	States the intent of the DataWriter to write values of the data-instance that matches a specified key. Improves the performance of subsequent writes to the instance. (Useful for keyed data types only.)	Registering and Unregistering Instances
	register_instance_w_ timestamp	Like register_instance, but allows the application to override the automatic source_timestamp. (Useful for keyed data types only.)
	unregister_instance	Reverses register_instance. Relinquishes the ownership of the instance. (Useful for keyed data types only.)
	unregister_instance_w_ timestamp	Like unregister_instance, but allows the application to override the automatic source_timestamp. (Useful for keyed data types only.)
	write	Writes a new value for a data-instance.	Writing Data
	write_w_timestamp	Same as write, but allows the application to override the automatic source_timestamp.	Writing Data
FooDataWriter (See Using a Type-Specific DataWriter (FooDataWriter))	write_w_params	Same as write, but allows the application to specify parameters such as source timestamp and instance handle.	Writing Data
	dispose_w_params	Same as dispose, but allows the application to specify parameters such as source timestamp and instance handle..	Disposing of Data
	register_w_params	Same as register, but allows the application to specify parameters such as source timestamp, instance handle.	Registering and Unregistering Instances
	unregister_w_params	Same as unregister, but allows the application to specify parameters such as source timestamp, and instance handle.	Registering and Unregistering Instances
Matched Subscriptions	get_matched_ subscriptions	Gets a list of subscriptions that have a matching Topic and compatible QoS. These are the subscriptions currently associated with the DataWriter.	Finding Matching Subscriptions
	get_matched_ subscription_data	Gets information on a subscription with a matching Topic and compatible QoS.
	get_matched_ subscription_locators	Gets a list of locators for subscriptions that have a matching Topic and compatible QoS. These are the subscriptions currently associated with the DataWriter.
	get_matched_ subscription_ participant_data	Gets information about the DomainParticipant of a matching subscription.	Finding the Matching Subscription’s ParticipantBuiltinTopicData
Status	get_status_changes	Gets a list of statuses that have changed since the last time the application read the status or the listeners were called.	Getting Status and Status Changes
	get_liveliness_lost_status	Gets LIVELINESS_LOST status.	Statuses for DataWriters
	get_offered_deadline_ missed_status	Gets OFFERED_DEADLINE_MISSED status.
	get_offered_ incompatible_qos_status	Gets OFFERED_INCOMPATIBLE_QOS status.
	get_publication_match_ status	Gets PUBLICATION_MATCHED_QOS status.
Status cont'd	get_reliable_writer_ cache_changed_status	Gets RELIABLE_WRITER_CACHE_CHANGED status
	get_reliable_reader_ activity_changed_status	Gets RELIABLE_READER_ACTIVITY_CHANGED status
	get_datawriter_cache_ status	Gets DATA_WRITER_CACHE_status
	get_datawriter_protocol_status	Gets DATA_WRITER_PROTOCOL status
	get_matched_ subscription_datawriter_protocol_status	Gets DATA_WRITER_PROTOCOL status for this DataWriter, per matched subscription identified by the subscription_handle.	Statuses for DataWriters
	get_matched_ subscription_datawriter_protocol_status_ by_locator	Gets DATA_WRITER_PROTOCOL status for this DataWriter, per matched subscription as identified by a locator.	Statuses for DataWriters
Other	get_publisher	Gets the Publisher to which the DataWriter belongs.	Finding Related DDS Entities
	get_topic	Get the Topic associated with the DataWriter.	Finding Related DDS Entities
	wait_for_ acknowledgements	Blocks the calling thread until either all data written by the DataWriter is acknowledged by all matched Reliable DataReaders, or until the a specified timeout duration, max_wait, elapses.	Waiting for Acknowledgments in a DataWriter