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Subscriber

The |Subscriber-api| acts on behalf of one or several :ref:`dds_layer_subscriber_dataReader` objects that belong to it. It serves as a container that allows grouping different DataReader objects under a common configuration given by the :ref:`dds_layer_subscriber_subscriberQos` of the Subscriber.

DataReader objects that belong to the same Subscriber do not have any other relation among each other beyond the |SubscriberQos-api| of the Subscriber and act independently otherwise. Specifically, a Subscriber can host DataReader objects for different topics and data types.

SubscriberQos

|SubscriberQos-api| controls the behavior of the :ref:`dds_layer_subscriber_subscriber`. Internally it contains the following |QosPolicy-api| objects:

QosPolicy class Accessor/Mutator Mutable
|presentationqospolicy| |SubscriberQos::presentation-api| Yes
|partitionqospolicy| |SubscriberQos::partition-api| Yes
|groupdataqospolicy| |SubscriberQos::group_data-api| Yes
|entityfactoryqospolicy| |SubscriberQos::entity_factory-api| Yes

Refer to the detailed description of each |QosPolicy-api| class for more information about their usage and default values.

The QoS value of a previously created Subscriber can be modified using the |Subscriber::set_qos-api| member function.

.. literalinclude:: /../code/DDSCodeTester.cpp
   :language: c++
   :start-after: //DDS_CHANGE_SUBSCRIBERQOS
   :end-before: //!
   :dedent: 8

Default SubscriberQos

The default :ref:`dds_layer_subscriber_subscriberQos` refers to the value returned by the |DomainParticipant::get_default_subscriber_qos-api| member function on the :ref:`dds_layer_domainParticipant` instance. The special value SUBSCRIBER_QOS_DEFAULT can be used as QoS argument on |DomainParticipant::create_subscriber-api| or |Subscriber::set_qos-api| member functions to indicate that the current default SubscriberQos should be used.

When the system starts, the default SubscriberQos is equivalent to the default constructed value |SubscriberQos::SubscriberQos-api|. The default SubscriberQos can be modified at any time using the |DomainParticipant::set_default_subscriber_qos-api| member function on the DomainParticipant instance. Modifying the default SubscriberQos will not affect already existing Subscriber instances.

.. literalinclude:: /../code/DDSCodeTester.cpp
   :language: c++
   :start-after: //DDS_CHANGE_DEFAULT_SUBSCRIBERQOS
   :end-before: //!
   :dedent: 8

|DomainParticipant::set_default_subscriber_qos-api| member function also accepts the special value SUBSCRIBER_QOS_DEFAULT as input argument. This will reset the current default SubscriberQos to default constructed value |SubscriberQos::SubscriberQos-api|.

.. literalinclude:: /../code/DDSCodeTester.cpp
   :language: c++
   :start-after: //DDS_CHANGE_SUBSCRIBERQOS_TO_DEFAULT
   :end-before: //!
   :dedent: 8

Note

The value SUBSCRIBER_QOS_DEFAULT has different meaning depending on where it is used: