3.3.1. Publisher

The Publisher acts on behalf of one or several DataWriter objects that belong to it. It serves as a container that allows grouping different DataWriter objects under a common configuration given by the PublisherQos of the Publisher.

DataWriter objects that belong to the same Publisher do not have any other relation among each other beyond the PublisherQos of the Publisher and act independently otherwise. Specifically, a Publisher can host DataWriter objects for different Topics and data types.

3.3.1.1. PublisherQos

PublisherQos controls the behavior of the Publisher. Internally it contains the following QosPolicy objects:

QosPolicy class

Accessor/Mutator

Mutable

PresentationQosPolicy

presentation()

Yes

PartitionQosPolicy

partition()

Yes

GroupDataQosPolicy

group_data()

Yes

EntityFactoryQosPolicy

entity_factory()

Yes

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

The QoS value of a previously created Publisher can be modified using the Publisher::set_qos() member function.

// Create a DomainParticipant in the desired domain
DomainParticipant* participant =
        DomainParticipantFactory::get_instance()->create_participant(0, PARTICIPANT_QOS_DEFAULT);
if (nullptr != participant)
{
    // Error
    return;
}

// Create a Publisher with default PublisherQos
Publisher* publisher =
        participant->create_publisher(PUBLISHER_QOS_DEFAULT);
if (nullptr != publisher)
{
    // Error
    return;
}

// Get the current QoS or create a new one from scratch
PublisherQos qos = publisher->get_qos();

// Modify QoS attributes
// (...)

// Assign the new Qos to the object
publisher->set_qos(qos);

3.3.1.1.1. Default PublisherQos

The default PublisherQos refers to the value returned by the get_default_publisher_qos() member function on the DomainParticipant instance. The special value PUBLISHER_QOS_DEFAULT can be used as QoS argument on create_publisher() or Publisher::set_qos() member functions to indicate that the current default PublisherQos should be used.

When the system starts, the default PublisherQos is equivalent to the default constructed value PublisherQos(). The default PublisherQos can be modified at any time using the set_default_publisher_qos() member function on the DomainParticipant instance. Modifying the default PublisherQos will not affect already existing Publisher instances.

// Create a DomainParticipant in the desired domain
DomainParticipant* participant =
        DomainParticipantFactory::get_instance()->create_participant(0, PARTICIPANT_QOS_DEFAULT);
if (nullptr != participant)
{
    // Error
    return;
}

// Get the current QoS or create a new one from scratch
PublisherQos qos_type1 = participant->get_default_publisher_qos();

// Modify QoS attributes
// (...)

// Set as the new default PublisherQos
if(participant->set_default_publisher_qos(qos_type1) != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

// Create a Publisher with the new default PublisherQos.
Publisher* publisher_with_qos_type1 =
        participant->create_publisher(PUBLISHER_QOS_DEFAULT);
if (nullptr != publisher_with_qos_type1)
{
    // Error
    return;
}

// Get the current QoS or create a new one from scratch
PublisherQos qos_type2;

// Modify QoS attributes
// (...)

// Set as the new default PublisherQos
if(participant->set_default_publisher_qos(qos_type2) != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

// Create a Publisher with the new default PublisherQos.
Publisher* publisher_with_qos_type2 =
        participant->create_publisher(PUBLISHER_QOS_DEFAULT);
if (nullptr != publisher_with_qos_type2)
{
    // Error
    return;
}

// Resetting the default PublisherQos to the original default constructed values
if(participant->set_default_publisher_qos(PUBLISHER_QOS_DEFAULT)
        != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

// The previous instruction is equivalent to the following
if(participant->set_default_publisher_qos(PublisherQos())
        != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

set_default_publisher_qos() member function also accepts the special value PUBLISHER_QOS_DEFAULT as input argument. This will reset the current default PublisherQos to default constructed value PublisherQos().

// Create a DomainParticipant in the desired domain
DomainParticipant* participant =
        DomainParticipantFactory::get_instance()->create_participant(0, PARTICIPANT_QOS_DEFAULT);
if (nullptr != participant)
{
    // Error
    return;
}

// Create a custom PublisherQos
PublisherQos custom_qos;

// Modify QoS attributes
// (...)

// Create a publisher with a custom PublisherQos
Publisher* publisher = participant->create_publisher(custom_qos);
if (nullptr != publisher)
{
    // Error
    return;
}

// Set the QoS on the publisher to the default
if (publisher->set_qos(PUBLISHER_QOS_DEFAULT) != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

// The previous instruction is equivalent to the following:
if(publisher->set_qos(participant->get_default_publisher_qos())
        != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

Note

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