The get_discovered_participants() operation provides you with a list of DomainParticipants that have been discovered in the DDS domain (except any that you have said to ignore via the ignore_participant() operation (see Restricting Communication—Ignoring Entities)).
Once you have a list of discovered DomainParticipants, you can get more information about them by calling the get_discovered_participant_data() operation. This operation can only be used on DomainParticipants that are in the same DDS domain and have not been marked as ‘ignored.’ Otherwise, the operation will fail and return DDS_RETCODE_PRECONDITION_NOT_MET. The returned information is of type DDS_ParticipantBuiltinTopicData, described in Participant Built-in Topic’s Data Type (DDS_ParticipantBuiltinTopicData).
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