eprosima FastDDS symbol lookup error for new function in DomainParticipant

Question

I tried to implement a new function in the eprosimas FastDDS DomainParticipant class which causes a symbol lookup error. My executable is called "Vector". It shall send a vector via DDS/RTPS. The program runs perfectly, if I don't call my new function in the DomainParticipant class

The application:

./Vector publisher

causes:

./Vector: symbol lookup error: ./Vector: undefined symbol: _ZN8eprosima7fastdds3dds17DomainParticipant11return_testB5cxx11Ev.

I broke down the problem to a simple function, so I hope you can understand. I added the following function to the DomainParticipant cpp (and hpp):

std::string DomainParticipant::return_test()
{
    return std::string("Test\n\r");
}

The function call is inside the initialization of the publisher. The parameters for the initialization are given by a xml file. My application follows the examples of eprosimas FastDDS. Most is copy&paste from other examples. If you are familiar with these, you might recognize the code snippet

bool VectorPublisher::init()
{
    // Load xml file
    if (ReturnCode_t::RETCODE_OK == 
        DomainParticipantFactory::get_instance()->load_XML_profiles_file("DEFAULT_FASTRTPS_PROFILES.xml"))
    {
        participant_ = DomainParticipantFactory::get_instance()->create_participant_with_profile(0, "participant_profile");

        if (participant_ == nullptr)
        {
            return false;
        }
        
        //REGISTER THE TYPE
        type_.register_type(participant_);

        //CREATE THE PUBLISHER
        publisher_ = participant_->create_publisher(PUBLISHER_QOS_DEFAULT, nullptr);
        if (publisher_ == nullptr)
        {
            return false;
        }

        topic_ = participant_->create_topic("VectorTopic", "Vector", TOPIC_QOS_DEFAULT);

        if (topic_ == nullptr)
        {
            return false;
        }

        // CREATE THE WRITER
        writer_ = publisher_->create_datawriter_with_profile(topic_, "datawriter_profile", &listener_);
        
        if (writer_ == nullptr)
        {
            return false;
        }
        
        
        std::string test = "this";
        // This line causes the symbol lookup error:
        test = participant_->return_test();
        std::cout << test << std::endl;
        
    }
    else
    {
        logError(VECTORPUBLISHER, "Initialization of publisher failed. Problem loading xml.");
        return false;
    }
    return true;
}

The function call of return_test() causes the error:

test = participant_->return_test();

If I comment the line, everything works fine.

I am have basic C++ skills and I have a hard time trying to understand the problem. If anyone has a hint why I get a symbol lookup error, I would appreciate it. If there are further question about my code, I can add some information. Thanks in advance.