Writing the required instance class methods

Next, we must write methods in the Instance class to implement the virtual functions declared in the parent TypeInstance class. For the derived class, its constructor must associate a reference TopicDataType object with the parent class. The DataBufferPubSubType class (which was generated by fastrtpsgen) is a specialization of TopicDataType, so a reference to this generated class can be passed into the constructor, which can assign it to the parent object:

DataBufferType::Instance::Instance( DataBufferPubSubType& type )
    : TypeInstance( type, &m_data )
{
    m_data.name( "value" );
}

The initSample() member function is responsible for initializing data samples that will be exchanged through a publication object. In our implementation, we use the assignment operator defined in the DataBuffer class (also generated by fastrtpsgen) to assign the data in the DataBufferType instance to the sample (which is referenced by a generic pointer):

void DataBufferType::Instance::initSample( void* sample, 
                                           const pips_guid_t* guid ) const
{
    DataBuffer* buf = ( DataBuffer* )sample;
    *buf = m_data;
    // TO-DO: Set the key here if using keyed types.
}

An assignment operator is required to assign the data in a sample to a DataBuffer instance. This allows subscribers (i.e., data readers) to update type instances with the received sample data:

TypeInstance& DataBufferType::Instance::operator=( const void* sample_data )
{
    if ( sample_data ) {
        m_data = *( DataBuffer* )sample_data;
    }
    return *this;
}