How to return data on my define the type_data?

[Tysonliang]

First，i have a topictype: TPC_Hello_world
Second, i instance a topicdata： m_topic_data = TPC_Hello_world()
I expect that listen the TPC_Hello_world data and trans to m_topic_data.
if i expect the m_topic_data address is not change.
How to do ？