what c++ code can i use?

[Your Computer]

What do you mean by saying that should be more practical for HPL3?

HPL2 only saves the state of variables using the SetLocalVar/SetGlobalVar functions. States of classes aren't saved, and certain features can't be used (import functions).

Also, the current functions of HPL2 that deal with callbacks may not be capable of handling object handles. I say "may not" because i haven't tested it out yet, but given that you are passing a string to the callback parameter, it should be safe to assume that it won't properly handle object handles.