Currently my queue object is a member of the state machine itself, so I can write

struct Send_ : public msm::front::state_machine_def<Send_> { string m_next_line_to_send; socket m_socket; string get_next_send_line(); };

and in my a_send action void operator()(Event &const &evt, Fsm &fsm, S&, T&) { fsm.m_next_line_to_send=fsm.get_next_send_line(); fsm.m_socket.async_write(fsm.m_next_line_to_send); }

This works well as long as I am not using sub-statemachines.

Here is my problem: I would like to use a substate machine for the actual sending. The main state machine has the states Disconnected, Working, Error, Shutdown. The Working state should actually be a substate machine.

The problem is, when a_send gets called by the substate machine Working, the fsm object is of type Working.

Correct. There is no "fsm call stack" yet. This gets complicated if you have a submachine of a submachine of ... For the moment I don't have this.

How can I access the member variables of the parent of a substate machine? Or is there a better way of accessing the objects the state machine should work with from actions?

For the moment, all we can do is adding a pointer to the main fsm's data in the submachine. It is less elegant with the 1.44 than the coming 1.45: With 1.44 (for example inside the on_entry method of Send_): Send_::Working& w = fsm.get_state<Send_::Working&>(); w.data = &fsm.data; // w.data is a pointer True, this is not really nice. With the upcoming 1.45 (or trunk for the moment), you could use the new constructors: Send myfsm (msm::back::states_ << Working(data) ); //data being externally defined and Working_ having a corresponding constructor But this won't work for your case where data is contained in Send_ (and therefore does not exist at the time of construct). You can however reuse the same syntax with the new set_states method: Replace the version with get_state by: fsm.set_states(msm::back::states_ << Working(fsm.data)); //data being defined in Send_ and Working_ having a corresponding constructor. The whole explanation is there (http://svn.boost.org/svn/boost/trunk/libs/msm/doc/HTML/ch03s05.html#backend-...).

The tutorial explains state machines very nicely with the example of a CD player. But all the actions are empty and nowhere is explained, how you would actually access a CD player member variable or other such object so that you could actually manipulate the player to do something.

Seems that I need to improve my doc here. It's too late for the 1.45 but I'll do it for the 1.46. I agree that this is still not perfect and it's on my list but the list is still pretty long so I hope this solution will be ok for the time being. Regards, Christophe