Following code can NOT be compiled successfully, according the comment in boost source code I note that the compiler complains the outer state does not have inner state. I want to know how to indicate one state have a inner state, if it didn't have a initial state? Thanks! #include <boost/statechart/state_machine.hpp> #include <boost/statechart/state.hpp> namespace fsm = boost::statechart; class HandlingFileState; class PlayerFsm : public fsm::state_machine< PlayerFsm, HandlingFileState > {}; class HandlingFileState: public fsm::state< HandlingFileState, PlayerFsm/*, PlayingState*/> //if the initial state is uncoment, it can be compiled success. But I don't want this. {}; class NormalPlayingState; class PlayingState: public fsm::state< PlayingState, HandlingFileState, NormalPlayingState > {}; class NormalPlayingState: public fsm::state< NormalPlayingState, PlayingState> {}; int main() { PlayerFsm fsm; } ------ Build started: Project: TestFsm, Configuration: Debug Win32 ------ Compiling... test_fsm.cpp d:\3rd_lib\boost_1_46_1\include\boost-1_46_1\boost\statechart\simple_state.hpp(387) : error C2027: use of undefined type 'boost::STATIC_ASSERTION_FAILURE<x>' with [ x=false ] d:\3rd_lib\boost_1_46_1\include\boost-1_46_1\boost\statechart\state.hpp(30) : see reference to class template instantiation 'boost::statechart::simple_state<MostDerived,Context,InnerInitial,historyMode>' being compiled with [ MostDerived=PlayingState, Context=HandlingFileState, InnerInitial=NormalPlayingState, historyMode=has_no_history ] d:\bzhu\code\trunk\testfsm\test_fsm.cpp(16) : see reference to class template instantiation 'boost::statechart::state<MostDerived,Context,InnerInitial>' being compiled with [ MostDerived=PlayingState, Context=HandlingFileState, InnerInitial=NormalPlayingState ] Build log was saved at "file://d:\bzhu\Code\trunk\TestFsm\Debug\BuildLog.htm" TestFsm - 1 error(s), 0 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== and the first error point to : // If you receive a // "use of undefined type 'boost::STATIC_ASSERTION_FAILURE<x>'" or similar // compiler error here then either this state resides in a non-existent // orthogonal region of the outer state or the outer state does not have // inner states. BOOST_STATIC_ASSERT( ( mpl::less< orthogonal_position, typename context_type::no_of_orthogonal_regions >::value ) );