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Hierarchical State Machine Design in C++

By Dmitry Babitsky, December 01, 2005

In a Hierarchical Finite State Machine, any state can be a substate of some larger state. Dmitry presents a class that implements this pattern.

December, 2005: Hierarchical State Machine Design in C++

Figure 2: A sample run that shows what's going on, generated by the announcer class template.

class Pelican::pedestriansFlash +(this=0x411bb9)->
  vehiclesEnabled::on_enter->vehiclesGreen::on_enter
class Pelican::vehiclesGreenInt derives from class Pelican::vehiclesGreen ?
  -NO->vehiclesGreen::on_exit
class Pelican::vehiclesGreenInt derives from class Pelican::vehiclesEnabled ?
  -YES-stay in vehiclesEnabled
class Pelican::vehiclesGreen derives from class Pelican::vehiclesGreenInt ?-NO
class Pelican::vehiclesGreen derives from class Pelican::vehiclesEnabled ?
  -YES-already in vehiclesEnabled->vehiclesGreenInt::on_enter
class Pelican::vehiclesYellow derives from class Pelican::vehiclesEnabled ?
  -YES-stay in vehiclesEnabled
class Pelican::vehiclesGreenInt derives from class Pelican::vehiclesYellow ?-NO
class Pelican::vehiclesGreenInt derives from class Pelican::vehiclesEnabled ?
  -YES-already in vehiclesEnabled->vehiclesYellow::on_enter
class Pelican::pedestriansWalk derives from class Pelican::vehiclesYellow ?
  -NO->vehiclesYellow::on_exit
class Pelican::pedestriansWalk derives from class Pelican::vehiclesEnabled ?
  -NO->vehiclesEnabled::on_exit
class Pelican::vehiclesYellow derives from class Pelican::pedestriansWalk ?-NO
class Pelican::vehiclesYellow derives from class Pelican::pedestriansEnabled ?
  -NO->pedestriansEnabled::on_enter->pedestriansWalk::on_enter
class Pelican::pedestriansFlash derives from class Pelican::pedestriansWalk ?
  -NO->pedestriansWalk::on_exit
class Pelican::pedestriansWalk derives from class Pelican::pedestriansFlash ?-NO
class Pelican::pedestriansWalk derives from class Pelican::pedestriansEnabled ?
  -YES-already in pedestriansEnabled->pedestriansFlash::on_enter
class Pelican::vehiclesGreen derives from class Pelican::pedestriansFlash ?
  -NO->pedestriansFlash::on_exit
class Pelican::pedestriansFlash derives from class Pelican::vehiclesGreen ?-NO
class Pelican::pedestriansFlash derives from class Pelican::vehiclesEnabled ?
  -NO->vehiclesEnabled::on_enter-



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