Looking for C++ FSM classes for embedded project

Question

I'd like some (freely reusable) C++ classes to represent states, events and Finite State Machines (FSM).

Maybe each even has a unique ID and string name which can be used when debugging. Maybe each state has the same plus an OnEnter() and OnExit() function, etc and maybe each FSM has a collection of states, each of which accepts various events.

Before I code my own, is there anything available off the shelf? I was thinking about Boost, but they are a little cagey about using it in embedded systems (see http://www.boost.org/doc/libs/1_35_0/libs/statechart/doc/faq.html)

Thanks for any advice, I am ending towards coding my own, as that will meet my needs 100% but it would be silly not to look at anything that's out there for free.

Answer 1

The only C++ framework I know for modelling finite state machines is part of the Qt Toolkit (see the QStateMachine API for the entry point into the framework).

However, this is possibly overkill for you, so I'd probably model my own set of classes as well, like:

struct Event {
    int id;
    std::string name;
};

struct State;

struct Transition {
    virtual void execute() = 0;
    virtual State *newState() = 0;
};

struct State {
    virtual void onEnter() = 0;
    virtual void onExit() = 0;
    virtual Transition *getTransition( const Event &e );
};

Then you could have an initial State object and from there on call getTransition() (and check the returned transition for which state is the new state) repeatedly.

Answer 2

Free FSM libraries for C/C++ I'm aware of are:

• RWTH FSA Toolkit
• The ASTL extension of the STL (GPL).
• WFST itself is licensed under the GPL but has external dependencies like the AT&T FSM library.

The AT&T FSM libs are excellent but I'm not sure about what the license allows. Same goes for Grail.

If all you need are classes which represent states, though, I also think it's best to implement your own.

Answer 3

Try SMC - the State Machine Compiler. This lets you define a state machine using their own definition language, then generate the code for a wide range of programming languages, including C++, C#, Java, Ruby, Python, Scala, VB.Net and several others.

Answer 4

You could try Miro Samek's State Machines. http://www.state-machine.com/index.php

Finite state machine, event driven, C/C++, designed for embedded systems, and ported to many microprocessors.