C++ State machine affecting "HAS-A Parent"

I'm trying to implement a State Machine. The State Machine will have to have an impact on the obj开发者_开发百科ect that "HAS" it as a member.

However, I obviously can't include the "StateMachine" in the "Game" class AND include the "Game" header in the "StateMachine" class.

How do I get around this problem?

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As your client class is a member rather than an inheriting daughter, you can not access any private state of the parent (which I'm sure you knew), so you have a limited number of choices:

• Expose some state in the parent publicly and diddle that (but this is poor design and should be avoided)
• Give the parent a public notification interface of some kind and use that (better then the above, but still not great)
• Pass a call-back to the client (a very c programmer type of solution)
• Use some kind of signal/slots mechanism to notify the parent that something interesting has happened. If you're using any of the big frameworks (Qt, etc...), this may already be available

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Use forward class declarations.

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Forward declare the classes; as an example:

class StateMachine;

class Game
{
    StateMachine *sm;
    // stuff
};

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To clarify a bit.

If your header file only has pointers of a type defined somewhere else, you don't need to include that header file in your header file.

instead, do a forward declaration such as class StateMachine; then include the StateMachine header file in your CPP file, after the include to your own header file.