无法编译 FSM 示例代码

Question

Robert 有一个很好的状态机教程，名为 UML 教程：有限状态机 C.马丁. 但我无法编译它提供的示例代码。 我得到 *FsmTest.cpp(46) ：错误 C2664：'SetState'：无法将参数 1 从 'class UnlockedState *' 转换为 'class TurnstileState '

请帮忙。 谢谢。

class Turnstile
{
public:
    virtual void Lock();
    virtual void Unlock();
    virtual void Thankyou();
    virtual void Alarm();
};

class TurnstileFSM;
class LockedState;
class UnlockedState;

class TurnstileState
{
public:
    virtual void Coin(TurnstileFSM*) = 0;
    virtual void Pass(TurnstileFSM*) = 0;
protected:
    static LockedState lockedState;
    static UnlockedState unlockedState;
};

class TurnstileFSM : public Turnstile
{
public:
    void SetState(TurnstileState* s) {itsState = s;}
    void Coin() {itsState->Coin(this);}
    void Pass() {itsState->Pass(this);}


private:
    TurnstileState *itsState;
};

class LockedState : public TurnstileState
{
public:
    virtual void Coin(TurnstileFSM* t)
    {
        t->SetState(&unlockedState);
        t->Unlock();
    }
    virtual void Pass(TurnstileFSM* t)
    {
        t->Alarm();
    }
};

class UnlockedState : public TurnstileState
{
public:
    virtual void Coin(TurnstileFSM* t)
    {
        t->Thankyou();
    }
    virtual void Pass(TurnstileFSM* t)
    {
        t->SetState(&lockedState);
        t->Lock();
    }
};

LockedState TurnstileState::lockedState;
UnlockedState TurnstileState::unlockedState;

Answer 1

问题是，当您尝试在 LockedState::Coin() 内部调用 SetState() 时，类 UnlockedState 是一个 不完整类型：已声明但未定义。 为了修复它，您需要将 Coin() 的定义移至 UnlockedState 的定义之后：

class LockedState : public TurnstileState
{
public:
    virtual void Coin(TurnstileFSM* t);
    ...
};

class UnlockedState : public TurnstileState
{
    ...
};

void LockedState::Coin(TurnstileFSM* t)
{
    ...
}

Answer 2

这很可能是因为它还不知道 UnlockedState 是 TurnstileState 的子类。 将函数从类内部删除到文件末尾：

class TurnstileFSM {
    void SetState(TurnstileState* s);
};

void TurnstileFSM::SetState(TurnstileState* s) {itsState = s;}

Answer 3

在示例中，生成的代码应包含 tscontext.h，并且 TurnStyle 类是从上下文派生的，应在 *tscontext.h 中将其声明为 < em>class TurnStyleContext

在我的例子中，生成的代码如下所示：

    #include "tscontext.h"   // the header file name for the context class"

    // Forward Declarations

    class TurnStyle;

    //----------------------------------------------
    // TurnStyleState: The base state class
    //----------------------------------------------
    class TurnStyleState
    {
      public: 
        virtual const char* StateName() const = 0;
        virtual void Coin( TurnStyle& );
        virtual void Pass( TurnStyle& );
    };

    //----------------------------------------------
    // State: Unlocked
    //----------------------------------------------
    class TurnStyleUnlockedState : public TurnStyleState
    {
      public: 
        virtual const char* StateName() const
            { return "Unlocked"; }
        virtual void Pass( TurnStyle& );
        virtual void Coin( TurnStyle& );
    };
    //----------------------------------------------
    // State: Locked
    //----------------------------------------------
    class TurnStyleLockedState : public TurnStyleState
    {
      public: 
        virtual const char* StateName() const
            { return "Locked"; }
        virtual void Coin( TurnStyle& );
        virtual void Pass( TurnStyle& );
    };
    //----------------------------------------------
    // TurnStyle: The Finite State Machine class
    //----------------------------------------------
    class TurnStyle: public TurnStyleContext
    {
      public: 
        // Static State variables
        static TurnStyleUnlockedState Unlocked;
        static TurnStyleLockedState Locked;

        TurnStyle(); // default Constructor

        // Event functions
        virtual void Coin() { itsState->Coin( *this ); }
        virtual void Pass() { itsState->Pass( *this ); }

        // State Accessor functions
        void SetState( TurnStyleState& theState ) { itsState = &theState; }
        TurnStyleState& GetState() const { return *itsState; }

        const char* GetCurrentStateName() const { return itsState->StateName(); }
        const char* GetVersion() const;

      private: 
        TurnStyleState* itsState;
    };

状态机以这种方式定义：

Context TurnStyleContext     // the name of the context class
FSMName TurnStyle            // the name of the FSM to create
Initial Locked               // the name of the initial state
                             // for C++ output
pragma Header  tscontext.h"   // the header file name for the context class, note the necessary "
{
    Locked
    {
        Coin     Unlocked    Unlock
        Pass     Locked      Alarm
    }
    Unlocked <BeforeUnlocked >AfterUnlocked
    {
        Coin    Unlocked    Thankyou
        Pass    Locked      Lock
    }
}

上下文实现FSMError、Thankyou、Lock、Alarm、Unlock、BeforeUnlocked、AfterUnlocked