Cannot compile FSM sample code - c++

Question

There is a nice state machine tutorial called UML Tutorial: Finite State Machines by Robert C. Martin. But I can't compile the sample code it provides. I got *FsmTest.cpp(46) : error C2664: 'SetState' : cannot convert parameter 1 from 'class UnlockedState *' to 'class TurnstileState '
Please, help. Thanks.
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

The problem is that when you try to call SetState() inside of LockedState::Coin(), the class UnlockedState is an incomplete type: it has been declared but not defined. In order to fix it, you'll need to move the definition of of Coin() to after that of UnlockedState:
class LockedState : public TurnstileState
{
public:
virtual void Coin(TurnstileFSM* t);
...
};
class UnlockedState : public TurnstileState
{
...
};
void LockedState::Coin(TurnstileFSM* t)
{
...
}

Answer 2

Most likely this is because it does not know UnlockedState is a subclass of TurnstileState yet. Remove the function from inside the class to the end of the file:
class TurnstileFSM {
void SetState(TurnstileState* s);
};
void TurnstileFSM::SetState(TurnstileState* s) {itsState = s;}

Answer 3

In the example, the generated code should include the tscontext.h, and the TurnStyle class is derived from the context, which should be declared in *tscontext.h" as class TurnStyleContext.
In my case the generated code looks like this:
#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;
};
with the state machine defined this way:
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
}
}
The context implements FSMError, Thankyou, Lock, Alarm, Unlock, BeforeUnlocked, AfterUnlocked