D3DXVECTOR3 vpos = FindPosition(warehouse, Convert_Truck_ID_To_Name(this->m_truck_id));

The line is contained in the class called Truck,

It needs to retrieve where it's going to park in the warehouse.

In this case, The FindPosition requires a warehouse pointer/handle to

know where to start to look.

I've several options here.

1) Store a global pointer of the warehouse, so I can access it anywhere

2) Use a Singleton to do the similar stuff

3) Store a local pointer, so a warehouse is always passed into the truck object (Not quite modular in this case)

4) Make use of the state machine, and let the state machine store a vector/map of game objects pointers, so it starts to look up from there inside. And I just send a message to the Truck State Machine, the truck state machine fills up the warehouse information and Just put the FindPosition inside the state machine. And it will handle the rest

Should I use option 4? it seems to be the preferred way to go? Not sure, so want to ask your opinion?

Isn't this something that should be handled by your AI/path planning system? I would just place goal points (just a transform) within the warehouse and then assign the goals to the relevant truck(s) at load time and let the A* handle the rest. If you have some kind of AICharacterController for the trucks, it can just be passed one or more goal points that it could go to depending on the current game state. I doubt you want to hard-code the concept of a "warehouse", a warehouse is just a 3D geometry with other semantic data that are used by game objects to perform tasks like going to the correct spot in the warehouse.

Reading it over a few times, especially with the comments about the state machines, I think the question you are trying to ask is:

I've got a game object with it's ID, a truck. And I've got another game object called a warehouse. I want to create an interaction that lets the truck figure out a parking spot in a warehouse. I want to figure out where the truck is supposed to park in the warehouse.

Is that a good restatement?

For your options:

Option 1, a global pointer, does not work well in the general case. Global anything is generally a bad idea in games.

Option 2, a Singleton, is even worse in the general case.

Option 3, a local pointer, is probably close to what you want.

Option 4, "make use of the state machine", gives more information that makes it more clear what you are trying to do.

Based on what I anticipate about your questions, I imagine this:

Have a component or interface, perhaps called IParkingLocation or ParkingLocationComponent

Have your warehouse use that component/interface.

Now in your interaction to park your truck, you can get that interface. Depending on implementation maybe:

ParkingLocationComponent parkingLocation = warehouse->GetComponent( typeid(ParkingLocationComponent) );

or

IParkingLocation parkingLocation = dynamic_cast<IParkingLocation*>(warehouse);

Then you can use a function you build in your interface or component:

position = OutOfWorld;

if( parkingLocation ) {

position = parkingLocation->FindNearestParkingLocation( truck );

}

Your ParkingLocation component or type could have some extra functions to mark the spot as reserved (and also to un-reserve spots), or maybe other functionality as well.

The variables could all be part of your interaction, which seems to be a state machine in your description.

Thanks, buddies, It's all good.

But one thing to mention is, if the truck depends on many other stuff in my game.

Do I have a long parameter list to deal with? It's not the problem of the amount of typing.

The problem is if I extend the number of dependencies in the future, then would that become unmanagable?

Maybe I am wrong, please correct me if I am.

like this.

Truck::Truck(Warehouse* warehouse, Good* goods...)

If I understand you guys' concepts correctly

do it like that?

Truck::Truck(const std::vector<GameObject*>& depends....)

If like phil_t said, completely decoupled?

Maybe just like phil_t said,
 
[code]
D3DXVECTOR3 FindParkingSpot(const std::shared_ptr<GameObject>& pParkingPlace)
{
    D3DMATRIX matPark = pParkPlace->FindFrame("ParkingPlace")->matCombined;
    return D3DXVECTOR3(matPark._41, matPark._42, matPark._43);
}
 
void Parking(const std::shared_ptr<GameObject>& pParkingPlace, const std::shared_ptr<GameObject>& pParkingVehicle)
{
     D3DXVECTOR3 vParkSpot = FindParkingSpot(pParkingPlace);
     pParkingVehcle->setPosition(vParkSpot);
}

Sorry, a couple of typos....

D3DXVECTOR3 FindParkingSpot(const std::shared_ptr<GameObject>& pParkingPlace)
{
    D3DMATRIX matPark = pParkingPlace->FindFrame("ParkingPlace")->matCombined;
    return D3DXVECTOR3(matPark._41, matPark._42, matPark._43);
}
 
void Parking(const std::shared_ptr<GameObject>& pParkingPlace, const std::shared_ptr<GameObject>& pParkingVehicle) const
{
     D3DXVECTOR3 vParkSpot = FindParkingSpot(pParkingPlace);
     pParkingVehcle->setPosition(vParkSpot);
}