Question

Possible Duplicate:
C++: Delete this?

I am trying to create a system to manage states for a game.

The issue with my current design is that when I switch states, the old state is deleted before control switches over to the new state.

The following is a simplified version of my code:

class StateManager;

class State
{
public:
    virtual void update(StateManager &manager)= 0;
    virtual ~State(){}
};


class StateManager
{
public:
    void setState(std::unique_ptr<State> && newState )
    {
        currentState = std::move(newState);
    }
    std::unique_ptr<State> currentState;

    void run()
    {
        currentState->update(*this);
    }
};

Notice how if a State object calls StateManager::setState while in the update method, there will be a period of time when a member function is being called on an object that has just been destroyed.

A complete example of this behavior is at http://ideone.com/WHLzJL. Note how the destructor for FirstState is called before FirstState::update returns.

Is this undefined behavior in C++?
If so, how should I change my design?

Answer 1

No, it’s okay, if you are careful: https://isocpp.org/wiki/faq/freestore-mgmt#delete-this