A question on Pointers.

[sundar0206]

I am not pretty sure if I should post this here.

Well another query for the day. A bit long post this time. Please bear with me and help me

I have a class called TEnt which basically defines a entity.
I have another class called Manager which sort of manages the entity. The manager is a singleton class which has the following members

        /*! This is called from other classes to register the instance with the manager*/
        void REGISTER_ENTITY_INSTANCE(TEnt& instance);

        /*! Call the set entity call in each of the registered entities*/
        void EntityCall(void);
        /*! Calls a draw entity call to each of the registerdd entity*/
        void drawEntities(void);
        /*! Prints out a test message*/
        void print();

    private:
        /*! A vector of TEnts*/
        std::vector < TEnt* >  m_ppTEntList;


    ///////////////////////////////////////////converting this into a singleton
    ////////////////////////////////////////////////////////////////////////////
     private:
            EntityManager(){;}
            EntityManager(const EntityManager&){;}
            EntityManager& operator= (const EntityManager&){;}
            static EntityManager* m_pInstance;
            static bool is_InstanceSet;

        public:
            static EntityManager* getPInstance();
            ~EntityManager()
            {
                 is_InstanceSet=false;
             }

I have a Screen class which displays all the entities on the screen and a LevelEditor class which initialises and registers the entities on to the entity manager.

My Level Editor Class has the following function

void LevelEditor::Init_Level(){
EntityManager* Manager=EntityManager::getPInstance();
Manager->REGISTER_ENTITY_INSTANCE(a);
}

The REGISTER_ENTITY_INSTANCE(a) pushes the address of the instance onto a vector.

m_ppTEntList.push_back(&instance);

and my screen class has this

//Init level
LevelEditor* Levels=new LevelEditor;
Levels->Init_Level();
//Init the Emanager
EntityManager* EManager=EntityManager::getPInstance();

This piece of code initialises the level and gets a instance of the Manager.

Now This is the error I am facing
When I call the print function in the screen class it works fine .
it says that a entity has been registered and that the size of the vector is now 1. But this is the piece of code that seems to go wrong and creates a SEGMENTATION fault.

  vector<TEnt*>::iterator iter;
    for (iter=m_ppTEntList.begin();iter!=m_ppTEntList.end();iter++)
    {
            (*iter)->my_entity_paint();
    }

All I wanted to do was access every element of the vector and then call a function of each of the element.

Can any one point me to where I am wrong or any better way at all to how this can be done.

[ZuK]

The REGISTER_ENTITY_INSTANCE(a) pushes the address of the instance onto a vector.

m_ppTEntList.push_back(&instance);

Just guessing here. Are you shure instance doesn't go out of scope after that.
Kurt

[sundar0206]

I am not exactly sure as to what you mean by going out of scope!!
But it seems to register it because when I test the size of the vector from the screen class I dont get a error and it says the entity has been properly registerd

[ZuK]

i was referring to sth like this

void createInstance() {
     entity a;
     REGISTER_ENTITY_INSTANCE(a);
}

In such a case the entity a would go out of scope after return from createInstance() and you would have added a dangling pointer to the vector.
Kurt

[sundar0206]

I seem to have gone wrong with the pointing but I think what you said is probably the cause of the problem.

This is from a a level editor class that I use to register the entities on to the manager.

void LevelManager::InitLevel(){
    //A Instance of Entitymanager to which all the instances are registered
    vec3d pos;
    pos.Initialize(10,0,0);
    TEnt a(pos);
    EntityManager* Manager=EntityManager::getPInstance();
    Manager->REGISTER_ENTITY_INSTANCE(a);
}

and this is from the screen class

    LevelEditor* Levels=new LevelEditor;
    Levels->Init_Level();
    EntityManager* EManager=EntityManager::getPInstance();
    EManager->drawEntities();

The above code throws up errors and causes segmentation faults.

But if i totally take off the level editor and put everything into the screen class like

EntityManager* EManager=EntityManager::getPInstance();
vec3d pos;
pos.Initialize(3,0,3);
TEnt a(pos);
EManager->REGISTER_ENTITY_INSTANCE(a);
EManager->drawEntities();

This doesn't......

Is this due to the error which was told in the last post


But I want to have a seperate Level Editor class which I can integrate with a GUI.

[ZuK]

You will have to dynamically create the TEnt in InitLevel().
If you would use a vector of smart pointers to register the entities you don't have to worry to delete the entities.
Kurt

[sundar0206]

Can you please give me a example of as to how I should be doing it?

[ZuK]

void LevelManager::InitLevel(){
    //A Instance of Entitymanager to which all the instances are registered
    vec3d pos;
    pos.Initialize(10,0,0);
    TEnt * a = new TEnt(pos);
    EntityManager* Manager=EntityManager::getPInstance();
    Manager->REGISTER_ENTITY_INSTANCE(a);
    // REGISTER_ENTITY_INSTANCE should take a TEnt *
}

Kurt

[sundar0206]

Thanks a lot Kurt...

Works great now )

Is it fine if I ask you some thing else??

This is another problem I have.
I got a following inheritance hierarchy.

TEnt, Male and Female inherits from a baseentity.
What I want is my Entity Manager class to access all the instances of all the three types of entities.
Currently I have a vector of pointers to each of the individual entities which i register in the register function

std::vector < TEnt* >  m_ppTEntList
void REGISTER_ENTITY_INSTANCE(TEnt* instance);

This would mean that I would have to declare a vector one for each of the child classes and if I increase the class count I would propotionally keep increasing. Also the register and any other function that takes in a input needs to be repeated.

I know this part is bad coding

Can this be avoided?

[potatoCode]

you can use a pointer to the base class to access the derived.

std::vector<baseentity*> bvec;