无法从内部数组或指针向量中访问尖头对象的成员

Question

OK, I have a vector (have also tried an array) of pointers to objects class GameObject-

//GameObject* objPriority_vec [oc+1];
std::vector<GameObject*> objPriority_vec(oc+1);

and have successfully filled it with pointers to objects of derived classes of GameObject
(MapObject and PlayerCharacter)

for(int o_r = 1; o_r <= oc; o_r++)
{
    std::string render_ref = CurrentArea->ObjectRef[o_r];          
    MapObject* render_obj = CurrentArea->ObjectMap[render_ref];

    objPriority_vec[o_r] = render_obj;

}
objPriority_vec[0] = Player_1;    // Player_1 is a pointer to obj   
                                  // PlayerCharacter

But, very strangely, I cannot seem to access any of the members of any of the objects pointed to
by any of the pointers in the vector/array, even though I have verified that they are in there. For
sake of debugging I have:

GameObject* prioritycheck = objPriority_vec[0];  //has been explicitly declared
                                                 //as Player_1 

//When tried one a time  

if( prioritycheck == Player_1 ) gameRunning = false;      //  returns false 
                                                          //(when it should)
if( Player_1->Pos_y > 500) gameRunning = false;           //  returns false 
if( objPriority_vec[0]->Pos_y > 500) gameRunning = false; //  does not 
if( prioritycheck->Pos_y > 500) gameRunning = false;      //  does not  

So once the pointer has been stored in the vector, it seems to know what it is,
but not what any of its members are... any ideas? I can't seem to comprehend a universe
where this logic can exist...

Class Definitions:

class GameObject

{
public:
std::string Graphic_path;
int height;
int width;
int Pos_x;
int Pos_y;
int Vel;
m_dir Dir;
bool moving;
bool colliding;
CollisionBox cCollisionBox;

virtual void Move(){}
virtual void Show(SDL_Surface*, SDL_Surface*){}
virtual void Add(){}
GameObject() {Graphic_path = "NULL"; Pos_x = 0; Pos_y = 0; height = 0; width = 0;}
}; 



class MapObject : public GameObject
{
public:
SDL_Surface* Graphic;
std::string Graphic_path;
int height;
int width;
int Pos_x;
int Pos_y;
int Vel;
m_dir Dir;
bool moving;
bool colliding;
CollisionBox cCollisionBox;


bool SetCollisionBox(int x, int y, int w, int h)
{
cCollisionBox.h = h;
cCollisionBox.w = w;
cCollisionBox.x_off = x;
cCollisionBox.y_off = y;


}
bool CheckCollide(){return false;}


void HandleCollide (int vel_x, int vel_y, int vel, m_dir dir)
{
 switch (dir)
 {

    case Up:
    break;

    case Down:
    break;

    case Left:
    break;

    case Right:
    break;

 }
}

virtual void Move(int v, m_dir dir)
{

 switch (dir)
 {
   case Up:
        Pos_y -= v;
        break;

   case Down:
        Pos_y += v;
        break; 

   case Left:
        Pos_x -= v;
        break;

   case Right:
        Pos_x += v;
        break;     
  }


}

void StandStill()
{
 Vel = 0;
 moving = false;
}



virtual void Show(SDL_Surface*, SDL_Surface*){}
virtual void Add(){}


MapObject()
{
Graphic = NULL; Graphic_path = "NULL"; 
Pos_x = 0; Pos_y = 0; 
height = 0; width = 0;
colliding = false; moving = false;

}


};


class PlayerCharacter : public GameObject
{
public:
int Pos_x;
int Pos_y;
int Vel;
int Vel_x;
int Vel_y;
int frame;
int frame_count;
m_dir Dir;
bool moving;
bool colliding;
SDL_Rect CharClip[20];
CollisionBox cCollisionBox;
void SetClip_Walk()
{
int CharWidth = 22;
int CharHeight = 45;
int CharGap = 6;



    for (int z = 0; z <= 19; z++)
    {
        CharClip[ z ].x = (z * CharWidth) + (z * CharGap);
        CharClip[ z ].y = 0;
        CharClip[ z ].w = CharWidth;
        CharClip[ z ].h = CharHeight;
    }



}

PlayerCharacter()
{
             Pos_x = 0; Pos_y = 0; Vel_x = 0; Vel_y = 0; 
             Vel = 0; moving = false; colliding = false; 
             frame = 0; frame_count = 0;
             Dir = Down;
             SetClip_Walk();
}

bool SetCollisionBox(int x, int y, int w, int h)
{
cCollisionBox.h = h;
cCollisionBox.w = w;
cCollisionBox.x_off = x;
cCollisionBox.y_off = y; 
}

void HandleCollide ()
{

   Pos_y -= (Vel_y);
   Pos_x -= (Vel_x);


   cCollisionBox.x = Pos_x + cCollisionBox.x_off;
   cCollisionBox.y = Pos_y + cCollisionBox.y_off;


}



void Move(int v_x, int v_y, int v, m_dir dir)
{



switch (dir)
{
   case Up:

        Pos_y += v_y;

        break;

   case Down:
        Pos_y += v_y;

        break; 

   case Left:

        Pos_x += v_x;

        break;

   case Right:

        Pos_x += v_x;

        break;     
}


cCollisionBox.x = Pos_x + cCollisionBox.x_off;
cCollisionBox.y = Pos_y + cCollisionBox.y_off;


}

void StandStill()
{
 Vel = 0; Vel_x = 0; Vel_y = 0;
 moving = false;
 colliding = false;
}

void Show(SDL_Surface* source, SDL_Surface* dest)
{

   if (Vel != 0) frame_count++;
   if (frame_count > 3) {frame++; frame_count = 0;}
   if (frame > 4) frame = 1;

   if (Vel == 0) {frame = 0; frame_count = 0;}


   switch (Dir)
   {
          case Up: 
          ApplySurface (Pos_x, Pos_y, source, OutputScreen, &CharClip[frame]);
          break;

          case Down:
          ApplySurface (Pos_x, Pos_y, source, OutputScreen, &CharClip[frame+5]);
          break;

          case Left:
          ApplySurface (Pos_x, Pos_y, source, OutputScreen, &CharClip[frame+10]);
          break;

          case Right:
          ApplySurface (Pos_x, Pos_y, source, OutputScreen, &CharClip[frame+15]);
          break;

   }
}

};

Thank you, all your help and time is greatly appreciated!

Answer 1

You have a base class GameObject which has instance variables Pos_x, Pos_y, etc. You have then subclassed this with MapObject, PlayerObject which have their own instance variables of the same name. This results in each of the derived classes having two of these variables - (one for the base, site for the derived).

You then access these via a pointer to GameObject* which will only provide access to the base class instance variables. As your tests show these do not contain the values you are expecting.

You do not need to declare these instance variables in both base and subclasses. It does not look like having separate variables is serving any purpose in this case; rather it is stopping your code from working. The defined class should only define additional fields on top of those in the base class.

Answer 2

"If you want to compare arbitrary class hierarchies, the safe bet is to make them polymorphic and use dynamic_cast."

See https://stackoverflow.com/a/5662867/912757

Answer 3

try to change for example this statement

if( prioritycheck == Player_1 ) gameRunning = false;

to

if( dynamic_cast<PlayerCharacter *>( prioritycheck ) == Player_1 )  gameRunning = false;