c++ - 无法从数组或指针 vector 内部访问指向对象的成员

Question

好的，我有一个指向对象类 GameObject 的指针 vector (也尝试过一个数组)-

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

并成功地用指向 GameObject 派生类的对象的指针填充它
( map 对象和玩家角色)

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

但是，非常奇怪的是，我似乎无法访问所指向的任何对象的任何成员
通过 vector/数组中的任何指针，即使我已经验证它们在那里。对于
为了调试我有:

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  

所以一旦指针被存储在vector中，它似乎就知道它是什么了，
但不是它的任何成员......有什么想法吗？我似乎无法理解一个宇宙
这个逻辑可以存在的地方......

类定义:

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;

   }
}

};

谢谢，非常感谢您的帮助和时间!

Answer 1

您有一个基类 GameObject，它具有实例变量 Pos_x、Pos_y 等。然后您将其子类化为 MapObject、PlayerObject，它们具有自己的同名实例变量。这导致每个派生类都有两个这样的变量——(一个用于基础，站点用于派生)。

然后您可以通过指向 GameObject* 的指针访问这些变量，这将只提供对基类实例变量的访问。如您的测试所示，这些不包含您期望的值。

您不需要在基类和子类中都声明这些实例变量。在这种情况下，单独的变量看起来并没有起到任何作用；相反，它会阻止您的代码工作。定义的类应该只在基类中的那些之上定义额外的字段。