在向量C ++中存储类

Question

I am creating a game in C++/DirectX and I have came across a problem of storing sprites. Currently I can create a sprite and then store it in a vector, doing this for one sprite works perfectly. But, when I go to insert another sprite, the texture property of the previous sprite gets deleted. I shall include some screen shots of breakpointing and some code.

The problem that I suspect is that the object is not being placed into the vector and is relying on the temporary object that is used to create the sprite. Here are some screenshots:

https://www.dropbox.com/s/g5xdlaqf35w6q57/1.png

https://www.dropbox.com/s/xmcyv611nqc27xc/2.png

And some code:

// d2World.h
class d2World
{
public:
    // Some functions
    vector<d2Sprite> spritesList;
    // More stuff

private:
    d2Sprite *tempSprite;
    // Other private variables
};

// d2World.h
// Some other functions

// A new object is created by re-assigning it
tempSprite = new d2Sprite();

// When a the sprite is completed, add it to the vector
spritesList.push_back(*tempSprite);

// More stuff here

What I don't understand is why is it only the texture property being affected?

Thanks for your help.

EDIT: Here is the header code for the d2Sprite class:

class d2Sprite
{
public:
    d2Sprite(void);
    ~d2Sprite(void);
    void Load(LPDIRECT3DTEXTURE9 tex);
    void Position(int x, int y);

    int x, y, frame, frameW, frameH, columns;
    float Rotation;

    D3DXVECTOR3 GetPosition();

    D3DXVECTOR2 Scale;
    D3DXVECTOR2 Center;
    D3DXVECTOR2 Translation;

    LPDIRECT3DTEXTURE9 texture;

    D3DCOLOR colour;
};

Answer 1

You are creating a copy of d2Sprite, and LPDIRECT3DTEXTURE9 seems to be a pointer...

spritesList.push_back(*tempSprite);

Why are you creating d2Sprite with new, and then copying them to the vector, you probably should have a

vector<d2Sprite*> spritesList;

and copy the pointer to the vector

spritesList.push_back(tempSprite);

Then call delete on the items in the vector when you don't need them anymore.

Answer 2

Without seeing the full definition of d2Sprite , I can only guess that the reason the texture property is being affected is that d2Sprite either doesn't have a correct copy constructor, or doesn't have a copy constructor at all, and the default copy constructor provided by the compiler doesn't do the right thing to copy the texture property correctly.

When you insert an object into an STL container, it actually inserts a copy of the object, not the object itself. If you don't want copies, consider making the container hold pointers to the objects (so that only the pointer itself is copied, not the object).

Answer 3

This is only a guess, since there isn't enough code shown to know for sure. Here is what I think is happening:

d2Sprite has no copy constructor, and the vector contains d2Sprite objects, not pointers. When the temporary object tempSprite is added to the vector, it is copied, so the raw pointer LPDIRECT3DTEXTURE9 is copied bit-for-bit.

I am going to guess here that you are deleting or overwriting the temporary object tempSprite. When the temporary is deleted or overwritten, the d2Sprite in the vector now has a LPDIRECT3DTEXTURE9 that points to freed memory. This will cause the texture to be lost. Note that it may keep displaying correctly until the memory gets overwritten, usually when the next memory allocation is done. When the next d2Sprite is created, memory will be allocated, and your (already freed) DIRECT3DTEXTURE9 object will likely be overwritten at that time.

Generally speaking, issues like this can be avoided if you use RAII, specifically smart pointers like boost::shared_ptr or (in C++ 11) std::shared_ptr. Used properly, RAII takes care of these kinds of allocated memory lifetime problems. Without RAII, you must track the lifetime of all allocated resources.