C ++ / SDL：矢量/表面问题

Question

Here is the newest problem I am running into. I have a class called Projectiles which holds the basic makeup of a projectile. It's coordinates, and the image which it uses. Here is the basic structure:

class Projectile
{
    private:
        void load();

    public:
        SDL_Surface *surface;
        SDL_Surface* returnSurface()
        {
            return surface;
        }

        Projectile( int );
        void coordinates( int, int );

        int type;
        int width, height;

        int positionX, positionY;

        bool alive;
};

Projectile::Projectile( int type )
{
    type = 1;
    alive = true;
    width  = 83;
    height = 46;
}

void Projectile::load()
{
    SDL_Surface* loadedImage = NULL;

    loadedImage = IMG_Load( "hero.png" );
    surface = SDL_DisplayFormat( loadedImage );

    SDL_FreeSurface( loadedImage );
}

void Projectile::coordinates( int x, int y )
{
    positionX = x;
    positionY = y;
}

Now, I also have my hero class which holds the projectile objects in a vector like such:

vector< Projectile > projectiles;

I have a method in the hero class which makes a new projectile and pushes it into this vector like so:

void Hero::newProjectile( int type )
{
    projectiles.push_back( Projectile( type ) );
    projectileCount++;
}

and then a draw method which is called at the very end of my main loop which does the following:

void Hero::drawProjectileState( SDL_Surface* destination )
{   
    for( int i = 0; i < projectileCount; i++ )
    {
        SDL_Rect offset;
        offset.x = positionX;
        offset.y = positionY;
        SDL_BlitSurface( projectiles[i].returnSurface(), NULL, destination, &offset );
    }
}

conceptually, I thought this would work just fine. Originally my projectile class held ALL of the projectiles coordinates in its own vector, but I came across a problem when I wanted to delete them. Since they all used the same surface resource, deleting one while another was on the screen would cause the game to crash. I thought this would solve the problem ( each having their own surface resource ), but I am getting

Access violation reading location 0xccccccf8.

when it attempts to draw the projectile at :

SDL_BlitSurface( projectiles[i].returnSurface(), NULL, destination, &offset );

I have a feeling i am misunderstanding the way the surface referencing works. What would be the best way to give each projectile its own surface, so that I can delete them independently?

edit: just to clear up possible confusion, I want to be able to FREE the surfaces independently. Freeing a surface once one projectile dies, but another was still on the screen is what was causing the crashes initially.

Answer 1

Projectile::Projectile( int type )
{
    type = 1;
    alive = true;
    width  = 83;
    height = 46;
}

void Hero::newProjectile( int type )
{
    projectiles.push_back( Projectile( type ) );
    projectileCount++;
}

In the code above, you never loaded a surface. You never even initialized surface , so it's pointing off in space, hence the access violation in drawProjectileState when you do this:

SDL_BlitSurface( projectiles[i].returnSurface(), NULL, destination, &offset );