c++ - 在类中使用指针时遇到问题

Question

我声明的时候没有任何问题

SDL_Surface *dot = NULL;

全局，但如果 SDL_Surface 对类来说是唯一的，我不能将它设置为 NULL，所以我认为如果我在构造函数中声明它会很好

 dot = load_image( "dot.bmp" );

但我还是得到了一个

Unhandled exception at 0x1002b195 in Uber Mario.exe: 0xC0000005: Access violation reading location 0x0000013c.

在返回 SDL_Surface* 的 load_image 上，有时这恰好是因为图像不好或某个 img 文件类型，所以我尝试了另一个在其他地方可以工作的图像，但它仍然会出现这样的错误。

我认为我只是没有正确使用指针，即使我在学校学习指针并阅读了有关它们的事实，但出于某种原因我总是遇到麻烦。 load_image 返回一个 *SDL_Surface 所以我需要使用一个指针...我想。

这是类:

class Character
{
    private:
    int yVel, xVel;
    int xAcc, yAcc;
    int spd, maxV;

    int JumpPower;

    int FacingRight, FacingLeft;//directing status 0 or 1


    bool Flying, onGround;
    //Type of particle
    SDL_Surface *type;

    public:
    Shine *myShine;
    Animation *walking;
    SDL_Surface *dot;

          //Offsets
    SDL_Rect Rect;

    Character();
    void handle_input();
    void move();
    void show();
    void togglefly();
    void jump();
    void whereami();// check and set various characters statuses
};   



Character::Character()
{
    //Set offsets

    Rect.x = 150;
    Rect.y = 150;
    Rect.w = 20;
    Rect.h = 20;

    yVel = 0;
    xVel = 0;
    yAcc = 0;
    xAcc = 0;

    maxV = 30;
    spd = 2;
    JumpPower = 40;
    Flying = true;

    myShine = new Shine(Rect.x, Rect.y);

//  walking = new Animation("mario.bmp", 3, 0, 0, Rect.w, Rect.h);

            dot = new SDL_Surface();

    dot = load_image( "dot.bmp" );

    myShine->setpos(Rect);
    myShine->setRange(Rect.h*1.5);

}

加载图像函数:

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;

    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;

    //Load the image
    loadedImage = IMG_Load( filename.c_str() );

    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage ); //EXCEPTION OCCURES HERE

        //Free the old surface
        SDL_FreeSurface( loadedImage );

        //If the surface was optimized
        if( optimizedImage != NULL )
        {
            //Color key surface
            SDL_SetColorKey( optimizedImage, SDL_SRCCOLORKEY, SDL_MapRGB( optimizedImage->format, 0, 0xFF, 0xFF ) );
        }
    }

    //Return the optimized surface
    return optimizedImage;

初始化函数

    bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;
    }

    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );

    //If there was an error in setting up the screen
    if( screen == NULL )
    {
        return false;
    }

    //Set the window caption
    SDL_WM_SetCaption( "Particle Test", NULL );

    //Seed random
    srand( SDL_GetTicks() );




    //If everything initialized fine
    return true;
}

Answer 1

顺便说一句，你不是在泄漏执行该代码的资源吗:

dot = new SDL_Surface();
dot = load_image( "dot.bmp" );

执行 load_image 会导致您丢失指向 SDL_Surface() 对象的指针，因此您以后无法删除它。

回答您的主要问题

在使用 SDL_DisplayFormay 之前调用 SDL_Init，它应该可以工作。引自 SDL 文档。

Newbie hint

You have to call SDL_Init before using the SDL_DisplayFormat function. If you don't, your program will crash with an access violation.