Unhandled exception in font render function C++ SDL

Question

I'm working on a PONG clone and just on the title screen. I have a class to work the title screen loop of the state machine and it uses very little, only a single sprite and a single true type font message. But when I call the function to render the message onto the SDL_Surface, it throws my program into whack. The error I receive is Unhandled exception at 0x6F4C2A9D (SDL_ttf.dll) in Pong.exe: 0xC0000005: Access violation reading location 0x00000000. Usually this means that I didn't initialize something or didn't define it in the class definition or something, but it all seems in order. So I'll post the code here in hopes that someone sees what's up with the render function or the bits surrounding it.

To be perfectly clear the exception is thrown on this line:

Title_Message = TTF_RenderText_Solid(font, "PONG", color);

//start code
/*CLASSES*/

class GameState
{
public:
    virtual void events() = 0;
    virtual void logic() = 0;
    virtual void render() = 0;
    virtual ~GameState(){};
};

class Button
{
public:
    SDL_Rect button_clip[2];
    SDL_Rect button;
    SDL_Surface *button_sprite = NULL;
    Button();
};

class Title : public GameState
{
private:
    SDL_Surface *Title_Message = NULL;
    SDL_Rect *clip;
    Button Title_Button;
public:
    void events();
    void logic();
    void render();
    Title();
    ~Title();
};

/*FONTS*/
SDL_Color color = { 255, 255, 255 };
TTF_Font *font = NULL;

bool init()
{
    //initialize all SDL subsystems
    if (SDL_Init(SDL_INIT_EVERYTHING) == -1)
    {
        return false;
    }
    //set up screen
    screen = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE);
    //check screen
    if (screen == NULL)
    {
        return false;
    }
    //init TTF
    if (TTF_Init() == -1)
    {
        return false;
    }
    //set window caption
    SDL_WM_SetCaption("PONG", NULL);
    //if evetything worked
    return true;
}

//load files
bool load_files()
{
    font = TTF_OpenFont("PIXELITE.ttf", 45);
    if (font == NULL)
    {
        return false;
    }
    return true;
}

/*CLASS DEFINITIONS*/

Button::Button()
{

}

Title::Title()
{
    Title_Message = TTF_RenderText_Solid(font, "PONG", color);
    Title_Button.button_sprite = load_image("Start.png");
    Title_Button.button.x = 200;
    Title_Button.button.y = 350;
    Title_Button.button.w = 100;
    Title_Button.button.h = 50;
    //clips not hover
    Title_Button.button_clip[0].x = 0;
    Title_Button.button_clip[0].y = 0;
    Title_Button.button_clip[0].w = 100;
    Title_Button.button_clip[0].h = 50;
    //clips hover
    Title_Button.button_clip[1].x = 0;
    Title_Button.button_clip[1].y = 50;
    Title_Button.button_clip[1].w = 100;
    Title_Button.button_clip[1].h = 50;
}

Title::~Title()
{
    SDL_FreeSurface(Title_Message);
    SDL_FreeSurface(Title_Button.button_sprite);
}

void Title::events()
{
    int x = 0;
    int y = 0;
    while (SDL_PollEvent(&event))
    {
        if (event.type == SDL_MOUSEMOTION)
        {
            x = event.motion.x;
            y = event.motion.y;
            if ((x > Title_Button.button.x) && (x < (Title_Button.button.x + Title_Button.button.w)) && (y > Title_Button.button.y) && (y < (Title_Button.button.y + Title_Button.button.h)))
            {
                clip = &Title_Button.button_clip[1];
            }
            else
            {
                clip = &Title_Button.button_clip[0];
            }
        }
        if (event.type == SDL_QUIT)
        {
            quit = true;
        }
    }
}

void Title::logic()
{

}

void Title::render()
{
    apply_surface(Title_Button.button.x, Title_Button.button.y, Title_Button.button_sprite, screen, clip);
    apply_surface((SCREEN_WIDTH - Title_Message->w) / 2, 100, Title_Message, screen);
}

Anybody got an idea? Thanks!

Answer 1

I will post my suggestions from the comments as an actual answer:

The trouble-causing line Title_Message = TTF_RenderText_Solid(font, "PONG", color); refers to the global variable font of type TTF_Font*. The line is also part of the constructor of the class Title.

main looks like this:

int main(int argc, char* args[])
{
    //init SDL
    init();
    //load everything
    load_files();
    currentState = new Title;
    //...

font is initialized to NULL at declaration, an actual object is assigned only in load_files() which is executed at the beginning of main before Title is the first time instantiated.

So load_files() has to assign a valid pointer to font, otherwise the next line in main will cause an access violation.

load_files() provides a return value depending on whether creating and assigning this object was successful. However main never checks for this value and thus it is not guaranteed that font is a valid pointer.

As knefcy pointed out the problem was a wrong filename in load_files().