Thread: Initializing a class reference inside another class...

I have the following two classes.

Code:

class Surface;
class Sprite;

Surface is just a basic wrapper for some of the SDL functions, and holds clipping information, which is unimportant at the moment.

Sprite contains a reference to Surface.

Code:

class Sprite
{
private:
   Surface& sprite;
   //other members here
public:
  //functions and stuff here
};

Naturally it will not allow me to compile this because it has to initialize sprite(the Surface&).

Code:

1>------ Build started: Project: Project-Varia, Configuration: Debug Win32 ------
1>Compiling...
1>Sprite.cpp
1>c:\documents and settings\raigne\my documents\visual studio 2008\projects\project-varia\project-varia\sprite.cpp(6) : error C2440: 'initializing' : cannot convert from 'int' to 'Surface &'
1>c:\documents and settings\raigne\my documents\visual studio 2008\projects\project-varia\project-varia\sprite.cpp(6) : error C2439: 'Sprite::sprite' : member could not be initialized
1>        c:\documents and settings\raigne\my documents\visual studio 2008\projects\project-varia\project-varia\sprite.h(6) : see declaration of 'Sprite::sprite'
1>Build log was saved at "file://c:\Documents and Settings\Raigne\My Documents\Visual Studio 2008\Projects\Project-Varia\Project-Varia\Debug\BuildLog.htm"
1>Project-Varia - 2 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

It says that it must be done in the initializer list, but I cant figure it out. The full Sprite, and Surface classes are below. I greatly appreciate any insight as to the solution to my predicament.

Code:

#pragma once

class Surface
{
private:
    SDL_Surface* surface;
    std::vector<SDL_Rect> clips;

    bool usable_;
    bool debug_;
public:
    //Constructor
    Surface();
    Surface(const std::string& imagefile);

    //Destructor
    ~Surface();
    
    //Debug
    void SetDebug(bool d) { debug_ = d; };

    //Surface usability function
    const bool& GetUsable() const { return usable_; };

    //Compare rects function
    bool ComRects(const SDL_Rect& a, const SDL_Rect& b);

    //Access the surface
    SDL_Surface* GetSurface();

    //Access rect by ID
    SDL_Rect&    GetClip(const unsigned int& rectID) { if ( rectID <= clips.size() ) { return clips.at(rectID); } };

    //Load a new surface
    bool LoadSurface(const std::string& imagefile);

    //Free surface
    void FreeSurface() { SDL_FreeSurface(surface); };

    //Create a new clip
    void CreateClip(const int& x, const int& y, const int& w, const int& h);

    //Delete a clip
    void DeleteClip(const int& clipID);
};

Code:

#pragma once

class Sprite
{
private:
    Surface& sprite;
    SDL_Rect position;

    std::vector<std::vector<int> > clipbook;
    struct
    {
        short cur_page;
        short cur_clip;
        short start_clip;
        short last_clip;
    };
public:
    Sprite();
    ~Sprite();

    void SetSprite(Surface& surface);
    Surface& GetSprite() { return sprite; };
    
    //clipbook functions
    void AddPage(); //adds a page to the back of the book
    void AddClip(const int& page, const int& clip);//adds a clip to the end of a page
    
    void WarpSprite(const int& x, const int& y);
    void MoveSprite(const int& x_axis, const int& y_axis);

    void AnimateClipPage(const int& page, const int& start_clip = 0);
};

You must initialize references in the initializing section of the constructor:

Code:

class foo
{
private:
	int& m_n;
public:
	foo(int& n) : m_n(n) { }
};

int main()
{
	int n = 0;
	foo a(n);
	return 0;
}

In other words, you can't construct an object and later bind the reference. That's a no-no.
If that's the case, you need to use pointers.

Nope.
References are bound as they are created and remains bound to the same object.
Anything you try to do, including reassigning, will only happen at the object pointed to.
For this, you must use pointers.