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Access Violation...

Started by elendil67 Aug 5, 2002 at 10:15 PM 11 replies 900+ views

Original Post

Aug 5, 2002 at 10:15 PM

Hey all, I''m not totally sure whether this should go in the DirectX or OpenGL forum (I''m making a mini-engine for both API''s), so moderators please feel free to move it. In my FinishScene() function, if the current renderer is Direct3D, I simply call the EndScene() and Present() functions. If my renderer is OpenGL, I simply call SwapBuffers(), with my device context as a parameter. Simple enough. If I run the function in Direct3D, it works flawlessly. If I run it in OpenGL though, I encounter some problems. I get an Access Violation error, and the debugger traces me back to the EndScene() function. The only thing is that if I''m using OpenGL, the if statement should skip the code... but I get an Access Violation. If you''re confused, here''s the source:

  
// Function to finish rendering the scene

int CEngine::FinishScene()
{
	// If Direct3D is the current renderer

	if(this->m_bOpenGL == false)
	{
		// Finish rendering the scene in Direct3D


		// Finish rendering the scene

		this->m_pDirect3DDevice->EndScene();

		// Present the scene

		this->m_pDirect3DDevice->Present(NULL, NULL, NULL, NULL);
	}

	// If OpenGL is the current renderer

	else
	{
		// Finish rendering the scene in OpenGL


		// Swap buffers

		SwapBuffers(this->m_hDC);
	}

	return 1;
}

I''m not sure whether I''m using the debugger right (in that function... I run Go but it stops at EndScene()), because this is one really weird error. .elendil67

Just3D

Aug 5, 2002 at 10:27 PM

I''m wondering if the this statements are necessary. You are already in the scope of the class, therefore you can omit all of the this-> words. In my experience, if there is a pointer that you can avoid dealing with, do so.

I''m not positive this is the prblem, but its a start.

Hope this helps!

"There are only three types of people in this world: those who can count, and those who can''t."

Just3D
Justin Nordin
J Squared Productions
www.jsquaredproductions.com

elendil67

Aug 5, 2002 at 10:58 PM

Well... I just like using this

. It lets me know which are global variables, which are local variables... etc. I don''t think that would be the problem.

.elendil67

Arild Fines

Aug 5, 2002 at 11:00 PM

The this-> is an acceptable idiom - it stresses that you are accessing member variables instead of locals or globals. It does seem a bit redundant though when you are already using the m_ thingie.
I''m more concerned about the if ( this->m_bOpenGL == false ) statement. These kinds of conditionals just cry out for polymorphism instead. I assume you have similar conditionals in the rest of your engine''s methods as well?
Anyway - the code DOES look correct - I would venture to guess that your problem really cannot be found in this block alone.

"Imagine the people who believe such things and who are not ashamed to ignore, totally, all the patient findings of thinking minds through all the centuries since the Bible was written. And it is these ignorant people, the most uneducated, the most unimaginative, the most unthinking among us, who would make themselves the guides and leaders of us all; who would force their feeble and childish beliefs on us; who would invade our schools and libraries and homes."
Isaac Asimov

elendil67

Aug 5, 2002 at 11:11 PM

Well... that''s what I was thinking of doing. I am about to rip apart the code

.

.elendil67

elendil67

Aug 6, 2002 at 11:59 AM

Thanks for that info, everybody. I''ve made my engine more polymorphic, so it''s something like this

  
class CGraphics
{
public:
	
	// Function to initialize the engine

	virtual int Create(HWND hwnd, HDC hdc, int width, int height, int bpp);
	
	// Function to set the clear color of the screen

	virtual int SetClearColor(unsigned char r, unsigned char g, unsigned char b);

	// Function to begin rendering the scene

	virtual int BeginScene();

	// Function to finish rendering the scene

	virtual int EndScene();
	
protected:
	ofstream          m_fLog;											// Log file

};

class COpenGL : public CGraphics
{
public:
	// Constructor

	COpenGL();

	// Destructor

	~COpenGL();

	// Function to initialize the engine

	int Create(HWND hwnd, HDC hdc, int width, int height, int bpp);
	
	// Function to set the clear color of the screen

	int SetClearColor(unsigned char r, unsigned char g, unsigned char b);
	
	// Function to begin rendering the scene

	int BeginScene();
	
	// Function to finish rendering the scene

	int EndScene();
	
private:
	HGLRC    m_hGLRC;												// Handle to the OpenGL rendering context

	HDC		 m_hDC;													// Handle to the device context

};

I don''t think I need to show you CDirect3D too, because that''s pretty much the same as COpenGL with differences in the members. But, when I compile it, I get errors like:


CDirect3D.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::EndScene(void)" (?EndScene@CGraphics@@UAEHXZ)
COpenGL.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::EndScene(void)" (?EndScene@CGraphics@@UAEHXZ)
test.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::EndScene(void)" (?EndScene@CGraphics@@UAEHXZ)
CDirect3D.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::BeginScene(void)" (?BeginScene@CGraphics@@UAEHXZ)
COpenGL.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::BeginScene(void)" (?BeginScene@CGraphics@@UAEHXZ)
test.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::BeginScene(void)" (?BeginScene@CGraphics@@UAEHXZ)
CDirect3D.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::SetClearColor(unsigned char,unsigned char,unsigned char)" (?SetClearColor@CGraphics@@UAEHEEE@Z)
COpenGL.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::SetClearColor(unsigned char,unsigned char,unsigned char)" (?SetClearColor@CGraphics@@UAEHEEE@Z)
test.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::SetClearColor(unsigned char,unsigned char,unsigned char)" (?SetClearColor@CGraphics@@UAEHEEE@Z)
CDirect3D.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::Create(struct HWND__ *,struct HDC__ *,int,int,int)" (?Create@CGraphics@@UAEHPAUHWND__@@PAUHDC__@@HHH@Z)
COpenGL.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::Create(struct HWND__ *,struct HDC__ *,int,int,int)" (?Create@CGraphics@@UAEHPAUHWND__@@PAUHDC__@@HHH@Z)
test.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall CGraphics::Create(struct HWND__ *,struct HDC__ *,int,int,int)" (?Create@CGraphics@@UAEHPAUHWND__@@PAUHDC__@@HHH@Z)
Debug/Engine 02.exe : fatal error LNK1120: 4 unresolved externals

.elendil67

Arild Fines

Aug 6, 2002 at 1:26 PM

Either provide an implementation(possibly empty) for the virtuals in your base class, or make them pure virtual.

Either:


virtual int Create(HWND hwnd, HDC hdc, int width, int height, int bpp)
{ /*some code here*/;}

or:


virtual int Create(HWND hwnd, HDC hdc, int width, int height, int bpp) = 0;

elendil67

Aug 6, 2002 at 1:52 PM

Thanks Arild Fines, it works now! I can''t really make them pure virtual functions, because you can''t make objects of an abstract class. But the empty braces worked! Thanks!

.elendil67

Evil Bill

Aug 6, 2002 at 2:47 PM

quote:
Original post by elendil67
I can''t really make them pure virtual functions, because you can''t make objects of an abstract class.

  
class CGraphics
{
public:
   virtual void Draw() = 0;
};

class CD3D : public CGraphics
{
public:
   virtual void Draw() {/* Code Here */}
};

void Render(CGraphics* pGfx)
{
   pGfx->Draw();
}

int WinMain(...)
{
CGraphics* pGfx = new CD3D;

   Render(pGfx);
}

Thats a better way to do it IMO.

Steve
DirectX Programmer
Soon to be the new Bill Gates

Arild Fines

Aug 6, 2002 at 5:22 PM

quote:
Original post by elendil67
I can''t really make them pure virtual functions, because you can''t make objects of an abstract class.

Thats sort of the idea of abstract classes. You dont make instances of them, you make instances of the derived classes. Why would you ever need an instance of a CGraphics object?

elendil67

Aug 6, 2002 at 5:55 PM

Hermmm... you''re right. I was thinking of CGraphics to be more of an interface. Well, since it''s a module, I guess I''ll just have a pointer to it in the engine class... so it will work! Thanks

.elendil67

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