Graphics *Graphics::instance;

to the top of my Graphics.cpp file. This did the trick and thankfully got rid of the linker error.

Error	1	error LNK2001: unresolved external symbol "protected: static class Graphics * Graphics::instance" (?instance@Graphics@@1PAV1@A)	Graphics.obj

I am doing the following in main:

Graphics *rhGraphics = new Graphics();
 
rhGraphics->setInstance(rhGraphics);

Not sure where else it could be causing problems. My codes has gotten quite large, as I wasn’t doing oop when I first started the project. If you need more than just this, please let me know. This problem’s been bugging me for too long…

Following one of my previous comments you need to do the following in a “main program” where you create the cgvDraw object.

1. Create the object
2. Pass in the object’s instance to it’s static instance variable.

cgvDraw cgObject = new cgvDraw();
cgObject->setInstance(cgObject);

Looking at your code and it is a really good idea.

I am having a few problems however in getting it to work.. It may be a general C++ error but for some reason it keeps complaining that the instance variable isn’t defined..

class cgvDrawWrap
{
	protected:
		static cgvDrawWrap *instance;
 
	public:
		static void drawSceneWrap()
		{
			instance->drawScene();
		}
 
		static void setInstance(cgvDrawWrap *in)
		{
			//printf("\nBefore %ld\t%ld", in, cgvDrawinstance);
			instance = in;
			//printf("\nAfter %ld\t%ld", in, instance);
		}
};
 
class cgvDraw : public cgvDrawWrap
{
	public:
 
		// Class constructor
		cgvDraw()
		{
			// Set the instance of the class
			this->setInstance(this);
                        ..........................
                }
};

this is only a cut down version of the offending code – but it seems the same as what you have and I don’t know why it isn’t working.

Any ideas would be amazing.

“undefined reference to `cgvDrawWrap::instance’”

Regards,
Richard

http://www.parashift.com/c++-faq-lite/pointers-to-members.html#faq-33.2
“Note: static member functions do not require an actual object to be invoked, so pointers-to-static-member-functions are usually type-compatible with regular pointers-to-functions. However, although it probably works on most compilers, it actually would have to be an extern “C” non-member function to be correct, since “C linkage” doesn’t only cover things like name mangling, but also calling conventions, which might be different between C and C++.”

Do you have any snippets of code?

I tried something similar but my program crashes on startup. When running the debugger, I find that when I set my instance, the vfptr is set correctly, but when I’m inside the delegating function (the one actually called by glut) the vfptr is 0×0. So, basically, mine works with non-virtual methods, but not with virtual methods.

I’m using Visual Studio 2008. Any suggestions?
– Seth

I have a function in my AnimationFramework.h

static void setInstance(AnimationFramework * framework);

AnimationFramework.cpp

void AnimationFramework::setInstance(AnimationFramework *framework) {
	instance = framework;
}

The main.cpp looks something like this:

int main(int argc, char *argv[]) {
 
	AnimationFramework *f = new KeyFrameFramework(); // Subclass of AnimationFramework
	f->setInstance(f);
	f->setTitle("Key Framing:");
	f->setLookAt(0.0, 2.0, 10.0, 0.0, 2.0, 0.0, 0.0, 1.0, 0.0);
	f->startFramework(argc, argv);
	return 0;
}