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DLL Question

Started by bkt Mar 10, 2004 at 11:44 AM 6 replies 1.2k views

Original Post

Mar 10, 2004 at 11:44 AM

I use the normal method (atleast normal for me) of loading DLL files. That would be loading it through HINSTANCE and then using LoadLibrary and using GetProcAddress to grab a function. I ran into a stall, I need to load classes from DLLs (basically, the whole DLL class structure into my program) as well as anything else within the extern "C++" line. How would I go about doing this without using "GetProcAddress?" I''m currently using extern "C++" __declspec(dllexport) : I know I must include the header file for DLL inclution, but would I need to use __declspec(dllimport) instead? Any help would be great.

bkt

Mar 10, 2004 at 2:41 PM

*bump*

SantaClaws

Mar 10, 2004 at 5:23 PM

The way this is often done with basic DLL functionality is by creating a set of interface functions that you can call that will return an address to the instantiated classes in your DLL process.

So, for instance, you could have a function called "Initialize" in your DLL. When you loaded the DLL, you would GetProcAddress on that and call the Initialize function. The initialize function could return something like the following:

struct exportedData_t
{
    class1_t *class1;
    class2_t *class2;
    // etc
};

You'd allocate and set the values of that structure in the DLL, the return it to the host to do what it pleases with it.

[edited by - SantaClaws on March 10, 2004 6:23:48 PM]

bkt

Mar 10, 2004 at 8:16 PM

I was scrolling through some of the previous topics on this, someone suggested using a "pluggable factory?" (did I get that right?). I''m going to need to be able to do this with several DLLs... my current structure is:

CoreEngine.dll -- OpenGL.dll
|
DirectX.dll

etc, etc.

I''ll have about 5 DLLs in total probably.

bkt

Mar 11, 2004 at 5:39 AM

*bumpppy*

pegasus123

Mar 11, 2004 at 5:43 AM

Not sure if the ffg is what u want ...

To get a class from a DLL.
..................................................
// - THEDLL.dll

// - Global class ptr within the dll
CMyClass* g_pClass = NULL;

__declspec(dllexport) HRESULT DllGetClass(CMyClass** ppObj)
{
if (!ppObj)
{
// - Pointer to nothing. SCREAM AND SHOUT !!
assert(0);
return E_FAIL;
}

// - Do we have an instance of our class yet ??
if (!g_pClass)
{
g_pClass = new CMyClass;
}
*ppObj = g_pClass;
return S_OK;
}

McZ

Mar 11, 2004 at 6:51 AM

I have a plugin RenderCore for my rendersystem that is either OpenGL or Direct3D.. I have created an abstract class that the two API''s is derived from

e.g.
Abstract base class


class cRenderCore {

 // some internal member stuff


protected:

 // some shared internal stuff


public:

 cRenderCore() {};
 virtual ~cRenderCore() {};

 /**
  Create(HWND)
  this will create the rendering context in the passed in window
 */
 virtual void Create(HWND hWnd) = 0;

 /**
  BeginFrame()
  Clears the screen, reset the world matrix etc.
 */
 virtual void BeginFrame() = 0;

 /**
  EndFrame()
  Flips the backbuffer
 */
 virtual void EndFrame() = 0;

 /**
  RenderBuffer(cVertexBuffer *vb)
  Renders my unified vertexbuffer
 */
 virtual void RenderBuffer( cVertexBuffer *vb ) = 0;

 // more virtual functions goes here

 // like set material, light etc.

 ...
 ...
};

so then in my app where I want to use my rendersystem I do like this


HWND hwnd; // the window handle

cRenderCore *RenderCore = NULL;

void InitRenderer()
{
 RenderCore = LoadRenderCore( "RenderCoreGL.dll" );

 RenderCore->Create( hwnd );
}

// render loop

do{
 ...

 // render a vertex buffer

 RenderCore->BeginFrame();
 RenderCore->RenderBuffer( vb );
 RenderCore->EndFrame();
 
}while(1);

the ''LoadRenderCore( char *FileName );'' function loads a .Dll file and achives an function using ''GetProcAddress'' then it will call that function wich will return the API implementation of the abstract RenderCore class

bkt

Mar 11, 2004 at 1:27 PM

That's exactly what I want to do.

Do you return the "RenderCore" object with that Load Function? (or return a function that creates the object?)

[edited by - bkt on March 11, 2004 3:14:20 PM]

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