How to return new object in COM?

[ryu]

Hi GURUs,

I have created a new COM DLL and just wondering how to return a new COM object.

Here is my code to return a new object.

HRESULT __stdcall CMainTestClass::GetSamTest(IAdd **ppRetVal)
{
    CAddClass *pAddClass = new CAddClass();
    *ppRetVal = pAddClass;
    return S_OK;
}

When I call this function in C#, it gave me this error:

The runtime has encountered a fatal error. The address of the error was at 0x7f628678, on thread 0x105c. The error code is 0xc0000005. This error may be a bug in the CLR or in the unsafe or non-verifiable portions of user code. Common sources of this bug include user marshaling errors for COM-interop or PInvoke, which may corrupt the stack.

My C# code:

    MyTestLib.MainTestClass oMainObject = new MyTestLib.MainTestClass();
    MyTestLib.AddClass addObject = (oMainObject .GetSamTest() as MyTestLib.AddClass );
    MessageBox.Show(addObject.DoTheAddition().ToString());    //it fails here

Thanks for any help

[cilu]

Here are some tutorials on COMs
http://www.codeproject.com/KB/COM/comintro.aspx
http://www.codeproject.com/KB/COM/comintro2.aspx
http://www.codeguru.com/cpp/com-tech...icle.php/c5529
http://www.codeguru.com/cpp/com-tech...cle.php/c5533/

[PadexArt]

If you use ATL you can do this through CComObject's CreateInstance :

STDMETHODIMP CMainTestClass::GetSamTest(IAdd **ppRetVal)
{
	CComObject<CAddClass>* addObj = NULL;
	HRESULT hRes = CComObject<CAddClass>::CreateInstance(&addObj);
	_ASSERTE(SUCCEEDED(hRes));

	// Increment reference count immediately
	addObj ->AddRef();

	addObj ->QueryInterface( IID_IAdd, (void**) ppRetVal);

	return S_OK;
}

[ryu]

Hi PadexArt & Cilu,

Thanks for your help. You guys have been really helpful

Cheers