Access sub object in COM interface - c++

Question

I want to get access to a sub object of a COM object. In my example I use the CANoe COM Server.
In my program I create a CAN interface to the CANoe Application. Here is an extract of my code so far and it does exactly what I want:
HRESULT result;
//prepare for COM handling...
result = CoInitialize(NULL);
//get CLSID of CANoe...
result = CLSIDFromProgID(L"CANoe.Application", &clsid);
if(SUCCEEDED(result))
{
//connect to COM interface of CANoe...
result = CoCreateInstance(clsid, NULL, CLSCTX_LOCAL_SERVER | CLSCTX_REMOTE_SERVER, IID_IApplication, (void**) &pIApp);
if(SUCCEEDED(result))
{
qDebug() << "COM connection established";
}
else
{
qDebug() << "COM connection error";
}
}
else
{
qDebug() << "Error: CLSID";
}
Now I want to get access to a sub object of the COM Server. For example the Measurement object. I tried it with the method pIApp->get_UI()
IDispatch* pIDis;
IMeasurement* pIMeasurement;
result = pIApp->get_UI(&pIDis);
pIMeasurement = (IMeasurement*) pIDis;
The pointer to the COM object needs to be a pointer of the type IMeasurement, so I can use all the methods defined in the header file. But the method get_UI only supports pointer of the type IDispatch. I tried to cast the pointer from type IDispatch to IMeasurement. But the program crashs at runtime.
I also tried to create a new interface directly to the sub object:
result = CoCreateInstance(clsid, NULL, CLSCTX_LOCAL_SERVER | CLSCTX_REMOTE_SERVER, IID_IMeasurement, (void**) &pIMeasurement);
But in this try in the variable result there is saved an error and I can't access the methods of the sub object Measurement.
Where is my mistake and how can I get access to the sub object?
Thank you for all answers and hints!

Answer 1

Thanks to #WhozCraig, #Hans Passant and #Eric Brown for the hints in the comments.
I was able to solve my problem with the following code:
IDispatch* pIDispatch;
//get pointer pIDispatch to Measurement object of CANoe...
result = pIApp->get_Measurement(&pIDispatch);
if(SUCCEEDED(result))
{
//pointer pIDispatch to pIMeasurement...
result = pIDispatch->QueryInterface(IID_IMeasurement, (void**) &pIMeasurement);
if(SUCCEEDED(result))
{
pIDispatch->Release();
//work with connection here...
pIMeasurement->Release();
}
}