Cast a _com_ptr_t to void * and then back to _com_ptr_

Question

How do you cast a COM interface pointer to void pointer and then back to the COM pointer? Here is some code to illustrate my problem. It's very similar to this sample code: _com_ptr_t assignment in VC++

CoInitialize(NULL);

COMLib::ICalcPtr pCalc = COMLib::ICalcPtr("MyLibrary.Calculator");

pCalc->doSomething();

CoUninitialize();
return 0;

Now, if I were to cast the pCalc object to void*, how would I cast it back to COMLib::ICalcPtr? For example, the second line in the following code gives me a compile error 'QueryInterface' : is not a member of 'System::Void'. Obviously, it's trying to call IUknown.QueryInterface() on the object. Preferably I would like to do this without creating a new interface (hence, without implicitly calling QueryInterface and AddRef).

void *test = pCalc;
COMLib::ICalcPtr pCalc2 = test;//'QueryInterface' : is not a member of 'System::Void'

FYI, the reason I'm doing this is that the object is going to be passed around from java to jni VC++ code as a void* type. I'm open to any suggestion on what to do or what is going on behind the scene.

Answer 1

Same way you pass any other opaque structure that either doesn't fit in a pointer or doesn't convert easily: by passing its address.

void* test = new COMLib::ICalcPtr(pCalc);

...

COMLib::ICalcPtr pCalc2 = *(COMLib::ICalcPtr*)test;
delete (COMLib::ICalcPtr*)test;

This will result in calls to AddRef and Release, but not QueryInterface.