HRESULT CoCreateInstance(
  REFCLSID rclsid,     // Class identifier (CLSID) of the object to be created
  LPUNKNOWN pUnkOuter, // Pointer to controlling IUnknown (for aggregation)
  DWORD dwClsContext,  // Context in which the code that manages the newly created object will run
  REFIID riid,         // Interface identifier (IID) of the interface to be used to communicate with the object
  LPVOID *ppv          // Address of pointer variable that receives the interface pointer requested in riid
);

IMMDeviceEnumerator* deviceEnumerator = NULL;
HRESULT hr = CoCreateInstance(
    __uuidof(MMDeviceEnumerator),  // CLSID
    NULL,                          // pUnkOuter (no aggregation)
    CLSCTX_ALL,                    // Context
    __uuidof(IMMDeviceEnumerator), // IID
    (void**)&deviceEnumerator      // Interface pointer
);

class COuter : public IUnknown {
public:
    // Implement IUnknown methods
    HRESULT QueryInterface(REFIID riid, void** ppv) {
        if (riid == IID_IUnknown) {
            *ppv = static_cast<IUnknown*>(this);
            AddRef();
            return S_OK;
        }
        // Handle other interfaces
        return E_NOINTERFACE;
    }

    ULONG AddRef() {
        return InterlockedIncrement(&m_refCount);
    }

    ULONG Release() {
        ULONG count = InterlockedDecrement(&m_refCount);
        if (count == 0) {
            delete this;
        }
        return count;
    }

private:
    ULONG m_refCount;
};

// Create an instance of COuter and aggregate CInner
COuter* pOuter = new COuter();
IUnknown* pUnkOuter = static_cast<IUnknown*>(pOuter);
CInner* pInner = NULL;

HRESULT hr = CoCreateInstance(
    CLSID_CInner,         // CLSID of the inner object
    pUnkOuter,            // pUnkOuter (aggregation)
    CLSCTX_INPROC_SERVER, // Context
    IID_IUnknown,         // IID of the interface
    (void**)&pInner       // Interface pointer
);

if (SUCCEEDED(hr)) {
    // Use pInner
}