Call this function within your control's DoPropExchange member function to serialize or initialize a property represented by an object having an IUnknown-derived interface.
BOOL PX_IUnknown( CPropExchange* pPX, LPCTSTR pszPropName, LPUNKNOWN& pUnk, REFIID iid, LPUNKNOWN pUnkDefault = NULL );
Pointer to the CPropExchange object (typically passed as a parameter to DoPropExchange).
The name of the property being exchanged.
Reference to a variable containing the interface of the object that represents the value of the property.
An interface ID indicating which interface of the property object is used by the control.
Default value for the property.
Nonzero if the exchange was successful; 0 if unsuccessful.
The property's value is read from or written to the variable referenced by pUnk, as appropriate. If pUnkDefault is specified, it will be used as the property's default value. This value is used if, for any reason, the control's serialization process fails.