What to do When an Interface You Need is Not Available

This section states some fundamental rules that apply to all OLE programming. OLE programs should use QueryInterface to acquire interface pointers, and must check the return value. OLE applications cannot safely assume that QueryInterface will succeed, this requirement applies to all OLE applications. If the requested interface is not available (i.e., QueryInterface returns E_NOINTERFACE), the control or container must degrade gracefully, even if that means that it cannot perform its designated job function.