IIDNULL

IIDNULL is a sentinel value used in some programming environments to denote a null or unspecified interface identifier (IID). It corresponds to a GUID (globally unique identifier) with all zero bits, typically written in its canonical form as 00000000-0000-0000-0000-000000000000. In Windows COM and related systems, interface identifiers are GUIDs that uniquely identify interfaces.

The primary role of IIDNULL is to signal that no particular interface is being requested or that an interface ID has not been initialized. It is distinct from any valid interface identifier, such as IID_IUnknown or other IIDs defined for specific interfaces. While many platforms use the name IID_NULL or GUID_NULL, some codebases may refer to the value as IIDNULL depending on language, headers, or documentation.

Usage and semantics can vary by framework. In practice, developers may compare an IID against IIDNULL to detect an uninitialized or unavailable interface ID, using appropriate GUID comparison routines (for example, a function like IsEqualIID or a direct bytewise comparison). It is important to consult the specific API or header documentation to understand acceptable inputs, as some APIs may reject IIDNULL and require a concrete interface ID.

See also: GUID, GUID_NULL, IID, IID_IUnknown, QueryInterface.