Category 

Modifiers, Keyword extensions, Storage class specifiers 

Syntax  

__declspec( uuid(“ComObjectGUID”) ) declarator

The compiler attaches a GUID to a class or structure declared or defined (full COM object definitions only) with the uuid attribute. The uuid attribute takes a string as its argument. This string names a GUID in normal registry format with or without the { } delimiters. For example:  

struct __declspec(uuid("00000000-0000-0000-c000-000000000046")) IUnknown; 

struct __declspec(uuid("{00020400-0000-0000-c000-000000000046}")) IDispatch; 

This attribute can be applied in a redeclaration. This allows the system headers to supply the definitions of interfaces such as IUnknown, and the redeclaration in some other header (such as COMDEF.H) to supply the GUID. 

The keyword __uuidof can be applied to retrieve the constant GUID attached to a user-defined type.