class-key attribute-specifier-seq identifier ;the identifier is looked up according to [basic.lookup.unqual] but ignoring any non-type names that have been declared.
class-key attribute-specifier-seq identifier ;the elaborated-type-specifier is a declaration that introduces the class-name as described in [basic.scope.pdecl].
struct Node {
struct Node* Next; // OK: Refers to Node at global scope
struct Data* Data; // OK: Declares type Data at global scope and member Data
};
struct Data {
struct Node* Node; // OK: Refers to Node at global scope
friend struct ::Glob; // error: Glob is not declared, cannot introduce a qualified type ([dcl.type.elab])
friend struct Glob; // OK: Refers to (as yet) undeclared Glob at global scope.
/* ... */
};
struct Base {
struct Data; // OK: Declares nested Data
struct ::Data* thatData; // OK: Refers to ::Data
struct Base::Data* thisData; // OK: Refers to nested Data
friend class ::Data; // OK: global Data is a friend
friend class Data; // OK: nested Data is a friend
struct Data { /* ... */ }; // Defines nested Data
};
struct Data; // OK: Redeclares Data at global scope
struct ::Data; // error: cannot introduce a qualified type ([dcl.type.elab])
struct Base::Data; // error: cannot introduce a qualified type ([dcl.type.elab])
struct Base::Datum; // error: Datum undefined
struct Base::Data* pBase; // OK: refers to nested Data
— end example