

“ANSI C” by Kernighan and Ritchie disagrees , including that syntax (note : retranslation from Polish as that’s the language my copy is in) :
A8.3
[…]
struct-union-specifier:
, union-struct identifier ₒₚₜ{compound-declaration-list}
, union-struct identifier[…]
Specifiers of structures or unions with [a compound declaration] list, but with no label [identifier], creates a unique type; it may only be referred to in the declaration in which it is part.









I would recommend codeabbey.com
potential bias disclaimer : I have written a CLI to interface with codeabbey