Why class { int i; }; is not fully standard-conformant?

Question

This is a follow-up question.

In the previous question, @JohannesSchaub-litb said that the following code is not fully standard-conformant:

Answer 1

The error message from GCC explains it quite succinctly:

$ cat > a.cc
class { int i; };
$ g++ -Wall -std=c++98 a.cc
a.cc:1: error: abstract declarator ‘’ used as declaration

class { int i; } is an abstract-declarator (Standard, §8) but not a valid declaration (§7). That's the rule that @JohannesSchaub-litb referenced: for a valid declaration, you need something to be declared, e.g. a class name or variable name.