Jan Engelhardt <jengelh@xxxxxxx> wrote: > """it [the array size expression] shall be a converted constant expression of > type std::size_t and its value shall be greater than zero.""" > —http://eel.is/c++draft/dcl.array Interesting. You're not actually quoting the full sentence: If the constant-expression is present, it shall be a converted constant expression of type std::size_t and its value shall be greater than zero. This suggests that: __u64 ptr[] is actually valid since: D1 [ constant-expressionopt ] attribute-specifier-seqopt suggests that the part between the brackets is optional. David