> On Nov 20, 2025, at 12:40, Joseph Myers <[email protected]> wrote:
>
> On Wed, 19 Nov 2025, Qing Zhao wrote:
>
>> Hi,
>>
>> For the following two cases:
>>
>> A. Anonymous structure type is a top-level type:
>>
>> struct {
>> int a;
>> char c[] __attribute__ ((counted_by (a)));
>> };
>>
>> B. Anonymous structure type is the type for an unnamed field of another
>> structure:
>>
>> struct s {
>> int a;
>> struct {
>> int b;
>> char c[] __attribute__ ((counted_by (a)));
>> };
>> };
>>
>>
>> My question:
>>
>> When C FE sees the above two anonymous structure type in A and B, how to
>> distinguish them?
>
> That's not the right distinction to make, since you can modify B
>
> struct s {
> int a;
> struct {
> int b;
> char c[] __attribute__ ((counted_by (a)));
> } x;
> };
>
> and adding the name to the field means it no longer has any of the special
> effects on name lookup.
As Martin mentioned before, can the following
c_type_tag (type) == NULL_TREE && DECL_NAME (field) == NULL_TREE
Be the condition?
> The logic that determines whether a particular unnamed field declaration
> is valid as an anonymous struct / union (with the associated special
> properties) is in grokfield.
Thanks for the info, will take a look at the logical there.
> This is not a property of the anonymous
> struct / union itself, but of how it is used when declaring a field of an
> outer struct / union.
Okay, thanks.
Qing
>
> --
> Joseph S. Myers
> [email protected]
>
