Re: [PATCH v8 1/5] Provide counted_by attribute to flexible array member field (PR108896)

[Joseph Myers <josmyers@redhat.com>]

On Fri, 29 Mar 2024, Qing Zhao wrote:

> +  /* Issue error when there is a counted_by attribute with a different
> +     field as the argument for the same flexible array member field.  */

There's another case of this to consider, though I'm not sure where best 
to check for it (Martin might have suggestions) - of course this case will 
need testcases as well.

Suppose, as allowed in C23, a structure is defined twice in the same 
scope, but the two definitions of the structure use inconsistent 
counted_by attributes.  I'd say that, when the declarations are in the 
same scope (thus required to be consistent), it should be an error for the 
two definitions of what is meant to be the same structure to use 
incompatible counted_by attributes (even though the member declarations 
are otherwise the same).

In C23 structures defined with the same tag in different scopes are 
compatible given requirements including compatible types for corresponding 
elements.  It would seem most appropriate to me for such structures with 
incompatible counted_by attributes to be considered *not* compatible types 
(but it would be valid to define structures with the same tag, different 
scopes, and elements the same except for counted_by - just not to use them 
in any way requiring them to be compatible).

> +The @code{counted_by} attribute may be attached to the C99 flexible array
> +member of a structure.  It indicates that the number of the elements of the
> +array is given by the field "@var{count}" in the same structure as the

As noted previously, the "" quotes should be removed there (or replaced by 
``'' quotes).

-- 
Joseph S. Myers
josmyers@redhat.com