> On Apr 10, 2024, at 15:05, Martin Uecker <uec...@tugraz.at> wrote: > > Am Mittwoch, dem 10.04.2024 um 20:25 +0200 schrieb Martin Uecker: >> Am Mittwoch, dem 10.04.2024 um 17:35 +0000 schrieb Joseph Myers: >>> 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). >> >> I think the right place could be comp_types_attributes in >> attributes.cc. It may be sufficient to set the >> affects_type_identify flag. >> >> This should then give a redefinition error as it should do for >> "packed". > > Thinking about this a bit more, this will not work here, because > the counted_by attribute is not applied to the struct type but > one of the members. > > So probably there should be a check added directly > to tagged_types_tu_compatible_p
There are two cases we will check: A. Both definitions are in the same scope; Then if the 2nd definition has a counted-by attribute different from the 1st definition, the 2nd definition will be given a redefinition error; B. These two definitions are in different scope; When these two definitions are used in a way need to be compatible, an incompatible error need to be issued at that Point; My question is, Will the routine “tagged_types_tu_compatible_p” can handle both A and B? Thanks. Qing > > Martin > >> >>> >>> 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). >> >> Another option might be to warn about the case when those types >> are then used together in a way where they are required to >> be compatible. Then comp_types_attributes would have to return 2. >> >> >> Martin >> >>> >>>> +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). >>> >> >