On 2/18/25 00:16, Andrey Semashev wrote:
> On 2/17/25 23:09, Vladimir Grigoriev via Std-Discussion wrote:
>> In p. 5 of the section 6.2 Declarations and definitions of the C++23
>> Standard there is written
>>
>> 5 In the definition of an object, the type of that object shall not be
>> an incomplete type (6.8), an abstract class type (11.7.4), or a
>> (possibly multi-dimensional) array thereof
>>
>> Also in p.5 of the sub-section 6.8.1 General of the section 6.8 Types
>> there is written
>>
>> ...The type of a pointer to array of unknown bound, or of a type defined
>> by a typedef declaration to be an array of unknown bound, cannot be
>> completed.
>>
>> And further there is followed an example (Example 3)
>>
>> class X; // X is an incomplete type
>> extern X* xp; // xp is a pointer to an incomplete type
>> extern int arr[]; // the type of arr is incomplete
>> typedef int UNKA[]; // UNKA is an incomplete type
>> UNKA* arrp; // arrp is a pointer to an incomplete type
>> UNKA** arrpp;
>>
>> But according to the first provided quote this object definition
>>
>> UNKA* arrp; // arrp is a pointer to an incomplete type
>>
>> is invalid because such a pointer has an incomplete type.
>>
>> So it looks like the example does not make sense or do I have missed
>> something?
>
> I'm not sure which version of the standard you're reading, but the
> current wording is different. I'm guessing you're referring to Note 2 in
> paragraph 6:

I meant Note 3, sorry for the typo.

> http://eel.is/c++draft/basic.types.general#6
>
> <quote>
> The type of a pointer or reference to array of unknown bound permanently
> points to or refers to an incomplete type.
> An array of unknown bound named by a typedef declaration permanently
> refers to an incomplete type.
> In either case, the array type cannot be completed.
> </quote>
>
> Note the text refers to the *array* type, not the *pointer* type. The
> pointer type itself is always complete, even if the pointee type is
> incomplete.
>