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From: Andrey Tarasevich <noone@noone.net>
Newsgroups: comp.lang.c
Subject: Re: Struct Error
Date: Sun, 2 Feb 2025 20:35:59 -0800
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On Wed 1/22/2025 8:14 AM, bart wrote:
> Gcc 14.1 gives me an error compiling this code:
> 
>    struct vector;
>    struct scenet;
> 
>    struct vector {
>        double x;
>        double y;
>        double z;
>    };
> 
>    struct scenet {
>        struct vector center;
>        double radius;
>        struct scenet (*child)[];
>    };
> 
> The error is:
> 
>    error: array type has incomplete element type 'struct scenet'
>     struct scenet (*child)[];
>                    ^~~~~
> 
> Is there any way to fix this, or is it not possible?

C has always been very strict about completeness of the element type in 
array declarations. The element type has to be complete, period.

Another manifestation of the same issue is demonstrated by the following 
example

   struct S;
   void foo(struct S a[]) {}

The function parameter declaration is invalid in C sue to incompleteness 
of `struct S`. Even though the declaration will be implicitly adjusted 
anyway to

   void foo(struct S *a) {}

and this adjusted version is perfectly valid the in C (despite 
incompleteness of `struct S`), the language still rejects the original 
variant.

C++ is more lenient in such contexts.

-- 
Best regards,
Andrey