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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Struct Error
Date: Wed, 22 Jan 2025 23:11:54 -0800
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Xref: csiph.com comp.lang.c:390104

bart <bc@freeuk.com> writes:

> 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?
>
> (This comes from generated code.  Idiomatic C would use a T* here
> rather than T(*)[], but that is not an option.  Other compilers like
> tcc, DMC and mine have no problem with it.)

The code shown violates a constraint in the C standard, because
the element type of the array declarator is an incomplete type
at the point the 'child' member is declared, so a diagnostic
is required.