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From: Michael S <already5chosen@yahoo.com>
Newsgroups: comp.lang.c
Subject: Re: Struct Error
Date: Fri, 24 Jan 2025 16:37:40 +0200
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On Thu, 23 Jan 2025 10:54:10 +0000
bart <bc@freeuk.com> wrote:

> On 23/01/2025 01:05, James Kuyper wrote:
> > On 2025-01-22, bart <bc@freeuk.com> 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)[];
> >>     };  
> > 
> > 6.7.6.2p2: "The element type shall not be an incomplete or function
> > type."
> > 
> > I have many draft versions of the C standard. n2912.pdf, dated
> > 2022-06-08, says in 6.7.2.1.p3 about struct types that "... the
> > type is incomplete144) until immediately after the closing brace of
> > the list defining the content, and complete thereafter."
> > 
> > Therefore, struct scenet is not a complete type until the closing
> > brace of it's declaration.  
> 
> Wouldn't this also be the case here:
> 
>     struct scenet *child;
>    };
> 

Just to point out if it was not said already: the problem is not related
specifically to recursive structures. It applies to arrays of
incomplete types in all circumstances.

struct bar;
struct bar (*bag)[]; // error
typedef struct bar (*bat)[]; // error

The case of the recursive structure is special only in a sense that it's
o.k. in C++, because [unlike C] in C++ struct considered complete within
its own body.