Re: Struct Error

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.