What does define COMMENT_ONLY mean?

[Vladimir Budnev]

On 07/23/11 04:21, Bruce Evans wrote:
>
> C didn't support support variable-sized structs before C99, and
> doesn't really support them now.  Various hacks are used to make
> pseudo-structs larger or smaller than ones that can actually be
> declared work.  The above is one.  The pseudo-struct is malloc()ed
> and has size larger than the declared one.  The above says what
> would be in it if it could be declared.
>
> If this were written in C99, it might declare u_char ar_foo[] in the
> the code instead of in a comment.  But C can't really support variable-
> sized structs.  It only allows one ar_foo[], which must be at the end
> of the struct.  ar_foo then has a known offset but an unknown size.
> The other ar_bar[]'s still can't be declared, since they want to be
> further beyond the end of the struct, which places them at an unknown
> offset.
>
> A probably-less-unportable way was to declare everything in the struct
> but malloc() less.  This only works if all the magic fields are at
> known offsets.  This doesn't work in the above, since the fields want
> to have variable lengths each and thus end up at variable offsets.
> Such fields can be allocated from a single larger field (usually an
> an array), but you lose the possibility of declaring them all.
>
> Bruce

I got the idea with "dynamic size", tnx:) But comment_only ...ah 
nevermined. Tnx for explanation, Bruce.