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NNTP-Posting-Date: Mon, 22 Oct 2012 10:13:05 -0500
From: Steve Thompson <stevet810@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Compatibility question
Date: Mon, 22 Oct 2012 02:28:43 +0000
Organization: Friends of the Galactic Collective
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On Mon, Oct 22, 2012 at 02:27:01AM +0100, Ben Bacarisse wrote:
> Steve Thompson <stevet810@gmail.com> writes:
> 
> > On Mon, Oct 22, 2012 at 12:29:08PM +1300, Ian Collins wrote:
> >> On 10/22/12 11:54, Steve Thompson wrote:
> <snip>
> >> >Now that I've noticed that the GCC documentation has been updated (I
> >> >may not have read that section for ten years, now that I think of it),
> >> >it does indeed say that the C99 standard includes support for flexible
> >> >arrays, with similar semantics to the old gcc zero subscript hack, so
> >> >I will use that.
> >> 
> >> You can't use a VLA as a structure member (how would you declare it?).
> >
> >>From the GCC info pages:
> >
> >   In ISO C99, you would use a "flexible array member", which is slightly
> > different in syntax and semantics:
> >
> >    * Flexible array members are written as `contents[]' without the `0'.
> >
> >    * Flexible array members have incomplete type, and so the `sizeof'
> >      operator may not be applied.  As a quirk of the original
> >      implementation of zero-length arrays, `sizeof' evaluates to zero.
> >
> >    * Flexible array members may only appear as the last member of a
> >      `struct' that is otherwise non-empty.
> >
> >    * A structure containing a flexible array member, or a union
> >      containing such a structure (possibly recursively), may not be a
> >      member of a structure or an element of an array.  (However, these
> >      uses are permitted by GCC as extensions.)
> >
> > So I'm free and clear.  My VLAs will be in structures which are not
> > encapsulated in other structures.
> 
> There's a terminology confusion here.  Your flexible array member is
> just that, it's not a VLA.  Variable length arrays are not permitted in
> structs and flexible array members can only appear, unsurprisingly, in a
> struct.

I suppose so.  Simply stated, anytime I use "something foo[]", it will
usually be at the end of a struct.  Good enough?

Really, you ought to have read what I meant, rather than reading what I
wrote.



Regards,

Steve Thompson

-- 
GOTO's are like guns.  Safety is entirely contingent on the user.