Re: What does zero-length array mean at file scope?

[Andrew Haley <aph at redhat dot com>]

Dave Korn wrote:
> Dave Korn wrote:
>> Dave Korn wrote:
>>> I've read http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html about six
>>> times and can't see anywhere it even hints that you can use this syntax
>>> anywhere except as the trailing member of a struct.
>> Andrew Haley wrote:
>>> But zero-length arrays are a gcc extension.  There's nothing that limits
>>> them to the last member of a struct.  zero-length arrays must be rejected
>>> with -pedantic, but not otherwise.
>>> Because it's a documented gcc extension.
>>   Obviously I can't see for looking; can you please point me to the precise
>> chapter/page/paragraph/line that I should have found earlier?

"Zero-length arrays are allowed in GNU C.  They are very useful as the
last element of a structure ..."

That doesn't in any way imply that the last element of a struct is the only
circumstance in which you may use a zero-length array.

>   (I honestly mean that, no sarcasm intended; it was late at night and I was
> tired, I could easily have misread or overlooked something.)  I did find this
> comment in varasm.c:assemble_noswitch_variable() that says we need to handle
> this case:
> 
>   /* Don't allocate zero bytes of common,
>      since that means "undefined external" in the linker.  */
>   if (size == 0)
>     rounded = 1;
> 
> ... so I guess it counts as a backend bug if the backend still emits a zero in
> the .comm directive, and that the documentation of ASM_OUTPUT.*COMMON should
> probably be improved to warn of the danger that size may be zero.

Yes.  That's what is usually done: all you have to do is fix the back end.

Andrew.