Re: [hub] Andrzej's review

Peter Dimov via Boost <[email protected]>
Newsgroups gmane.comp.lib.boost.devel
Message-ID <[email protected]>
Andrzej Krzemienski wrote:
> 5. Compiling with -Wall gives me a warning in GCC when sorting an empty
> hub: a zero-sized heap array is allocated:
> https://godbolt.org/z/dWvxv9n8s
> This is technically fine to allocate such arrays, but maybe it is worth to
> make -Wall clean.

The warning isn't caused by the zero sized allocation (which is legal.)

It's because the compiler can see that the array has zero elements, but
can't see that the loop inside this call to visit

https://github.com/joaquintides/hub/blob/063cf1d3589d4893b53964084ee56f4476eed471/include/boost/container/hub.hpp#L1628

is never executed. So it says "if this loop is executed, it would be UB
because there aren't any elements there" but this is a false positive
because the loop isn't executed.

(The subsequent loops suffer from the same issue and also cause
warnings for the same reason.)

A common problem with GCC, and unfortunately nothing can be
done about it short of disabling the warning.


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