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On Sun, Nov 10, 2024 at 8:57 PM Jens Maurer <jens.maurer_at_[hidden]> wrote:

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> On 10/11/2024 21.45, Mykola Garkusha via Std-Discussion wrote:
> > Hi all,
> >
> > Currently(unlike C), the standard does not guarantee that padding bits
> may retain specific values even between sequential reads. Let's exclude
> tail padding re-use for potentially-overlapping sub-objects. as it is a
> slightly different matter related to OOP in C++ .
> >
> > In C, padding bits are guaranteed to say the same unless you modify the
> value!
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> Yes.
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> > Also looks like Clang and GCC also follow it, particularly to
> facilitate atomic operations on objects with padding bits.
> > Clang and GCC even go further by providing intrinsics to clear padding
> bits (for example *__builtin_clear_padding* in GCC).
> >
> > Is there any chance C++ standard would allow this officially to come
> closer to the behaviour in C?
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> How would you want to inspect those padding bits portably? And why?
> What's the use-case?
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     I don't see anything radically different compared to C, hence I hope
portability would not be an issue. The main benefit of this change would be
the ability to compare objects using object representation which is much
faster. Say one could ensure padding bits set to 0 on creation or during
the lifetime of an object and later compare the object with *memcmp *knowing
ahead that the object value does not change and even it does one could
again reset padding bits to 0 to use *memcmp*

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> Jens
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