westonpace commented on issue #35226:
URL: https://github.com/apache/arrow/issues/35226#issuecomment-1516558160
Null values are not guaranteed to be 0. We use a separate bitmask validity
vector to determine if an element is null or not. If an element is null then
it's value is undefined and could be anything.
However, creating spans from buffers is fine.
Those spans will not keep the buffer alive though. So you need to avoid
something like this:
```
std::span GetMyData() {
std::shared_ptr<Array> m_array = GetSomeArray();
auto ptr = reinterpret_cast<const
double*>(m_array->data()->buffers[1]->data()) + m_array->offset();
std::span view(ptr, m_array->length);
return view;
}
```
Also, that reinterpret cast is only valid if
`m_array->data()->buffers[1]->data()` is 8-byte aligned. This is true for any
buffer allocated by Arrow-C++ and is supposed to be true for any buffer sent
over IPC but it is not currently guaranteed for buffers received over Flight
due to https://github.com/apache/arrow/issues/32276.
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