Undefined behavior on reading object using non-character type when last written using character type

Question

Assuming unsigned int has no trap representations, do either or both of the statements marked (A) and (B) below provoke undefined behavior, why or why not, and

Answer 1

On a superficial examination, I'd agree with your assessment (A is UB, B is fine), and can offer a concrete rationale for why that should be so (prior to the edit to include _Alignas()): Alignment.

The char[] on the stack can start at any address, whether that's a valid alignment for an unsigned int or not. In contrast, malloc() is required to return memory meeting the strictest alignment requirements of any native type on the platform in question.

The standard obviously doesn't want to impose alignment requirements on char[] beyond those of char, so it has to leave type-punned access to it as potentially undefined.