Is segmentation fault actual undefined behavior when we refer to a non-static data-member

Question

I had read the following rule and I\'ve been trying to write an example, which reflects one. The rule is from 3.8/5 N3797:

Before the lifetime of an o

Answer 1

You asked:

Is it true that in the case //1 is well-formed and doesn't cause any UB?

The parts of the standard you quoted does not mention anything about it.

You also asked:

but //2 produced segmentation fault, which is UB?

The parts of the standard you quoted does not correspond to this particular behavior. You are seeing UB because of where p points. It points to memory that does not hold a valid object.