Annex F (informative) Core undefined behavior [ub]

F.6 [class]: Classes [ub.class]

F.6.7[ub:class.cdtor.form.pointer]
Specified in: [class.cdtor]

When forming a pointer to a direct non-static member of a class, construction must have started and destruction must not have finished otherwise the behavior is undefined.
[Example 1: struct A { int i = 0; }; struct B { int *p; A a; B() : p(&a.i) {} // undefined behavior }; — end example]