C++ overwriting data from parent structure is not working - c++

Question

Normally it has no sense and is very unsafe, but only theoretically if there is a way,
Here is example:
#include<iostream>
struct A {
uint32_t &get() {
return *reinterpret_cast<uint32_t *>(this);
}
void set(const uint32_t val) {
*this = *reinterpret_cast<const A *>(&val);
}
};
struct B : A {
uint16_t a;
uint16_t b;
void set_b(const uint32_t val) {
*this = *reinterpret_cast<const B *>(&val);
}
};
main() {
B k;
k.a = 0x1234;
k.b = 0x5678;
std::cout << std::hex << k.get() << " : " << k.a << " " << k.b << std::endl;
k.set_b(0x87654321);
std::cout << std::hex << k.get() << " : " << k.a << " " << k.b << std::endl;
k.set(0xaabbccdd);
std::cout << std::hex << k.get() << " : " << k.a << " " << k.b << std::endl;
}
I get this result:
56781234 : 1234 5678
87654321 : 4321 8765
87654321 : 4321 8765
But I except that last should be:
aabbccdd : ccdd aabb
So, why overwriting data in structure from parent not working?
Experiment:
I make one experiment, that I add one variable into struct A, then set function was working as expected (but final structure was bigger)
Of course there exists different ways how to deal with this (for example with unions) but I only playing with this and I interested why this is not working.

Answer 1

In the class A the set function is really
void set(const uint32_t val) {
(*this).operator=(*reinterpret_cast<const A *>(&val));
}
That will invoke the automatically generated A::operator= function. But since A doesn't have any member variables to be copied, it does nothing.
And now that you've done your experiment, please don't do anything like that ever again.