Re: std::vector and a bit-wise copy

I have a question that I having trouble finding a straight answer to,
but thought it may be obvious to someone here.

If I have a struct with a vector as a member:

struct A
{
    std::vector<int> theVec;

};

And I make two instances of that vector x and y and populate the
vector in x. Is it undefined behavior to then set y= x ? Such as

int main()
{
    A x;
    A y;

    fill(x); // allocates the vector and populates it

    y = x;

}

Seeing A has no copy-constructor declared, we should do a bit-wise
copy from x to y. Since the vector in y has no memory allocated to it,
I'm assuming this should be just a case of memory trampling and
exhibit UB.

Is that wrong or am I missing something w.r.t. the bit-wise copy?