What can i return if i'm working with a pointer on a const function?

Question

class class_B
{
    class_A* A;

.
.
.

    class_A& func() { return *A; }
    class_A func() const { return *A; }

ostream& operator <<(ostream& os, const class_B& obj)
{
    os << obj.func();
    return os;
}

this give me an error but i don't understand why.

Do I have to implement class_A's copy/move constructor/operator?

Answer 1

Return a const reference:

const class_A& func() const { return *A; }