Will an 'empty' constructor or destructor do the same thing as the generated one?

Question

Suppose we have a (toy) C++ class such as the following:

class Foo {
    public:
        Foo();
    private:
        int t;
};

Since no des

Answer 1

An empty definition is fine since the definition can be referenced

virtual ~GameManager() { };

The empty declaration is deceptively similar in appearance

virtual ~GameManager();

yet invites the dreaded no definition for virtual destructor error

Undefined symbols:
  "vtable for GameManager", referenced from:
      __ZTV11GameManager$non_lazy_ptr in GameManager.o
      __ZTV11GameManager$non_lazy_ptr in Main.o
ld: symbol(s) not found