Copying the Owner vs Copying the Viewer

1#include <iostream>
2using namespace std;
3 
4class Engine {
5public:
6    int hp;
7    Engine(int h) : hp(h) {}
8};
9 
10class Owner {
11    Engine* m_engine;
12public:
13    Owner(int hp) { m_engine = new Engine(hp); }
14    Owner(const Owner& other) { m_engine = new Engine(*other.m_engine); }
15    ~Owner() { delete m_engine; }
16    void tune(int extra) { m_engine->hp += extra; }
17    int hp() const { return m_engine->hp; }
18};
19 
20class Viewer {
21    Engine* m_engine;
22public:
23    Viewer(Engine* e) { m_engine = e; }
24    void tune(int extra) { m_engine->hp += extra; }
25    int hp() const { return m_engine->hp; }
26};
27 
28int main() {
29    Owner o1(100);
30    Owner o2 = o1;
31    o2.tune(50);
32    cout << o1.hp() << " " << o2.hp() << endl;
33 
34    Engine shared(100);
35    Viewer v1(&shared);
36    Viewer v2 = v1;
37    v2.tune(50);
38    cout << v1.hp() << " " << v2.hp() << " " << shared.hp << endl;
39    return 0;
40}