Three Files: Composition Across Headers

1// ===== Car.h =====
2#ifndef CAR_H
3#define CAR_H
4#include <iostream>
5#include <string>
6 
7class Engine {
8    int m_hp;
9public:
10    Engine(int hp) : m_hp(hp) { std::cout << "Engine " << m_hp << std::endl; }
11    ~Engine() { std::cout << "~Engine " << m_hp << std::endl; }
12    int hp() const { return m_hp; }
13};
14 
15class Car {
16    std::string m_model;
17    Engine m_engine;
18public:
19    Car(const std::string& model, int hp);
20    ~Car();
21    void show() const;
22};
23 
24#endif
25 
26// ===== Car.cpp =====
27#include <iostream>
28#include "Car.h"
29using namespace std;
30 
31Car::Car(const string& model, int hp) : m_model(model), m_engine(hp) {
32    cout << "Car " << m_model << endl;
33}
34 
35Car::~Car() {
36    cout << "~Car " << m_model << endl;
37}
38 
39void Car::show() const {
40    cout << m_model << " has " << m_engine.hp() << " hp" << endl;
41}
42 
43// ===== main.cpp =====
44#include <iostream>
45#include "Car.h"
46using namespace std;
47 
48int main() {
49    Car a("Civic", 158);
50    {
51        Car b("Golf", 147);
52        b.show();
53    }
54    a.show();
55    return 0;
56}