Members are built first – OOP in C++ Practice Problem

An object that contains other objects is built from the inside out, and taken apart from the outside in.

What to build

A Room class with two Part members, whose constructors and destructors report when they run.

Requirements

Part prints part NAME made when built and part NAME removed when destroyed.
Room holds two Part members, declared first and second, and prints room NAME made and room NAME closed.
Build the parts in Room's member initializer list.
Keep main as it is.

Input

One line with three words: the room's name, the first part's name and the second part's name.

Output

Seven lines, in the order the constructors, main and the destructors print them.

Constraints

Each name is one word.

Example

Input:

Kitchen sink oven

Output:

part sink made
part oven made
room Kitchen made
in use
room Kitchen closed
part oven removed
part sink removed

Why it works

C++ builds members before the constructor body so that the body can use them, in their declared order. Destruction mirrors construction exactly, so the members outlive the destructor body that might still need them.

Examples

Example 1 · Input

Kitchen sink oven

Expected output

part sink made
part oven made
room Kitchen made
in use
room Kitchen closed
part oven removed
part sink removed

Example 2 · Input

Lab desk lamp

Expected output

part desk made
part lamp made
room Lab made
in use
room Lab closed
part lamp removed
part desk removed

Hints

Hint 1

Member objects are built before the body of the class's own constructor runs, in the order they are declared in the class.

Hint 2

They are destroyed after the body of the class's own destructor, in reverse order.

Hint 3

Pass the part names to the members in the member initializer list.

Solution

Show one correct solution (try it yourself first)

#include <iostream>
#include <string>
using namespace std;

class Part {
    string name;
public:
    Part(string n) : name(n) {
        cout << "part " << name << " made" << endl;
    }
    ~Part() {
        cout << "part " << name << " removed" << endl;
    }
};

class Room {
    string name;
    Part first;
    Part second;
public:
    Room(string r, string a, string b) : name(r), first(a), second(b) {
        cout << "room " << name << " made" << endl;
    }
    ~Room() {
        cout << "room " << name << " closed" << endl;
    }
};

int main() {
    string r, a, b;
    cin >> r >> a >> b;
    Room room(r, a, b);
    cout << "in use" << endl;
    return 0;
}

Lesson: Constructors and destructors →