C++ trick #1

Attenzione a questo tipo di errore a cui sono soggetti gli smart pointer di C++.

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

class Person {
public:
    string name;
    Person(string n)
        : name(n) {}
    ~Person() {
        cout << name << " destroyed" << endl;
    }
};

class Car {
public:
    Car(string d, string p)
        :driver(d)
        ,passenger(p) {}
    string model;
    shared_ptr<Person> drv() { return shared_ptr<Person>(&driver); }
    Person driver;
    Person passenger;
    ~Car() {
        cout << model << " destroyed" << endl;
    }
};

int main()
{
    shared_ptr<Person> drv;
    {
        Car astra("Domenico", "Andrea");
        astra.model = "Astra K";
        drv = astra.drv();
    }
    cout << "Car's scope destroyed" << endl;
    // Do you expect drv in a valid state?
    cout << "Using " << drv->name << endl; // Crash!
    return 0;
}

Compila ed esegui

[ddiiorio@ddiiorio ~]$ g++ main.cpp -o main
[ddiiorio@ddiiorio ~]$ ./main
Astra K destroyed
Andrea destroyed
Domenico destroyed
Car's scope destroyed
Using Domenico10pU����Astra K!�@�f6�QAborted (core dumped)