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std::enable_shared_from_this

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La gestion dynamique de la mémoire
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Smart pointers
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unique_ptr (C++11)
shared_ptr (C++11)
weak_ptr (C++11)
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enable_shared_from_this (C++11)
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std::enable_shared_from_this
Protégé fonctions membres
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Protected member functions
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enable_shared_from_this::enable_shared_from_this
enable_shared_from_this::~enable_shared_from_this
enable_shared_from_this::operator=
Fonctions membres publiques
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Public member functions
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enable_shared_from_this::shared_from_this
 
Defined in header <memory>
template< class T > class enable_shared_from_this;
(depuis C++11)
std::enable_shared_from_this permet une t objet qui est actuellement géré par un std::shared_ptr nommé pt en toute sécurité de générer d'autres instances std::shared_ptr pt1, pt2, ... que tout l'actionnariat de t avec pt .
Original:
std::enable_shared_from_this allows an object t that is currently managed by a std::shared_ptr named pt to safely generate additional std::shared_ptr instances pt1, pt2, ... that all share ownership of t with pt.
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Héritant de std::enable_shared_from_this<T> fournit une T type avec une shared_from_this fonction membre. Si un objet de t T type est géré par un std::shared_ptr<T> nommé pt, puis T::shared_from_this appel renverra une nouvelle std::shared_ptr<T> qui partage la propriété avec des t pt .
Original:
Inheriting from std::enable_shared_from_this<T> provides a type T with a member function shared_from_this. If an object t of type T is managed by a std::shared_ptr<T> named pt, then calling T::shared_from_this will return a new std::shared_ptr<T> that shares ownership of t with pt.
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Notez que avant d'appeler shared_from_this sur une t objet, il doit y avoir un std::shared_ptr qui possède t .
Original:
Note that prior to calling shared_from_this on an object t, there must be a std::shared_ptr that owns t.
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A noter également que enable_shared_from_this offre une alternative à une expression comme std::shared_ptr<T>(this), qui est susceptible d'entraîner des this étant détruit plus d'une fois par plusieurs propriétaires qui ne sont pas au courant de eachother .
Original:
Also note that enable_shared_from_this provides an alternative to an expression like std::shared_ptr<T>(this), which is likely to result in this being destructed more than once by multiple owners that are unaware of eachother.
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Sommaire

[modifier] Fonctions membres

construit un objet enabled_shared_from_this
Original:
constructs an enabled_shared_from_this object
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(fonction membre protégée)
détruit un objet enable_shared_from_this
Original:
destroys an enable_shared_from_this object
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(fonction membre protégée)
renvoie une référence à this
Original:
returns a reference to this
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(fonction membre protégée)
retourne un shared_ptr qui partage la propriété de *this
Original:
returns a shared_ptr which shares ownership of *this
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(fonction membre publique)

[modifier] Notes

Une mise en œuvre commune pour enable_shared_from_this est de maintenir une référence faible (comme std::weak_ptr) à this. Les constructeurs de std::shared_ptr peut détecter la présence d'une base enable_shared_from_this et l'actionnariat des std::shared_ptrs existants, au lieu de supposer le pointeur n'est pas géré par quelqu'un d'autre .
Original:
A common implementation for enable_shared_from_this is to hold a weak reference (such as std::weak_ptr) to this. The constructors of std::shared_ptr can detect presence of a enable_shared_from_this base and share ownership with the existing std::shared_ptrs, instead of assuming the pointer is not managed by anyone else.
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[modifier] Exemple

#include <memory>
#include <iostream>
 
struct Good: std::enable_shared_from_this<Good>
{
    std::shared_ptr<Good> getptr() {
        return shared_from_this();
    }
};
 
struct Bad {
    std::shared_ptr<Bad> getptr() {
        return std::shared_ptr<Bad>(this);
    }
    ~Bad() { std::cout << "Bad::~Bad() called\n"; }
};
 
int main()
{
    // Good: the two shared_ptr's share the same object
    std::shared_ptr<Good> gp1(new Good);
    std::shared_ptr<Good> gp2 = gp1->getptr();
    std::cout << "gp2.use_count() = " << gp2.use_count() << '\n';
 
    // Bad, each shared_ptr thinks it's the only owner of the object
    std::shared_ptr<Bad> bp1(new Bad);
    std::shared_ptr<Bad> bp2 = bp1->getptr();
    std::cout << "bp2.use_count() = " << bp2.use_count() << '\n';
} // UB: double-delete of Bad

Résultat :

gp2.use_count() = 2
bp2.use_count() = 1
Bad::~Bad() called
Bad::~Bad() called
*** glibc detected *** ./test: double free or corruption

[modifier] Voir aussi

(C++11)
pointeur intelligent avec sémantique de propriétaires partagés
(classe générique) [edit]