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std::enable_shared_from_this

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std::enable_shared_from_this
Geschützt Member-Funktionen
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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=
Öffentliche Member-Funktionen
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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;
(seit C++11)
std::enable_shared_from_this kann ein Objekt t, die derzeit von einem std::shared_ptr pt sicher generieren zusätzliche std::shared_ptr Fällen pt1, pt2, ... dass alle Aktienbesitz t mit pt benannt ist geschafft .
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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Erben von std::enable_shared_from_this<T> stellt eine Art T mit einer Member-Funktion shared_from_this. Wenn ein Objekt t vom Typ T durch eine std::shared_ptr<T> Namen verwaltet wird pt, dann ruft T::shared_from_this wieder eine neue std::shared_ptr<T>, dass Aktien das Eigentum an t mit 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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Beachten Sie, dass vor dem Aufruf shared_from_this auf ein Objekt t, muss es eine std::shared_ptr die t besitzt sein .
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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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Beachten Sie auch, dass enable_shared_from_this eine Alternative zu einem Ausdruck wie std::shared_ptr<T>(this), die wahrscheinlich in this mehr als einmal zerstört durch mehrere Eigentümer, die nichts von einander sind das Ergebnis ist bietet .
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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Inhaltsverzeichnis

[Bearbeiten] Member-Funktionen

konstruiert eine enabled_shared_from_this Objekt
Original:
constructs an enabled_shared_from_this object
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(geschützt Member-Funktion)
zerstört eine enable_shared_from_this Objekt
Original:
destroys an enable_shared_from_this object
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(geschützt Member-Funktion)
gibt einen Verweis auf this
Original:
returns a reference to this
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(geschützt Member-Funktion)
gibt einen shared_ptr das Eigentum an *this Aktien
Original:
returns a shared_ptr which shares ownership of *this
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(öffentliche Elementfunktion)

[Bearbeiten] Notes

Eine gemeinsame Implementierung für enable_shared_from_this ist es, einen schwachen Verweis (z. B. std::weak_ptr) an this halten. Die Konstrukteure von std::shared_ptr kann die Anwesenheit eines enable_shared_from_this Basis und Aktienbesitz mit den bestehenden std::shared_ptrs erkennen, anstatt davon auszugehen, der Zeiger nicht von jemand anderem verwaltet .
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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[Bearbeiten] Beispiel

#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

Output:

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

[Bearbeiten] Siehe auch

smart pointer with shared object ownership semantics
(Klassen-Template) [edit]