std::enable_shared_from_this
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Elemento definito nell'header <memory> | ||
template<class T >class enable_shared_from_this; | (dal C++11) | |
std::enable_shared_from_this permette un t oggetto che è attualmente gestito da un std::shared_ptr nome pt per generare in modo sicuro altre istanze std::shared_ptrpt1, pt2, ... che tutti azionariato di t con 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.The text has been machine-translated via Google Translate.
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Eredità da
std::enable_shared_from_this<T> fornisce un T tipo con shared_from_this funzione membro. Se un oggetto di tT tipo è gestito da un std::shared_ptr<T> nome pt, quindi T::shared_from_this chiamata restituirà un nuovo std::shared_ptr<T> che la proprietà di parti t con 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.The text has been machine-translated via Google Translate.
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Notare che prima di chiamare
shared_from_this su un t oggetto, ci deve essere un std::shared_ptr che possiede t.Original:
Note that prior to calling
shared_from_this on an object t, there must be a std::shared_ptr that owns t.The text has been machine-translated via Google Translate.
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Si noti inoltre che
enable_shared_from_this fornisce un'alternativa a un'espressione come std::shared_ptr<T>(this), che è suscettibile di provocare this stati distrutti più di una volta da più proprietari che non sono a conoscenza della vicenda.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.The text has been machine-translated via Google Translate.
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Indice |
[modifica]Membri funzioni
costruisce un oggetto enabled_shared_from_thisOriginal: constructs an enabled_shared_from_this object The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (protetto funzione membro) | |
distrugge un oggetto enable_shared_from_thisOriginal: destroys an enable_shared_from_this object The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (protetto funzione membro) | |
restituisce un riferimento this Original: returns a reference to this The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (protetto funzione membro) | |
restituisce un shared_ptr che condivide la proprietà di *this Original: returns a shared_ptr which shares ownership of *this The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (metodo pubblico) | |
[modifica]Note
Un'implementazione comune per
enable_shared_from_this è quello di tenere un riferimento debole (come std::weak_ptr) a this. I costruttori di std::shared_ptr in grado di rilevare la presenza di una base enable_shared_from_this e gli assetti proprietari con i std::shared_ptrs esistenti, invece di assumere il puntatore non è gestito da nessun altro.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.The text has been machine-translated via Google Translate.
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[modifica]Esempio
#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(){returnstd::shared_ptr<Bad>(this);} ~Bad(){std::cout<<"Bad::~Bad() called\n";}}; int main(){// Good: the two shared_ptr's share the same objectstd::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 objectstd::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
[modifica]Vedi anche
(C++11) | smart pointer with shared object ownership semantics (classe template) |
