std::enable_shared_from_this
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Definido no cabeçalho <memory> | ||
template<class T >class enable_shared_from_this; | (desde C++11) | |
std::enable_shared_from_this permite uma t objeto que atualmente é administrada por um std::shared_ptr chamado pt com segurança gerar instâncias adicionais std::shared_ptrpt1, pt2, ... que todos acionária de t com 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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Herdando de
std::enable_shared_from_this<T> fornece uma T tipo com um shared_from_this função de membro. Se um objeto de tT tipo é gerido por um std::shared_ptr<T> chamado pt, em seguida, chamar T::shared_from_this irá retornar um novo std::shared_ptr<T> que compartilha a propriedade de t com 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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Note-se que antes da chamada
shared_from_this numa t objeto, deve haver um std::shared_ptr que possui 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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Observe também que
enable_shared_from_this fornece uma alternativa para uma expressão como std::shared_ptr<T>(this), o que provavelmente resultará em this sendo destruída mais de uma vez por vários proprietários que desconhecem 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.The text has been machine-translated via Google Translate.
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Índice |
[editar]Funções de membro
constrói um objeto 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. (protegido função de membro) | |
destrói um objeto 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. (protegido função de membro) | |
retorna uma referência para 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. (protegido função de membro) | |
retorna um shared_ptr que compartilha a propriedade de *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. (função pública membro) | |
[editar]Notas
Uma implementação comum para
enable_shared_from_this é manter uma referência fraca (como std::weak_ptr) para this. Os construtores de std::shared_ptr pode detectar a presença de uma base enable_shared_from_this e participação acionária com as std::shared_ptrs existentes, em vez de assumir o ponteiro não é gerenciado por outra pessoa.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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[editar]Exemplo
#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
Saída:
gp2.use_count() = 2 bp2.use_count() = 1 Bad::~Bad() called Bad::~Bad() called *** glibc detected *** ./test: double free or corruption
[editar]Veja também
(C++11) | smart pointer with shared object ownership semantics (modelo de classe) |
