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std::weak_ptr::owner_before

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< cpp‎ | memory‎ | weak ptr

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template< class T >
bool owner_before( const weak_ptr<T>& other) const;
template< class T >
bool owner_before( const std::shared_ptr<T>& other) const;
Controlla se questo weak_ptr precede other in attuazione definito proprietario-based (in alternativa al fair-based) ordine. L'ordine è tale che due puntatori intelligenti confronta equivalente solo se sono entrambi vuoti o se sia proprio lo stesso oggetto, anche se i valori dei puntatori ottenuti get () sono differenti (ad esempio perché puntare sottooggetti diverse all'interno della stessa oggetto)
Original:
Checks whether this weak_ptr precedes other in implementation defined owner-based (as opposed to value-based) order. The order is such that two smart pointers compare equivalent only if they are both empty or if they both own the same object, even if the values of the pointers obtained by get() are different (e.g. because they point at different subobjects within the same object)
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Questo ordinamento è usato per fare in comune e puntatori deboli utilizzabili come chiavi in ​​contenitori associativi, di norma nell'ambito std::owner_less.
Original:
This ordering is used to make shared and weak pointers usable as keys in associative containers, typically through std::owner_less.
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Indice

[modifica] Parametri

other -
il std::shared_ptr o std::weak_ptr da confrontare
Original:
the std::shared_ptr or std::weak_ptr to be compared
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[modifica] Valore di ritorno

true se *this precede other, false altrimenti. Implementazioni comuni confrontare gli indirizzi dei blocchi di controllo.
Original:
true if *this precedes other, false otherwise. Common implementations compare the addresses of the control blocks.
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[modifica] Esempio

#include <iostream>
#include <memory>
 
struct Foo {
    int n1;
    int n2; 
    Foo(int a, int b) : n1(a), n2(b) {}
};
int main()
{   
    auto p1 = std::make_shared<Foo>(1, 2);
    std::shared_ptr<int> p2(p1, &p1->n1);
    std::shared_ptr<int> p3(p1, &p1->n2);
 
    std::cout << std::boolalpha
              << "p2 < p3 " << (p2 < p3) << '\n'
              << "p3 < p2 " << (p3 < p2) << '\n'
              << "p2.owner_before(p3) " << p2.owner_before(p3) << '\n'
              << "p3.owner_before(p2) " << p3.owner_before(p2) << '\n';
 
    std::weak_ptr<int> w2(p2);
    std::weak_ptr<int> w3(p3);
    std::cout 
//              << "w2 < w3 " << (w2 < w3) << '\n'  // won't compile 
//              << "w3 < w2 " << (w3 < w2) << '\n'  // won't compile
              << "w2.owner_before(w3) " << w2.owner_before(w3) << '\n'
              << "w3.owner_before(w2) " << w3.owner_before(w2) << '\n';
 
}

Output: 

p2 < p3 true
p3 < p2 false
p2.owner_before(p3) false
p3.owner_before(p2) false
w2.owner_before(w3) false
w3.owner_before(w2) false

[modifica] Vedi anche

(C++11)
fornisce di tipo misto proprietario basato su ordinamento di puntatori condivisi e debole
Original:
provides mixed-type owner-based ordering of shared and weak pointers
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(classe template) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/memory/weak_ptr/owner_before&oldid=17044"