RetroSearch Browse

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://en.cppreference.com/w/cpp/algorithm/../ranges/../../cpp/memory/shared_ptr/owner_before.html below:

std::shared_ptr<T>::owner_before - cppreference.com

template< class Y > bool owner_before( const shared_ptr<Y>& other ) const noexcept;

template< class Y > bool owner_before( const std::weak_ptr<Y>& other ) const noexcept;

Checks whether this shared_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).

This ordering is used to make shared and weak pointers usable as keys in associative containers, typically through std::owner_less.

[edit] Parameters [edit] Return value

true if *this precedes other, false otherwise. Common implementations compare the addresses of the control blocks.

[edit] Example

#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

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior LWG 2873 C++11 owner_before was not declared noexcept declared noexcept [edit] See also provides mixed-type owner-based ordering of shared and weak pointers
(class template) [edit]

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4