std::weak_ptr<T>::owner_before

 

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std::weak_ptr

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weak_ptr::weak_ptr

weak_ptr::~weak_ptr

weak_ptr::operator=

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weak_ptr::reset

weak_ptr::swap

观察者

weak_ptr::use_count

weak_ptr::expired

weak_ptr::lock

weak_ptr::owner_before

weak_ptr::owner_hash (C++26)

weak_ptr::owner_equal (C++26)

非成员函数

swap(std::weak_ptr)

辅助类

atomic<std::weak_ptr> (C++20)

推导指南(C++17)

 

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

检查此 weak_ptr 是否在实现定义的基于所有者的顺序（与基于值的顺序相反）中先于 other。该顺序使得两个智能指针仅在它们都为空或它们都拥有同一个对象时才进行等效比较，即使通过 get() 获取的指针值不同（例如，因为它们指向同一个对象内的不同子对象）。

此顺序用于使共享和弱指针能够用作关联容器中的键，通常通过 std::owner_less。

参数

other

-

要比较的 std::shared_ptr 或 std::weak_ptr

返回值

如果 *this 先于 other，则为 true，否则为 false。常见的实现比较控制块的地址。

示例

运行此代码

#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';
}

输出

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

缺陷报告

以下更改行为的缺陷报告被追溯应用于之前发布的 C++ 标准。

DR	应用于	已发布的行为	正确的行为
LWG 2083	C++11	owner_before 未声明为 const	声明为 const
LWG 2942	C++11	owner_before 未声明为 noexcept	声明为noexcept

另请参见

owner_less (C++11)

提供基于所有权的混合类型排序，用于共享指针和弱指针 (类模板)