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std:: swap (std::weak_ptr)

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C++
Memory management library
( exposition only* )
Allocators
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Memory resources
Uninitialized storage (until C++20)
( until C++20* )
( until C++20* )
( until C++20* )

Garbage collector support (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
std::weak_ptr
定义于头文件 <memory>
template < class T >
void swap ( std:: weak_ptr < T > & lhs, std:: weak_ptr < T > & rhs ) noexcept ;
(C++11 起)

为 std:: weak_ptr 特化 std::swap 算法。交换 lhs 与 rhs 的内容。实际调用 lhs. swap ( rhs ) 。


目录

参数

lhs, rhs - 要交换内容的智能指针

返回值

(无)

复杂度

常量。

示例

运行此代码 
#include <iostream>
#include <memory>
#include <string>
struct Foo {
    Foo(int _val) : val(_val) { std::cout << "Foo...\n"; }
    ~Foo() { std::cout << "~Foo...\n"; }
    std::string print() { return std::to_string(val); }
    int val;
};
int main()
{
    std::shared_ptr<Foo> sp1 = std::make_shared<Foo>(100);
    std::shared_ptr<Foo> sp2 = std::make_shared<Foo>(200);
    std::weak_ptr<Foo> wp1 = sp1;
    std::weak_ptr<Foo> wp2 = sp2;
    auto print = [&]() {
        auto p1 = wp1.lock();
        auto p2 = wp2.lock();
        std::cout << " p1=" << (p1 ? p1->print() : "nullptr");
        std::cout << " p2=" << (p2 ? p2->print() : "nullptr") << '\n';  
    };
    print();
    std::swap(wp1, wp2);
    print();
    wp1.reset();
    print();
    std::swap(wp1, wp2);
    print();   
}

输出： 

Foo...
Foo...
 p1=100 p2=200
 p1=200 p2=100
 p1=nullptr p2=100
 p1=100 p2=nullptr
~Foo...
~Foo...

参见

交换两个对象的值
(函数模板)
交换内容
(公开成员函数)