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std::shared_ptr<T>:: swap

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void swap ( shared_ptr & r ) noexcept ;
(自 C++11 起)

交换 * this 与 r 所存储的指针值及所有权。引用计数（如果存在）不会进行调整。

参数

r - 用于交换内容的智能指针

返回值

(无)

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> p1 = std::make_shared<Foo>(100);
    std::shared_ptr<Foo> p2 = std::make_shared<Foo>(200);
    auto print = [&]()
    {
        std::cout << " p1=" << (p1 ? p1->print() : "nullptr");
        std::cout << " p2=" << (p2 ? p2->print() : "nullptr") << '\n';  
    };
    print();
    p1.swap(p2);
    print();
    p1.reset();
    print();
    p1.swap(p2);
    print();   
}

输出： 

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