C++ shared_ptr的reset 用法

#include <iostream>
#include <memory>
class Tmp {
   public:
    Tmp(int a);
    ~Tmp();
    void print__a() { std::cout << "value = " << __a << std::endl; }

   private:
    int __a;
};

Tmp::Tmp(int a) : __a(a) {
    std::cout << "start" << __a << std::endl;
}

Tmp::~Tmp() {
    std::cout << "finish" << __a << std::endl;
}

int main() {
    std::shared_ptr<Tmp> sp;  // empty

    Tmp *xx = new Tmp(10);
    sp.reset(xx);  // takes ownership of pointer
    sp->print__a();

    std::cout << "============11" << std::endl;
    Tmp *tt = new Tmp(20);
    sp.reset(tt);  // takes ownership of pointer
    sp->print__a();
    std::cout << "============22" << std::endl;

    sp.reset();  // deletes managed object
    // sp->print__a();  //crash
    if (!sp.get()) {
        printf("empty\n");
    }
    return 0;
}

打印结果：

start10
value = 10
============11
start20
finish10
value = 20
============22
finish20
empty

• 所以reset()就是把shared_ptr赋空，reset(new Tmp(10)); 就是把shared_ptr 指向new Tmp(10)