c++ shared_ptr的错误用法之cycle引用

最新推荐文章于 2025-03-07 18:58:05 发布

原创最新推荐文章于 2025-03-07 18:58:05 发布 · 610 阅读

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#c++ #shared-ptr #weak-ptr #析构函数

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本文探讨了在C++中使用shared_ptr时可能出现的循环引用问题，并提供了解决方案，即利用weak_ptr来打破循环引用，确保内存资源能够被正确回收。

#include <iostream>
#include <memory>
#include <string>
#include <vector>

using namespace std;

class Person
{
public:
    string name;
    shared_ptr<Person> monther;
    shared_ptr<Person> father;
    vector<shared_ptr<Person>> kids;
public:
    Person(const string& n,shared_ptr<Person> m = nullptr,shared_ptr<Person> f = nullptr):name(n),monther(m),father(f)
    {}
    ~Person()
    {
        cout << "delete " << name << endl;
        system("pause");
    }
};
shared_ptr<Person> initFamily(const string& name)
{
    shared_ptr<Person> mom(new Person(name + "'s monther"));
    shared_ptr<Person> dad(new Person(name + "'s father"));
    shared_ptr<Person> kid(new Person(name, mom, dad));
    mom->kids.push_back(kid);//++use_count;
    dad->kids.push_back(kid);//++use_count;
    return kid; //++use_count;
}//--use_count;
int main()
{
    shared_ptr<Person> kid = initFamily("Marco");//++use_count;
    cout << kid.use_count() << endl;
    //因shared_ptr形成cycle无法释放,故无法调用析构函数
    //下面的system("pause")则必须有,否则会一闪而过
    system("pause");
    return 0;
}

//解决办法:使用weak_ptr

#include <iostream>
#include <memory>
#include <string>
#include <vector>
using namespace std;

class Person
{
public:
    string name;
    shared_ptr<Person> monther;
    shared_ptr<Person> father;
    vector<weak_ptr<Person>> kids;
public:
    Person(const string& n, shared_ptr<Person> m = nullptr, shared_ptr<Person> f = nullptr):name(n),monther(m),father(f)
    {

    }
    ~Person()
    {
        cout << "detele " << name << endl;
    }
};
shared_ptr<Person> initFamily(const string& name)
{
    shared_ptr<Person> mom(new Person(name + "'s monther"));
    shared_ptr<Person> dad(new Person(name + "'s father"));
    shared_ptr<Person> kid(new Person(name, mom, dad));
    weak_ptr<Person> w_kid(kid);
    mom->kids.push_back(w_kid);
    dad->kids.push_back(w_kid);
    return kid;
}
int main()
{
    shared_ptr<Person> p = initFamily("Marco");
    cout << p.use_count() << endl;
    cout << "the kid is " << p->name << endl;
    cout << "the kid's monther " << p->monther->name << endl;
    cout << "the kid's father " << p->father->name << endl;
    for (auto &v : p->monther->kids)
        if (!v.expired())
            cout << v.lock()->name << endl;
    //析构函数会调用,则下面system("pause")不需要添加
    //另外通过命令行编译更直观
    //system("pause");
    return 0;
}