C++ 只能指標迴圈引用簡單測試

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

using namespace std;

namespace
{
    class B;
    class A
    {
    public:
        std::shared_ptr<B> pb;
    };

    class B
    {
    public:
        std::shared_ptr<A> pa;
    };
}

int main()
{
    shared_ptr<A> *spa = nullptr;
    shared_ptr<B> *spb = nullptr;
    {
        shared_ptr<A> aobj(new A);
        shared_ptr<B> bobj(new B);
        spa = &aobj;
        spb = &bobj;
        aobj->pb = bobj;
        bobj->pa = aobj;
    }

    cout << "aobj use count:" << spa->use_count() << endl;
    cout << "bobj use count:" << spb->use_count() << endl;

    system("pause");
    return 0;
}

輸出:

aobj use count:1
bobj use count:1
請按任意鍵繼續. . .

可見，這樣的引用計數兩個物件各還有一個。將一個物件的share_ptr改成weak_ptr就可以了。