関連ワード:  shared_ptr and weak_ptr    shared pointer and weak pointer in c++    c++ shared_ptr and weak_ptr    difference between shared_ptr and weak_ptr    unique_ptr shared_ptr and weak_ptr    weak_ptr vs shared_ptr    shared pointer weak pointer    std shared_ptr weak_ptr    difference between unique_ptr shared_ptr and weak_ptr    shared_ptr unique_ptr weak_ptr 区别