Use weak pointers with shared objects

Strictly speaking, std::weak_ptr is not a smart pointer. Rather, it's an observer that operates in cooperation with shared_ptr. A weak_ptr object does not hold a pointer on its own.

There are circumstances where shared_ptr objects may create dangling pointers or race conditions, which could lead to memory leaks or other problems. The solution is to use weak_ptr objects with shared_ptr.

How to do it…

In this recipe, we examine the use of std::weak_ptr with std::shared_ptr, using a demonstration class that prints when its constructors and destructor are called.

• We start with the same class we've used to demonstrate shared_ptr and unique_ptr:

  struct Thing {
      string_view thname{ "unk" };
      Thing() {
          cout << format("default ctor: {}\n", thname);
      }
      Thing...