What is the difference between std::weak_ptr and std::shared_ptr?

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**shared_ptr** — owns object. **weak_ptr** — observes without owning. **std::shared_ptr:** - Owns object. - Increments reference count. - Keeps object alive. ```cpp auto sptr = std::make_shared(10); // Object stays alive while shared_ptr exists ``` **std::weak_ptr:** - Non-owning reference. - Does NOT increment count. - Does NOT keep object alive. - Must lock to access. ```cpp std::weak_ptr wptr = sptr; // Check if object still exists if (auto locked = wptr.lock()) { // Object is alive, use *locked } else { // Object was destroyed } ``` **Use case — breaking circular reference:** ```cpp class Node; class Node { public: std::shared_ptr next; std::weak_ptr prev; // weak to break cycle }; ``` **Without weak_ptr:** - Circular reference → memory leak. - Reference count never reaches 0.

C++: What is the difference between std::weak_ptr and std::shared_ptr?