std::weak_ptr
| Defined in header <memory>
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| template< class T > class weak_ptr; |
(since C++11) | |
std::weak_ptr is a smart pointer that holds a non-owning ("weak") reference to an object that is managed by std::shared_ptr. It must be converted to std::shared_ptr in order to access the referenced object.
std::weak_ptr models temporary ownership: when an object needs to be accessed only if it exists, and it may be deleted at any time by someone else, std::weak_ptr is used to track the object, and it is converted to std::shared_ptr to acquire temporary ownership. If the original std::shared_ptr is destroyed at this time, the object's lifetime is extended until the temporary std::shared_ptr is destroyed as well.
Another use for std::weak_ptr is to break reference cycles formed by objects managed by std::shared_ptr. If such cycle is orphaned (i.e., there are no outside shared pointers into the cycle), the shared_ptr reference counts cannot reach zero and the memory is leaked. To prevent this, one of the pointers in the cycle can be made weak.
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