cpp/memory/weak ptr

is a smart pointer that holds a non-owning ("weak") reference to an object that is managed by std. It must be converted to std in order to access the referenced object.

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, is used to track the object, and it is converted to std to assume temporary ownership. If the original std is destroyed at this time, the object's lifetime is extended until the temporary std is destroyed as well.

Another use for is to break reference cycles formed by objects managed by std. If such cycle is orphaned (i.e., there are no outside shared pointers into the cycle), the reference counts cannot reach zero and the memory is leaked. To prevent this, one of the pointers in the cycle can be made weak.