The
weak_ptr class template stores a weak reference to an object
that is already managed by a
shared_ptr.To access the object, a
weak_ptr can be converted to a
shared_ptr using the member
function
lock.namespace std {
template<class T> class weak_ptr {
public:
using element_type = remove_extent_t<T>;
constexpr weak_ptr() noexcept;
template<class Y>
weak_ptr(const shared_ptr<Y>& r) noexcept;
weak_ptr(const weak_ptr& r) noexcept;
template<class Y>
weak_ptr(const weak_ptr<Y>& r) noexcept;
weak_ptr(weak_ptr&& r) noexcept;
template<class Y>
weak_ptr(weak_ptr<Y>&& r) noexcept;
~weak_ptr();
weak_ptr& operator=(const weak_ptr& r) noexcept;
template<class Y>
weak_ptr& operator=(const weak_ptr<Y>& r) noexcept;
template<class Y>
weak_ptr& operator=(const shared_ptr<Y>& r) noexcept;
weak_ptr& operator=(weak_ptr&& r) noexcept;
template<class Y>
weak_ptr& operator=(weak_ptr<Y>&& r) noexcept;
void swap(weak_ptr& r) noexcept;
void reset() noexcept;
long use_count() const noexcept;
bool expired() const noexcept;
shared_ptr<T> lock() const noexcept;
template<class U>
bool owner_before(const shared_ptr<U>& b) const noexcept;
template<class U>
bool owner_before(const weak_ptr<U>& b) const noexcept;
};
template<class T>
weak_ptr(shared_ptr<T>) -> weak_ptr<T>;
template<class T>
void swap(weak_ptr<T>& a, weak_ptr<T>& b) noexcept;
}