std::weak_ptr - Man Page

using element_type = typename remove_extent< _Tp >::type

template<typename _Yp , typename  = _Constructible<const shared_ptr<_Yp>&>> weak_ptr (const shared_ptr< _Yp > &__r) noexcept
weak_ptr (const weak_ptr &) noexcept=default
template<typename _Yp , typename  = _Constructible<const weak_ptr<_Yp>&>> weak_ptr (const weak_ptr< _Yp > &__r) noexcept
weak_ptr (weak_ptr &&) noexcept=default
template<typename _Yp , typename  = _Constructible<weak_ptr<_Yp>>> weak_ptr (weak_ptr< _Yp > &&__r) noexcept
bool expired () const noexcept
shared_ptr< _Tp > lock () const noexcept
template<typename _Yp > _Assignable< const shared_ptr< _Yp > & > operator= (const shared_ptr< _Yp > &__r) noexcept
weak_ptr & operator= (const weak_ptr &__r) noexcept=default
template<typename _Yp > _Assignable< const weak_ptr< _Yp > & > operator= (const weak_ptr< _Yp > &__r) noexcept
weak_ptr & operator= (weak_ptr &&__r) noexcept=default
template<typename _Yp > _Assignable< weak_ptr< _Yp > > operator= (weak_ptr< _Yp > &&__r) noexcept
template<typename _Tp1 > bool owner_before (const __shared_ptr< _Tp1, _Lp > &__rhs) const noexcept
template<typename _Tp1 > bool owner_before (const __weak_ptr< _Tp1, _Lp > &__rhs) const noexcept
void reset () noexcept
void swap (__weak_ptr &__s) noexcept
long use_count () const noexcept

(Note that these are not member symbols.)

template<typename _Tp > void swap (weak_ptr< _Tp > &__a, weak_ptr< _Tp > &__b) noexcept
Swap overload for weak_ptr.

class std::weak_ptr< _Tp >"A non-owning observer for a pointer owned by a shared_ptr.

Since

C++11

A weak_ptr provides a safe alternative to a raw pointer when you want a non-owning reference to an object that is managed by a shared_ptr.

Unlike a raw pointer, a weak_ptr can be converted to a new shared_ptr that shares ownership with every other shared_ptr that already owns the pointer. In other words you can upgrade from a non-owning 'weak' reference to an owning shared_ptr, without having access to any of the existing shared_ptr objects.

Also unlike a raw pointer, a weak_ptr does not become 'dangling' after the object it points to has been destroyed. Instead, a weak_ptr becomes expired and can no longer be converted to a shared_ptr that owns the freed pointer, so you cannot accidentally access the pointed-to object after it has been destroyed.