# std::experimental::weak_ptr<T>::weak_ptr

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< cpp‎ | experimental‎ | weak ptr

constexpr weak_ptr() noexcept; | (1) | (library fundamentals TS)
weak_ptr( const weak_ptr& r ) noexcept; | (2) | (library fundamentals TS)
template< class Y > weak_ptr( const weak_ptr<Y>& r ) noexcept; | (2) | (library fundamentals TS)
template< class Y > weak_ptr( const std::experimental::shared_ptr<Y>& r ) noexcept; | (2) | (library fundamentals TS)
weak_ptr( weak_ptr&& r ) noexcept; | (3) | (library fundamentals TS)
template< class Y > weak_ptr( weak_ptr<Y>&& r ) noexcept; | (3) | (library fundamentals TS)

Constructs a new `weak_ptr` that potentially shares an object with r.

1) Default constructor. Constructs empty `weak_ptr`.
2) Constructs new `weak_ptr` which shares an object managed by r. If r manages no object, *this manages no object too. The templated overloads don't participate in overload resolution unless either `Y*` is implicitly convertible to `T*`, or `Y` is the type "array of `N` `U`" for some type `U` and some number `N`, and `T` is the type "array of unknown bound of (possibly cv-qualified) `U`".
3) Move constructors. Moves a `weak_ptr` instance from r into *this. After this, r is empty and r.use_count() == 0. The templated overload doesn't participate in overload resolution unless either `Y*` is implicitly convertible to `T*`, or `Y` is the type "array of `N` `U`" for some type `U` and some number `N`, and `T` is the type "array of unknown bound of (possibly cv-qualified) `U`".

### Parameters

r | - | a std::experimental::shared_ptr or std::experimental::weak_ptr that will be viewed by this std::experimental::weak_ptr

### Exceptions

`noexcept` specification:
noexcept

### Example

| This section is incomplete Reason: no example

### See also

(constructor) | creates a new `weak_ptr` (public member function of `std::weak_ptr<T>`)
operator= | assigns the `weak_ptr` (public member function of `std::weak_ptr<T>`)

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