std::weak_ptr::weak_ptr

 

C++

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Numerics library

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Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

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Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

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Date and time

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initializer_list (C++11)

bitset

hash (C++11)

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rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

Optional and any

optional (C++17)

any (C++17)

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pair

tuple (C++11)

apply (C++17)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

integer_sequence (C++14)

Swap, forward and move

swap

exchange (C++14)

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

Type operations

declval (C++11)

as_const (C++17)

 

Dynamic memory management

Smart pointers unique_ptr (C++11) shared_ptr (C++11) weak_ptr (C++11) auto_ptr (until C++17) owner_less (C++11) enable_shared_from_this (C++11) bad_weak_ptr (C++11) default_delete (C++11) Allocators allocator allocator_traits (C++11) allocator_arg_t (C++11) allocator_arg (C++11) uses_allocator (C++11) scoped_allocator_adaptor (C++11) pmr::polymorphic_allocator (C++17) Memory resources pmr::memory_resource (C++17) pmr::get_default_resource (C++17) pmr::set_default_resource (C++17) pmr::new_delete_resource (C++17) pmr::null_memory_resource (C++17) pmr::synchronized_pool_resource (C++17) pmr::unsynchronized_pool_resource (C++17) pmr::monotonic_buffer_resource (C++17) pmr::pool_options (C++17)

Uninitialized storage uninitialized_copy uninitialized_copy_n (C++11) uninitialized_fill uninitialized_fill_n raw_storage_iterator get_temporary_buffer return_temporary_buffer Garbage collection support declare_reachable (C++11) undeclare_reachable (C++11) declare_no_pointers (C++11) undeclare_no_pointers (C++11) pointer_safety (C++11) get_pointer_safety (C++11) Miscellaneous pointer_traits (C++11) addressof (C++11) align (C++11) C Library malloc calloc realloc free Low level memory management

 

std::weak_ptr

Member functions

weak_ptr::weak_ptr

weak_ptr::~weak_ptr

weak_ptr::operator=

Modifiers

weak_ptr::reset

weak_ptr::swap

Observers

weak_ptr::use_count

weak_ptr::expired

weak_ptr::lock

weak_ptr::owner_before

Non-member functions

std::swap

 

constexpr weak_ptr();	(1)	(since C++11)
weak_ptr( const weak_ptr& r );	(2)	(since C++11)
template< class Y > weak_ptr( const weak_ptr<Y>& r );	(2)	(since C++11)
template< class Y > weak_ptr( const std::shared_ptr<Y>& r );	(2)	(since C++11)
weak_ptr( weak_ptr&& r );	(3)	(since C++14)
template< class Y > weak_ptr( weak_ptr<Y>&& r );	(3)	(since C++14)

Constructs 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 the overload resolution unless 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". (since C++17)

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 the overload resolution unless Y* is implicitly convertible to T*

Parameters

r

-

a std::shared_ptr or std::weak_ptr that will be viewed by this std::weak_ptr

Exceptions

noexcept specification:  

noexcept

  

Example

Run this code

#include <memory>
#include <iostream>
 
struct Foo {};
 
int main()
{
   std::weak_ptr<Foo> w_ptr;
 
   {
      auto ptr = std::make_shared<Foo>();
      w_ptr = ptr;
      std::cout << "w_ptr.use_count() inside scope: " << w_ptr.use_count() << '\n';
   }
 
   std::cout << "w_ptr.use_count() out of scope: " << w_ptr.use_count() << '\n';
   std::cout << "w_ptr.expired() out of scope: " << std::boolalpha << w_ptr.expired() << '\n';
}

Output:

w_ptr.use_count() inside scope: 1
w_ptr.use_count() out of scope: 0
w_ptr.expired() out of scope: true

See also

operator=	assigns the weak_ptr (public member function)