std::weak_ptr::weak_ptr

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*.

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

#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';
}

Output:

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

std::weak_ptr::weak_ptr

Parameters

Exceptions

Example

See also