std::weak_ptr::weak_ptr
From cppreference.com
| 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*Contents |
[edit] Parameters
| r | - | a std::shared_ptr or std::weak_ptr that will be viewed by this std::weak_ptr |
[edit] Exceptions
noexcept specification:
noexcept
[edit] Notes
Because the default constructor is constexpr, static weak_ptrs are initialized as part of static non-local initialization, before any dynamic non-local initialization begins. This makes it safe to use a weak_ptr in a constructor of any static object.
[edit] 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
[edit] See also
assigns the weak_ptr (public member function) |