std::weak_ptr::use_count - cppreference.com (original) (raw)

| long use_count() const noexcept; | | (since C++11) | | --------------------------------- | | ------------- |

Returns the number of shared_ptr instances that share ownership of the managed object, or ​0​ if the managed object has already been deleted, i.e. *this is empty.

[edit] Parameters

(none)

[edit] Return value

The number of shared_ptr instances sharing the ownership of the managed object at the instant of the call.

[edit] Notes

The usage and behavior of this function are similar to std::shared_ptr::use_count, but it returns a different count.

[edit] Example

#include #include   std::weak_ptr gwp;   void observe_gwp() { std::cout << "use_count(): " << gwp.use_count() << "\t id: "; if (auto sp = gwp.lock()) std::cout << *sp << '\n'; else std::cout << "??\n"; }   void share_recursively(std::shared_ptr sp, int depth) { observe_gwp(); // : 2 3 4 if (1 < depth) share_recursively(sp, depth - 1); observe_gwp(); // : 4 3 2 }   int main() { observe_gwp(); { auto sp = std::make_shared(42); gwp = sp; observe_gwp(); // : 1 share_recursively(sp, 3); // : 2 3 4 4 3 2 observe_gwp(); // : 1 } observe_gwp(); // : 0 }

Output:

use_count(): 0 id: ?? use_count(): 1 id: 42 use_count(): 2 id: 42 use_count(): 3 id: 42 use_count(): 4 id: 42 use_count(): 4 id: 42 use_count(): 3 id: 42 use_count(): 2 id: 42 use_count(): 1 id: 42 use_count(): 0 id: ??

[edit] See also

| | checks whether the referenced object was already deleted (public member function) [edit] | | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |