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std::weak_ptr::use_count(3) C++ Standard Libary std::weak_ptr::use_count(3) NAME std::weak_ptr::use_count - std::weak_ptr::use_count Synopsis 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. Parameters (none) Return value The number of shared_ptr instances sharing the ownership of the man- aged object at the instant of the call. Notes expired() may be faster than use_count(). This function is inher- ently racy, if the managed object is shared among threads that might be creating and destroying copies of the shared_ptr: then, the result is reliable only if it matches the number of copies uniquely owned by the calling thread, or zero; any other value may become stale before it can be used. Example // Run this code #include <iostream> #include <memory> std::weak_ptr<int> 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<int> 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<int>(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: ?? See also expired checks whether the referenced object was already deleted (public member function) http://cppreference.com 2022.07.31 std::weak_ptr::use_count(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | Output: | See also
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