# std::weak_ptr<T>::use_count

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< cpp‎ | memory‎ | weak ptr

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 managed object at the instant of the call.

### Notes

expired() may be faster than `use_count()`. This function is inherently 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)

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