std::weak_ptr<T>::use_count

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.

# Declarations

long use_count() const noexcept;

(since C++11)

# Return value

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

# Notes

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

# Example

#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
}

# See also

expired