How to check if weak_ptr is empty (non-assigned)?

Question

Is there a way to distinguish between an assigned (possibly expired) weak_ptr and a non-assigned one.

weak_ptr w1;
weak_ptr w2 = ...;
         


        

Answer 1

Using std::weak_ptr::expired()

#include 
#include 

//declare a weak pointer
std::weak_ptr gw;

void f()
{
    //check if expired
    if (!gw.expired()) {
        std::cout << "pointer is valid\n";
    }
    else {
        std::cout << "pointer  is expired\n";
    }
}

int main()
{
    f();
    {
        auto cre = std::make_shared(89);
        gw = cre;
        f();
    } 

    f();
}

Output

pointer  is expired
pointer is valid
pointer  is expired
Program ended with exit code: 0