Get a pointer pointer for a smart pointer

Question

I have a smart pointer for an object, that I need to pass to a method, that only accepts a pointer pointer.

Here's an example, where the original smart pointer loses the ownership.

int main(int argc, char* argv[])
{
    std::unique_pointer<pcap_if_t> object;

    auto object_pointer = object.get();
    pcap_findalldevs(&object_pointer, ...); // The unique_ptr loses ownership after being passed to the function
}

How would I accomplish this, without the original smart pointer losing the pointer ownership?

EDIT:
The function I'm calling is pcap_findalldevs in libpcap. I'm afraid that the function might be the cause of losing ownership.
I have updated my code example to reflect the what I actually do.

Answer 1

Function which takes pointer to pointer usually does so because it might change it, and pcap_findalldevs is indeed does that. And that pointer should be released with call to pcap_freealldevs.

So your best bet is unique_ptr with custom deleter aquiring ownership from raw pointer:

struct pcap_deleter
{
    void operator()(pcap_if_t* ptr) 
    {
        pcap_freealldevs(ptr);
    }
};

//...
using pcap_ptr = std::unique_ptr<pcap_if_t, pcap_deleter> 
pcap_ptr get_devs() {
    pcap_if_t* object_pointer;
    pcap_findalldevs(&object_pointer, ...); 
    return pcap_ptr(object_pointer);
}

//...

auto object = get_devs();

Answer 2

Here's an example, where the original smart pointer loses the ownership.

Nope. The unique_ptr retains ownership after a call to get()

unique_ptr will lose ownership after a call to release()

reference: http://en.cppreference.com/w/cpp/memory/unique_ptr