[Boost-users] shared ptr + const_cast woes

From: Evan Drumwright (edrumwri_at_[hidden])
Date: 2006-06-28 09:28:17

Hi all,

I am having trouble with pointer ownership as a result of the const_cast 
operator.  In particular, for the code below, when a const_cast is used to 
create a const int pointer, the use count for x does not increase.  The 
result of this is that when x.pop_back() is called, y is no longer valid 
(though the use count for y remains 1).

The documentation for shared_ptr does not help here.  Any suggestions?

Thanks,
Evan

#include <vector>
#include <iostream>
#include <boost/shared_ptr.hpp>

int main()
{
        std::vector<boost::shared_ptr<int> > x;
        x.push_back(boost::shared_ptr<int>(new int));
        *x.front() = 4;
        std::cout << "use count: " << x.front().use_count() << std::endl;
        boost::shared_ptr<const int> y(const_cast<const int*>(x.front().get()));
        std::cout << "use count: " << x.front().use_count() << std::endl;
        std::cout << "use count: " << y.use_count() << std::endl;
        boost::shared_ptr<int> z(const_cast<int*>(y.get()));
        std::cout << "use count: " << z.use_count() << std::endl;
        std::cout << "use count: " << y.use_count() << std::endl;
        x.pop_back();
        std::cout << *y << std::endl;
}

Output:
use count: 1
use count: 1
use count: 1
use count: 1
use count: 1
0