Create a boost::shared_ptr to an existing variable

Question

I have an existing variable, e.g.

int a = 3;

How can I now create a boost::shared_ptr to a? For example:

Answer 1

What you wrote won't work because the constructor of shared_ptr you're looking for is explicit, so you'd need to write it like so

boost::shared_ptr a_ptr(&a); // Don't do that!

The problem with that however, is that delete will be called on the stored value of a_ptr. Since in your example a has automatic storage duration, this is very bad. So we pass in a custom deleter too:

boost::shared_ptr a_ptr(&a, noop_deleter);

An implementation of noop_deleter for C++11:

auto noop_deleter = [](int*) {};

C++03 version:

// Can't be put in local scope
struct {
    void
    operator()(int*) const
    {}
} noop_deleter;