I/O on object pointers.

[judge]

I have written I/O operations for pointers to objects of class Foo.

typedef Foo *FooPtr;

std::istream &operator>>(std::istream &is, FooPtr &foo_ptr)
{
    bool is_null;
    if (!(is >> is_null))
        return is;

    if (is_null)
    {
        foo_ptr = 0;
        return is;
    }

    foo_ptr = new Foo();
    return is >> *foo_ptr;
}

std::ostream &operator<<(std::istream &os, FooPtr foo_ptr)
{
    return os << (foo_ptr != 0) << " " << (foo_ptr ? *foo_ptr : "");
}

How do I improve these functions so that two equal pointers written to a stream can be later read as two equal pointers?