Exception propagation between threads in c++0x

I'am using gcc 4.5 and want to transfer an exception to a different thread: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2179.html

#include <stdexcept>
#include <iostream>
#include <thread>

struct Callable
{
    void operator()()
    {
        try
        {
            throw std::runtime_error("Bad things happened");
        }
        catch (...)
        {
            std::cout << "caught" << std::endl;
            e = std::current_exception();

            if (e == NULL)
            {
                std::cout << "inside NULL" << std::endl;
            }
        }
    }

    std::exception_ptr e;
};

int main()
{
    Callable c;

    std::thread t(c);
    t.join();

    if (c.e == NULL)
    {
        std::cout << "outside NULL" << std::endl;
    }
    else
 开发者_如何学编程   {
        std::rethrow_exception(c.e);
    }

    return 0;
}

The output I get:

caught
outside NULL

Seems e is not NULL inside the thread, but then outside it is?! What's wrong here?

---

I figured it out myself. std::thread makes a copy of struct Callable first...

The following works as expected:

#include <stdexcept>
#include <iostream>
#include <thread>

int main()
{
    std::exception_ptr e;

    std::thread t([&e]()
    {
        try
        {
            throw std::runtime_error("Bad things happened");
        }
        catch (...)
        {
            std::cout << "caught" << std::endl;
            e = std::current_exception();

            if (e == NULL)
            {
                std::cout << "inside NULL" << std::endl;
            }
        }
    });

    t.join();

    if (e == NULL)
    {
        std::cout << "outside NULL" << std::endl;
    }
    else
    {
        std::rethrow_exception(e);
    }

    return 0;
}