Will it work to pass a reference to a base class to boost::thread, and have virtual functions in the derived class called?

Question

Suppose I have:

class Base
{
    public:

        void operator()()
        {
            this->run();
        }

        virtual void run () {}
}

class Derived : public Base
{
    public:

        virtual void run ()
        {
            // Will this be called when the boost::thread runs?
        }
}

int main()
{
    Base * b = new Derived();
    boost::thread t(*b); // <-- which "run()" function will be called - Base or Derived?
    t.join();
    delete b;
}

From my tests, I cannot get Derived::run() to be called. Am I doing something wrong, or is this impossible?

score 2 · Answer 1 · answered Nov 21 '12 at 06:04

By passing *b you actually "slice" Derived object, i.e. pass Base instance by value. You should pass Derived functor by pointer (or smart-pointer), like this:

thread t(&Derived::operator(), b); // boost::bind is used here implicitly

Of course, pay attention to the b lifetime.

score 0 · Accepted Answer · answered Nov 30 '12 at 13:23

0

@GManNickG's comment is the cleanest answer, and works perfectly. Boost.Ref is the way to go.

thread t(boost::ref(*b));

answered Nov 30 '12 at 13:23

Dan Nissenbaum

13,558
21
105
181

Will it work to pass a reference to a base class to boost::thread, and have virtual functions in the derived class called?

2 Answers2