C++ Programming :: Virtual Member Function


	Virtual Member Function Hi, I am using a class with operator() as threadfunc for Boost.Thread. I have inheritance used with those class but it does not work, see the example: // Snippet on #include <iostream> #include <vector> #include <boost/thread.hpp> class Bird { public: virtual void operator()() {std::cout << "a bird" << std::endl;} virtual ~Bird() {} }; class Swan : public Bird { public: virtual void operator()() {std::cout << "a swan" << std::endl;} }; int main() { Swan mySwan; Bird* myBird = &mySwan; Bird b = &mySwan; boost::thread thrd(b); thrd.join(); return 0; } // Snippet off I would like to see "a swan" displayed, but I get "a bird" instead... and for some reason I don't want to do that: boost::thread thrd(mySwan); As the member function is virtual, on call of operator () on the object b (which is a swan) I should see Swan::operator() called, no? What it it I don't understand here? Thanks and regards, JD On 25 May, 11:02, jean.daniel.mich@gmail.com wrote: - Hide quoted text - > Hi, > I am using a class with operator() as threadfunc for Boost.Thread. I > have inheritance used with those class but it does not work, see the > example: > // Snippet on > #include <iostream> > #include <vector> > #include <boost/thread.hpp> > class Bird > { > public: > virtual void operator()() {std::cout << "a bird" << std::endl;} > virtual ~Bird() {} > }; > class Swan : public Bird > { > public: > virtual void operator()() {std::cout << "a swan" << std::endl;} > }; > int main() > { > Swan mySwan; > Bird* myBird = &mySwan; > Bird b = &mySwan; > boost::thread thrd(b); when you dereference b, what you get is the Bird part of mySwan object. try instead boost::thread thrd(boost::bind(&Bird::operator(), b)); or if you have TR1 ::boost::thread thrd(std::tr1::bind(&Bird::operator(), b)); Hi jean.daniel.mich@gmail.com schreef: > I am using a class with operator() as threadfunc for Boost.Thread. I > have inheritance used with those class but it does not work, see the > example: [includes, class Bird, class Swan snipped] > int main() > { > Swan mySwan; > Bird* myBird = &mySwan; > Bird b = &mySwan; > boost::thread thrd(b); From the boost documentation: \| class thread : private boost::noncopyable // Exposition only \| { \| public: \| // construct/copy/destruct \| thread(); \| explicit thread(const boost::function0<void>&); \| ~thread(); and \| template<typename F> functionN(F f); \| Requires: F is a function object Callable from this. \| Postconditions: this targets a copy of f if f is nonempty, or \| this->empty() if f is empty. So effectively you create a boost::function0<Bird> object that _copies_ b (slicing!). You then create a boost::thread object from that. Avoid the copy by using an additional indirection, e.g. consider boost::ref : boost::thread thrd( boost::ref(*b) ); Markus Markus, dasjotre, Both you solutions work. Thanks a lot! JD