September 2009 - Boost-users

[variant] how to in-place construct a variant
by Stefan Strasser 07 Sep '09

07 Sep '09

I can't figure out how to in-place construct the contents of a boost::variant. the error message using GCC is merely 516 kb in size. from the boost.variant tutoral: > By default, a variant default-constructs its first bounded type, so v initially contains int(0). If this is not desired, or if the first bounded type is not default-constructible, a variant can be constructed directly from any value convertible to one of its bounded types. from the synopsis: > template<typename T> variant(const T &); > template<typename T> variant & operator=(const T &); so why does the following fail: struct A : noncopyable{ A(int); A &operator=(int); }; struct B{}; int main(){ A a(5); //ok a=5; //ok variant<A,B> var(5); //error var=5; //error } both error messages complain about noncopyable being - noncopyable. compiler is gcc 4.3.2 thank you

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[Signals2] connecting signals and pointers to objects
by Julien Claassen 07 Sep '09

07 Sep '09

Dear all! I'm trying to let several threads communicate using Boost.Signals2. Now I have encountered problems when working with pointers to my function-objects. could you please read this example code and give me pointers to solving these issues. *** CODE EXTRACT *** typedef boost::signals2::signal<void (char)> sig_t; class Base { public: boost::signals2::connection connect(const sig_t::slot_type&); protected: sig_t its_signal; }; boost::signals2::connection Base::connect(const sig_t::slot_type& subscriber) { return its_signal.connect(subscriber); } class Derived : public Base { public: void run(); }; void Derived::run() { // do something its_signal(); // something more to be done } class Function_object { public: void slot_func(char); void run(); }; void Function_object::slot_func(char c) { cout << "Hurrah, I received char c: " << c << endl; } void Function_object::run() { Base* my_base_pointer = new Derived(); my_base_pointer->connect(boost::bind(&Function_object::slot_func, \ this)); // Here I get errors from the Boost.Signals2 headers my_base_pointer->run(); } int main() { Function_object fo; thread taskrunner(boost::bind(&Function_object::run, &fo)); taskrunner.join(); return 0; } *** END OF CODE *** I compiled it with: gcc (Debian 4.3.2-1.1) 4.3.2 On Debian Lenny Linux. It seems I could have a reference to my Base or Derived object, when doing the connection, but no pointer. The goal is to have more than one derived class from Base and store them all in some kind of container or simple array. I tried making a vector of references to the Base cass, but as it should be an abstract data type, it didn't work. I would appreciate any help with this! Kindest regards Julien -------- Music was my first love and it will be my last (John Miles) ======== FIND MY WEB-PROJECT AT: ======== http://ltsb.sourceforge.net the Linux TextBased Studio guide ======= AND MY PERSONAL PAGES AT: ======= http://www.juliencoder.de

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[Interprocess] Problem reading or wrting to shared memory
by Thomas.Schulze＠camco.de 07 Sep '09

07 Sep '09

Hello, I created a simple class for storing information in shared memory (native Windows): template< class data> struct SharedData { SharedData<data>(): value(0), var(0.0), written(1), read(0){ std::cout<<" Objekt bei "<<this<<" erzeugt!"<<std::endl;} int value; // just temporary, will be replaced by a more generic data type double var; // just temporary, will be replaced by a more generic data type boost::interprocess::interprocess_semaphore written,read; }; I created and mapped that memory like: boost::interprocess::windows_shared_memory shm (create_only,name, read_write,sizeof(SharedData<data>)); boost::interprocess::mapped_region region(shm,read_write); and assigned a new data structure to it's address with: pShared = new(region.get_address()) SharedData<data>(); with pShared: SharedData<data>* pShared; But when I try to access the stored data with this pointer my program simply quits. Probably I am making a really silly mistake? Kind regards, Thomas Tel.: +49 2762 408-0 Fax.: +49 2762 408-10 Internet: http://www.camcoaudio.com CAMCO Produktions- und Vertriebs-GmbH f�r Beschallungs- und Beleuchtungsanlagen - Fischpicke 5 - 57482 Wenden - Amtsgericht Siegen HRB 7075 - Gesch�ftsf�hrer: Joachim St�cker, Reiner Sassmann, Carsten Wegner

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[asio] SSL enabled http server3 example is blocking
by Mariusz Wojtysiak 07 Sep '09

07 Sep '09

Hello, I noticed, that my ssl server implemented with boost::asio, which use pool of 10 threads, use only first working thread. Even if I put long running operation (like: std::cin > c; ) in handler of ssl request, request from second client is hung until running operation finish in first thread. Similar problem was described in archived post: "[asio] SSL enabled http server3 example is blocking" http://groups.google.pl/group/boost-list/browse_frm/thread/c26432c90020e6d9… After a few hours of debugging asio, I found a reason: Class openssl_stream_service implement ssl operations (like async_handshake, async_write_some...) using strand_ member, which is type of io_service::strand. This causes that two ssl operations using the same ssl stream cannot be running in the same time. Here is piece of code, which I had on my server to handle client request: void Request::handleClientRequest() { boost::asio::async_read_until( m_sessionPtr->getSocket(), m_headerBuffer, '\n', boost::bind( &Request::readHeaderHandler, shared_from_this(), boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred ) ); } void Request::readHeaderHandler( const boost::system::error_code &error, std::size_t bytesTransferred ) { // long running operation char c; } Method readHeaderHandler() is called from io_service::strand, so during this long running operation any other requests from clients have to wait! Solution it simple and works fine for me: Instead of calling long operations directly in handler, post operation to io_service, like here: void Request::readHeaderHandler( const boost::system::error_code &error, std::size_t bytesTransferred ) { m_ioService.post( boost::bind ( &Request::executeCommandHandler::executeCommandHandler, shared_from_this() ) ); } void Request::executeCommandHandler() { // long running operation char c; } This way, readHeaderHandler() return immediately from current srand operation (so other client's request may be handled) and executeCommandHandler() is called a bit later.

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Looking for bgl-book.pdf
by Mathieu Malaterre 07 Sep '09

07 Sep '09

Hi there, Does anyone has a copy of bgl-book.pdf ? I am running a debian/linux system and there are no tool to decompress 'sit' file. Ref: http://www.informit.com/store/product.aspx?isbn=0201729148 or directl link: http://www.informit.com/content/images/0201729148/CDContents/0201729148_CD.… Thank you -- Mathieu

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[math] gamma distribution's quantile performance
by Christian Henning 06 Sep '09

06 Sep '09

Hi there, I have created a test which times the performance of boost::math::quantile( ... ) when using a gamma distribution. I ran it against source code we use here at work, for ages. It can be found here: http://people.sc.fsu.edu/~burkardt/cpp_src/dcdflib/dcdflib.html The old source code is about 2x times faster than the boost version. MS Visual Studio 2005: boost: 35.4sec att_bell:19sec Intel 11.1: boost: 21.4sec att_bell: 11.2sec Question is if there is a way to incorporate such a function into boost::math? As far, as I can tell the results are almost identical. Regards, Christian Here the code: #include <dcdflib.h> #include <boost/math/distributions/gamma.hpp> #include <boost/timer.hpp> double min_mean = 2000; // 2,000 double max_mean = 500000000; //500,000,000 double min_std = 10000; // 10,000 double max_std = 100000000; // 100,000,000 double min_max = 600000000; // 600,000,000 double max_max = 1000000000; // 1,000,000,000 const std::size_t max_year = 5000000; // 5,000,000 const double right = 0.999; const double left = 0.001; inline double get_rand() { return static_cast< double >( std::rand() ) / static_cast< double >( RAND_MAX ); } inline void boost_( boost::math::gamma_distribution<>& d, double q ) { double value = boost::math::quantile( d, q ); } inline void att_bell( double alpha, double beta, double q ) { double q_Minus1 = 1 - q; double value = 0.0; double bound = 0.0; int which = 2; int status = 0; cdfgam( &which , &q , &q_Minus1 , &value , &alpha , &beta , &status , &bound ); } int main() { // boost { std::srand( 0 ); boost::timer timer; for( std::size_t y = 0; y < max_year; ++y ) { if(( y % 100000 ) == 0 ) std::cout << y << std::endl; double mean = get_rand() * ( max_mean - min_mean ) + min_mean; double std = get_rand() * ( max_std - min_std ) + min_std; double alpha = mean * mean / std / std; // shape parameter double beta = mean / alpha; // scale parameter boost::math::gamma_distribution<> d( alpha, beta ); boost_( d, right ); boost_( d, left ); } std::cout << "Boost - Time elapsed: " << timer.elapsed() << " sec" << std::endl; } // att bell { std::srand( 0 ); boost::timer timer; for( std::size_t y = 0; y < max_year; ++y ) { if(( y % 100000 ) == 0 ) std::cout << y << std::endl; double mean = get_rand() * ( max_mean - min_mean ) + min_mean; double std = get_rand() * ( max_std - min_std ) + min_std; double alpha = mean * mean / std / std; // shape parameter double beta = mean / alpha; // scale parameter att_bell( alpha, beta, right ); att_bell( alpha, beta, left ); } std::cout << "ATT Bell - Time elapsed: " << timer.elapsed() << " sec" << std::endl; } return 0; }

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[ Boost.MPI ] : Spawning processes, Intercommunicators and send custom data-types ?
by Ashika Umanga Umagiliya 06 Sep '09

06 Sep '09

Greetings all, I use OpenMPI 1.3.3 and I tried to spawn child processes (using MPI_Comm_spawn) and send user-defined-datatypes across processes.The child processes should be ranked from 1-5 while the rank 0 is the manager processes (manager.cpp) . But I get rank 0 for manager process and the child processes also ranked starting from 0 (0-4) . So I cannot send data from manager process to first child processes (which suppose to be rank 1) Please give any suggestion to resolve this. thanks in advance, umanga manager.cpp (manager process which spawns child processes) - rank 0 ------------------------------------------------------------ int main(int argc,char *argv[]) { mpi::environment evn(argc,argv); mpi::communicator world; MPI_Comm everyone; //spawn 5 child processes. MPI_Comm_spawn("./worker", MPI_ARGV_NULL, 5, MPI_INFO_NULL, 0, MPI_COMM_SELF, &everyone, MPI_ERRCODES_IGNORE); intercommunicator intcomm(everyone,comm_duplicate); if(rank==0){ GPSPosition *obj=new GPSPosition(100,200,300); shared_ptr<Position> pos(new Position); pos->setVals(); obj->addP(pos); intcomm.send(0,100,obj); } return 0; } worker.cpp (child process)- should be ranked 1-5 ,but get 0-4 ----------------------------------------------------------------------------------- int main(int argc,char *argv[]) { mpi::environment evn(argc,argv); MPI_Comm parent; MPI_Comm_get_parent(&parent); intercommunicator incomm(parent,comm_duplicate); if(parent==MPI_COMM_NULL){ cout << "Intercommunicator is Null !"<<endl; }else{ int r=incomm.rank(); cout <<"Rank !"<<r<< endl; //get 0-4 if(r==1){ //try receiving data send from manager process } } return 0; }

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Member functions on boost::variant?
by Christopher Jefferson 06 Sep '09

06 Sep '09

Is there a nice way of calling a member function on a boost::variant (where I know said member function is implemented by all the types in the variant)? Chris

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boost::function/boost::bind compilation error
by Ahmed Badran 06 Sep '09

06 Sep '09

Hi, I was trying to use boost function/bind to bind the first argument of a member function that takes two arguments, when I got into a compilation error that I can't quite decipher or understand, below is a sample representation of the problem, and then there's the compilation error, am I doing something incorrectly here? I have tried removing the boost::mem_fn instantiation with no difference. #include <boost/function.hpp> #include <boost/bind.hpp> #include <boost/mem_fn.hpp> #include <iostream> using namespace std; using namespace boost; class my_class { public: void test(bool b) { cout << "got " << b << endl; } private: }; int main() { my_class c; boost::function1<void, bool> test_fn; boost::bind(&my_class::test, &c, _2); /* causes a compilation error */ test_fn = boost::bind<void>(boost::mem_fn(&my_class::test), &c, _2); /* works fine */ test_fn = bind1st(mem_fun(&my_class::test), &c); test_fn(true); test_fn(false); return 0; } /usr/boost/include/boost/bind/arg.hpp: In constructor 'boost::arg<I>::arg(const T&) [with T = boost::arg<2> ()(), int I = 1]': /usr/boost/include/boost/bind.hpp:292: instantiated from 'void boost::_bi::list2<A1, A2>::operator()(boost::_bi::type<void>, F&, A&, int) [with F = boost::_mfi::mf1<void, my_class, bool>, A = boost::_bi::list1<bool&>, A1 = boost::_bi::value<my_class*>, A2 = boost::arg<2>]' /usr/boost/include/boost/bind/bind_template.hpp:32: instantiated from 'typename boost::_bi::result_traits<R, F>::type boost::_bi::bind_t<R, F, L>::operator()(A1&) [with A1 = bool, R = void, F = boost::_mfi::mf1<void, my_class, bool>, L = boost::_bi::list2<boost::_bi::value<my_class*>, boost::arg<2> >]' /usr/boost/include/boost/function/function_template.hpp:152: instantiated from 'static void boost::detail::function::void_function_obj_invoker1<FunctionObj, R, T0>::invoke(boost::detail::function::function_buffer&, T0) [with FunctionObj = boost::_bi::bind_t<void, boost::_mfi::mf1<void, my_class, bool>, boost::_bi::list2<boost::_bi::value<my_class*>, boost::arg<2> > >, R = void, T0 = bool]' /usr/boost/include/boost/function/function_template.hpp:904: instantiated from 'void boost::function1<R, T1>::assign_to(Functor) [with Functor = boost::_bi::bind_t<void, boost::_mfi::mf1<void, my_class, bool>, boost::_bi::list2<boost::_bi::value<my_class*>, boost::arg<2> > >, R = void, T0 = bool]' /usr/boost/include/boost/function/function_template.hpp:785: instantiated from 'typename boost::enable_if_c<boost::type_traits::ice_not<boost::is_integral<Functor>::value>::value, boost::function1<R, T1>&>::type boost::function1<R, T1>::operator=(Functor) [with Functor = boost::_bi::bind_t<void, boost::_mfi::mf1<void, my_class, bool>, boost::_bi::list2<boost::_bi::value<my_class*>, boost::arg<2> > >, R = void, T0 = bool]' test.cpp:28: instantiated from here /usr/boost/include/boost/bind/arg.hpp:37: error: creating array with negative size ('-0x00000000000000001') Regards, Ahmed

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Boost.Variant: Passing visitor as a function argument
by Hawkes Steve-FSH016 06 Sep '09

06 Sep '09

Using the Boost.Variant library, I'm trying to pass a visitor as an argument to a class method (the class instance contains the objects to be visited), but I can't come up with a solution that compiles. For example: typedef std::pair<std::string, double> AttrDouble; typedef std::pair<std::string, int> AttrInt; typedef std::pair<std::string, std::string> AttrString; typedef boost::variant<AttrDouble, AttrInt, AttrString> Attr; typedef std::vector<Attr> AttrList; class Example { public: // Some code omitted for brevity -- void visit(boost::static_visitor<> const& visitor) { BOOST_FOREACH(Attr attr, i_attrList) { boost::apply_visitor(visitor, attr); } } private: AttrList i_attrList; }; The above gives compiler errors like this: boost-1_37/boost/variant/variant.hpp:806: error: no match for call to '(const boost::static_visitor<void>) (std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>&)' boost-1_37/boost/variant/variant.hpp:806: error: return-statement with a value, in function returning 'void' The problem seems to be that static_visitor doesn't actually contain op()--only the user-supplied derived class does. I've read through the Boost.Variant documentation repeatedly, looked at Boost.Variant source, and tried searching the Internet for examples, but I haven't found anything that shows how to do this, leading me to believe it may not be possible. Is there a way to pass a visitor as a function argument, or some alternative approach that allows visiting objects without having direct access to them (such as when they are class private data and the visitor is external to the class)? Thanks, Steve Hawkes

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