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[Units] help with type-safe unit-specific conversions
by Justin Leonard 27 Jul '09

27 Jul '09

I have been playing with Boost.Units as part of a work project recently, and I am not sure what the best approach to "demarshalling" values in a specific unit. For example, I would like to do something like: using namespace boost::units; struct A { enum { feet, kilometers }; quantity<si::length> some_length; double foo(int type) { switch(type) { case feet: return quantity<feet>(some_length).value(); case kilometers: return quantity<kilometers>(some_length).value(); } } }; This approach is necessary for passing values to external libraries which do not (and probably will never) use Boost.Units. Is conversion_factor the best approach, or is there a way to achieve this implicitly using the type system? Thanks Justin

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filesystem: create_directory unexpected exception
by ciju john 27 Jul '09

27 Jul '09

Platform: Windows XP Pro Boost version: 1.38 1.39 (BoostPro binary release) try { boost::filesystem::create_directory ("C:\Program Files\hello123"); } catch (const boost::filesystem::basic_filesystem_error<char*>& ) { std::cerr << "Directory creation failed" << std::endl; } The above code crashes if user doesn't have root permission. I assume some exception is being thrown as catch (...) catches whatevers being thrown. The documentation says "Throws: basic_filesystem_error<Path> if Effects fails for any reason other than because the directory already exists." The requested directory "C:\Program Files\hello123" doesn't exist, so I should have caught a boost::filesystem::basic_filesystem_error. Is this a known issue or am I the only one seeing this? thanks, john

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New Boost.Build tutorial
by Boris Schaeling 27 Jul '09

27 Jul '09

As I started to use Boost.Build recently I wrote everything down what I learnt and what is partly missing in the documentation. The article can be found at: http://www.highscore.de/cpp/boostbuild/ There is also a reference of rules and features. If someone likes me to add more rules and features just send me a mail (including a description as I don't know all rules and features myself :). This will not only make the reference more complete. I might also learn something new which will help me to use Boost.Build more efficiently. By the way, there is also a section about best practices which I'm also interested in. Boris

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Why boost::asio doesn't work???
by Gotch＠ 27 Jul '09

27 Jul '09

I'm starting using Boost::Asio. I tried to write a simple class to send and receive asynchronously UDP datagrams, following the boost::asio tutorial. The class compiles fine, but it's not working and comes out with an exception about a mutex (which shouldn't be involved I guess). Basically there are two methods: one starts an async_receive_from and the other send packets asynchronously. I first start the receiver, then I try to send a packet to localhost (127.0.0.1). But nothing happens. Here is the code, maybe you may know what's wrong. With the following class the header: namespace msgSrv { class endPoint { public: asio::ip::udp::endpoint ep; endPoint(std::string ip, int port); }; class msgSrv { private: asio::ip::udp::socket *asioSocket; asio::io_service *asioIoService; int listenPort; boost::array<char, 1> rcvBuff; asio::ip::udp::endpoint lastRcvdPcktEndp; char * sbuff; public: boost::condition_variable cond; boost::mutex mut; msgSrv(int listenPort); virtual ~msgSrv(); void start(); void pckRcvd(const asio::error_code& error, std::size_t bytes_transferred); void sendTo(const char* buff, int len, endPoint ep); void sendHnd(const asio::error_code& error, std::size_t bytes_transferred); }; } the .cpp #include "msgSrv.h" namespace msgSrv { endPoint::endPoint(const std::string ip, int port) { asio::ip::address addr = asio::ip::address::from_string(ip); ep = asio::ip::udp::endpoint(addr, port); } msgSrv::msgSrv(int listenPort) { // TODO Auto-generated constructor stub this->listenPort = listenPort; try { asioIoService = new asio::io_service(); asioSocket = new asio::ip::udp::socket(*asioIoService, asio::ip::udp::endpoint(asio::ip::udp::v4(), listenPort)); //new asio::ip::udp::socket_(*asioIoService, udp::endpoint(udp::v4(), listenPort)); } catch (std::exception &e) { std::cerr << "Error initializing ioservice or socket:" << e.what(); } asioIoService->run(); } msgSrv::~msgSrv() { // TODO Auto-generated destructor stub delete asioIoService; delete asioSocket; } void msgSrv::start() { asioSocket->async_receive_from(asio::buffer(rcvBuff), lastRcvdPcktEndp, boost::bind(&msgSrv::pckRcvd, this, asio::placeholders::error, asio::placeholders::bytes_transferred)); } void msgSrv::pckRcvd(const asio::error_code& error, std::size_t bytes_transferred) { std::cout << "Rcvd! " << lastRcvdPcktEndp.address().to_string() << ":" << lastRcvdPcktEndp.port() << "\n"; } void msgSrv::sendTo(const char* buff, int len, endPoint ep) { sbuff = new char[len]; mempcpy(sbuff, buff, len); asioSocket->async_send_to(asio::buffer(sbuff, len), ep.ep, boost::bind( &msgSrv::sendHnd, this, asio::placeholders::error, asio::placeholders::bytes_transferred)); } void msgSrv::sendHnd(const asio::error_code& error, std::size_t bytes_transferred) { std::cout << "Snt!\n"; delete sbuff; } } and the following "main" file: int main() { msgSrv::msgSrv aa(4450); aa.start(); msgSrv::endPoint ep("127.0.0.1", 4450); std::string a("Prova!"); int len = a.length(); aa.sendTo(a.c_str(), len, ep); std::cout << "sent...\n"; std::cout << "notified...\n"; } all I get is: terminate called after throwing an instance of 'asio::system_error' what(): mutex: Invalid argument sent... notified... What's wrong?? I tried even to put a while(1) in the main, to see if something happens... I even tried to put a condition in the main that is unlocked by the receive handler... all remains locked... So what??? No idea!

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getting a handle to another connection?
by Ozgur Ozturk 27 Jul '09

27 Jul '09

Hi, I need to send ip information of a client to the other one (as they will connect to each other directly now). I used async echo server sample <http://www.boost.org/doc/libs/1_39_0/doc/html/boost_asio/example/echo/async…>as a starting point. I guess sessions are recorded in io_service instance, since in the server constructor when we create session, we pass io_service to it. session* new_session = new session(io_service_); Can I get information of connected sessions from io_service? (or any other recommendations on how to better design it?) To expand my question: I am implementing a chat server, but the chats will not go over the server (is it a bad idea?). many clients connects, I keep their status (online or not) in a database. when A wants to talk to B, I need to pass request to B, how can I get a handle to my connection to B while I am in the instance of session with A? I am still not sure I understand io_service concept. Is this proactor thing similar to observer pattern? When we pass io_service as a parameter to something, are we registering it to be observed in io_service? Thanks in advance, (*Thanks for all the previous answers too, *I have made significant progress...) Best regards, Ozgur (Oscar) Ozturk www.DrOzturk.com Phone: +1 (908) DROZGUR i.e, +1 (908) 376-9487

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Boost StateChart and Template parameters
by Etienne Philip Pretorius 27 Jul '09

27 Jul '09

Hello List, I would like to have a templated parse function within each of my states. Unfortunatly I am unable to successfully create a version that compiles, perhaps if someone could show how to get it to work. Here is the code: namespace xml { class prolog; template<typename T> class Entity { public: virtual boost::regex regex() const = 0; virtual void parse(T,T) = 0; }; class document : public boost::statechart::state_machine< document, prolog > { public: virtual ~document( ) {}; private: friend class prolog; static boost::regex character, white_space, name_start_character, name_character, name, names, nmtoken, nmtokens, comment, process_instruction_target, process_instruction, CDATA, equal, version_info, encoding_name, encoding_declaration, standalone_document_declaration, xml_declaration, prolog; protected: document( ) { initiate(); }; template<typename T> boost::regex regex( ) const { return state_cast<const Entity<T>&>().regex(); }; template<typename T> void parse( T begin, T end ) { return state_cast<const Entity<T>&>().parse(begin,end); } }; class prolog : public Entity ///<-----needs argument here but compains the 'prolog' is NOT a template , public boost::statechart::simple_state< prolog, document > { public: prolog( ) {}; ~prolog( ) {}; virtual boost::regex regex( ) const { return document::prolog;//FIXME...match element aswell }; virtual void parse( T begin, T end ) { }; private: protected: }; }; Any help on this will be appreciated. Thank you all. Etienne

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Database Template Libraries
by Etienne Philip Pretorius 27 Jul '09

27 Jul '09

Hello list, Just a quick question, are there boost libraries that are similar to this: http://dtemplatelib.sourceforge.net/ If not are there any plans for a generic boost database template library? Just Wandering. Etienne

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boost.datetime query
by Sean Farrow 27 Jul '09

27 Jul '09

Hi: I am working on a project whereby I need the date in the format yyyy-mm-dd (iso format). Am I write in thinking that the boost::Gregorian::to_Iso_string function will do this for me given a date as it's argument? I seem to have some discrepancies between the Embarcadero c++ 2009 implementation of that function and what I think should be happening having used the ms vc++ built version. Any help appreciated. Sean.

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test boost::try_mutex is locked or not
by Boost lzw 26 Jul '09

26 Jul '09

Hi everyone, I just did not find the right member function for it. Can anyone point out the correct function I should use? Thanks. CODE: ----------- boost::try_mutex resourceX; boost::try_mutex::scoped_lock lockX(resourceX); ... if(lockX.locked() == false) // compilation error do sth. ----------- The compiler complains that locked() is not a member function of boost::try_mutex Cheers, Robert

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Number of cores
by Ruediger Berlich 26 Jul '09

26 Jul '09

Hi there, is there a possibility in Boost to find out the number of processor(-core)s on a local system in a platform-independent way ? I'd like to start a corresponding number of threads. Thanks and Best Regards, Ruediger

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