January 2015 - Boost-users - lists.boost.org

[Serialization] XML: float format is scientific instead of human-readable since Boost 1.57
by Frank Stähr 09 Feb '15

09 Feb '15

Hello Boost guys, when I switched from Boost 1.55 to 1.57 there was a change in the formation of floats and doubles for xml archives. Look at this example: #include <fstream> #include <boost/archive/xml_oarchive.hpp> class MyClass { friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int version) { ar & boost::serialization::make_nvp("accuracy", accuracy); } double accuracy = 0.03; }; int main() { MyClass obj; std::ofstream ofs("sample.xml"); boost::archive::xml_oarchive oa(ofs); oa & boost::serialization::make_nvp("myclass", obj); } I compiled it with VS 2013 for 32 bit. The output file has the line: <m_accuracy>2.99999999999999990e-002</m_accuracy> In Boost 1.55 it was much better human-readable: 0.03. Is this behaviour (this change) intended? In any case, what is the best way to format floats and doubles? (i. e. a manipulator for the ofstream?) Thanks, Frank -- Frank Stähr Technische Universität Berlin Communication Systems Group Sekr. EN1 Einsteinufer 17 10587 Berlin, Germany

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[msm] multi thread access
by Sam Fisher 05 Feb '15

05 Feb '15

Hi Christophe, Did you consider adding build-in multi-thread support? (via policies maybe?) For example, I can guaranteed that all access to sub-fsm within its handlers (process_event()) will be synchronized. The problem is, sub-fsm "knows" about its parent and internally communicates with it (forwarding events etc). I can't control it from my side. typical scenario: an action from sub-fsm struct A_Init { template <typename Evt, typename FSM, typename SourceState, typename TargetState> void operator()(Evt&, FSM& fsm, SourceState&, TargetState&) const { std::thread([=]() mutable { std::lock_guard<std::mutex> l(access); fsm.process_event(some_event()); }).detach(); } }; locking proccess_event() in sub-fsm doesn't help if it alters the root.

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[Variant] Assertion fails at variant/detail/visitation_impl.hpp:207
by Attila Rajmund Nohl 02 Feb '15

02 Feb '15

Hello! I'm using boost-1.55 on Linux. When I run a specific testcase, I get an abort at line 207 in the visitation_impl.hpp file. The comment says that "should never be here at runtime". Unfortunately I don't really understand under what circumstances could runtime end up here - could someone explain how? The variant has a recursive element, i.e. looks something like this: struct Resp; struct SR { } struct AR { std::vector<Resp> resp; } typedef variant< SR, recursive_wrapper<AR> > RMType; struct Resp { RMType rm; }

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boost::ptr_container library question ?
by Danny K 02 Feb '15

02 Feb '15

The ptr_container supports an overload for std::auto_ptr<U>. I was curious if there was a way to add the same functionality for std::unique_ptr<U>. ie an overload that allows a std::unique_ptr to be added to a ptr_vector for example?

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[type_erasure] Problem with iterators
by Marco Guazzone 31 Jan '15

31 Jan '15

Hi, I'm new to the Type Erasure library. I need to write a base class with type-erased forward iterators. To do so I've taken inspiration from the print_sequence.cpp example I've found in the Type Erasure source tree. At the end of the email there is the whole code of my tentative, called "erasure.cpp". Unfortunately, I've problems (presumably) with const iterators which cause the following compile error: $ g++ -Wall -Wextra -pedantic -std=c++11 -I$HOME/sys/src/git/boost -o erasure erasure.cpp -lm *** [begin error] *** In file included from /home/sguazt/sys/src/git/boost/boost/type_erasure/iterator.hpp:20:0, from erasure.cpp:2: /home/sguazt/sys/src/git/boost/boost/type_erasure/operators.hpp: In instantiation of ‘static R boost::type_erasure::dereferenceable<R, T>::apply(const T&) [with R = double&; T = __gnu_cxx::__normal_iterator<const double*, std::vector<double> >]’: /home/sguazt/sys/src/git/boost/boost/type_erasure/detail/instantiate.hpp:91:9: required from ‘static void boost::type_erasure::detail::instantiate_concept7::apply(Concept*, Map*) [with Concept = boost::mpl::vector<boost::type_erasure::forward_iterator<>, boost::type_erasure::same_type<boost::type_erasure::deduced<boost::type_erasure::iterator_value_type<boost::type_erasure::_self> >, double>, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>; Map = boost::mpl::map1<boost::mpl::pair<boost::type_erasure::_self, __gnu_cxx::__normal_iterator<const double*, std::vector<double> > > >]’ /home/sguazt/sys/src/git/boost/boost/type_erasure/any.hpp:225:13: required from ‘boost::type_erasure::any<Concept, T>::any(U&&) [with U = __gnu_cxx::__normal_iterator<const double*, std::vector<double> >&; Concept = boost::mpl::vector<boost::type_erasure::forward_iterator<>, boost::type_erasure::same_type<boost::type_erasure::deduced<boost::type_erasure::iterator_value_type<boost::type_erasure::_self> >, double>, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>; T = boost::type_erasure::_self]’ erasure.cpp:36:40: required from ‘std::vector<_RealType> base<T>::foo(IterT, IterT) [with IterT = __gnu_cxx::__normal_iterator<const double*, std::vector<double> >; T = double]’ erasure.cpp:77:73: required from here /home/sguazt/sys/src/git/boost/boost/type_erasure/operators.hpp:134:44: error: invalid initialization of reference of type ‘double&’ from expression of type ‘const double’ static R apply(const T& arg) { return *arg; } *** [/end error] *** The GCC version is 4.9.2. Here below is the content of "erasure.cpp". If I comment lines below the comment "THE FOLLOWING WON'T COMPILE" I get no error. So the problem is due to the use of cbegin/cend. *** [erasure.cpp] *** #include <boost/type_erasure/any.hpp> #include <boost/type_erasure/iterator.hpp> #include <boost/type_erasure/operators.hpp> #include <boost/type_erasure/same_type.hpp> #include <boost/mpl/vector.hpp> #include <boost/smart_ptr.hpp> #include <cmath> #include <cstddef> #include <iostream> #include <iterator> #include <vector> namespace mpl = boost::mpl; namespace te = boost::type_erasure; template <typename T> using fwd_iter_impl_t = te::any< mpl::vector< te::forward_iterator<>, te::same_type<te::forward_iterator<>::value_type,T>>>; template <typename T> class base { protected: typedef fwd_iter_impl_t<T> fwd_iter_type; public: virtual ~base() { } template <typename IterT> std::vector<T> foo(IterT first, IterT last) { return this->do_foo(first, last); } private: virtual std::vector<T> do_foo(fwd_iter_type first, fwd_iter_type last) = 0; }; // base template <typename T> class derived: public base<T> { private: typedef typename base<T>::fwd_iter_type fwd_iter_type; std::vector<T> do_foo(fwd_iter_type first, fwd_iter_type last) { const std::ptrdiff_t n = std::distance(first, last); std::vector<T> res(n); for (std::size_t i = 0; first != last; ++first, ++i) { res[i] = std::pow(*first,i)/n; } return res; } }; // derived int main() { std::vector<double> dv; dv.push_back(5); dv.push_back(8); dv.push_back(11); boost::scoped_ptr< base<double> > p_base(new derived<double>()); // begin/end const std::vector<double> foos = p_base->foo(dv.begin(), dv.end()); for (std::size_t i = 0; i < foos.size(); ++i) { std::cout << "foos[" << i << "]: " << foos[i] << std::endl; } //--- THE FOLLOWING WON'T COMPILE // cbegin/cend const std::vector<double> cfoos = p_base->foo(dv.cbegin(), dv.cend()); for (std::size_t i = 0; i < cfoos.size(); ++i) { std::cout << "cfoos[" << i << "]: " << cfoos[i] << std::endl; } } *** [/erasure.cpp] *** Thank you very much for your help. Best, -- Marco

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[Asio] Handlers of asycn_send_to are called in which order?
by Attila Rajmund Nohl 30 Jan '15

30 Jan '15

Hello! My code sends UDP packets using async_send_to. If all packets are successfully sent, are their handlers called in the same order as the async_send_to calls happened? I mean if my code looks something like this: socket.async_send_to(buffer1, destination, handler1); socket.async_send_to(buffer2, destination, handler2); Is it guaranteed that handler2 is always called after handler1?

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[iostreams] Devices and WOULD_BLOCK
by David Hawkins 30 Jan '15

30 Jan '15

Hi all, Boost newcomer here ... I have an application where I need to encode/decode a serialized data stream. I have used Boost.Iostreams filtering_stream filter to implement encoding and decoding function of each layer. The device interface is via a USB device, eg., think USB-to-Serial device, but without the classic Virtual COM Port or ttyUSB0 layer available. For example, the FTDI FT232H USB-to-MPSSE interface is a suitable cable http://www.ftdichip.com/Products/Cables/USBMPSSE.htm The cable can be used to implement either JTAG or SPI mode access (the mode selection introduces different filters into the filtering_stream stack). I have the filters working, and am working on getting a device working. Rather than deal with the details of the final hardware, I figured I'd simplify the design by creating a client/server design via sockets; the client code matches what I would use with real hardware, while the server code emulates the hardware. I started with this example for a socket device http://stackoverflow.com/questions/12023166/is-there-a-boostiostreams-bidir… The "problem" with the protocol I need to decode (which I have no choice to change) is that the data stream possibly contains escaped characters, so there is no way to know the read data length at the socket layer - its up to the filtering_stream layers to request data from the device layer until a complete packet is decoded. This all sounds good in theory, but in practice the filter layers attempt to read in blocks, and the read size is often larger than the read data that the device layer will supply. This lead to higher-level layers blocking in read(). I figured (perhaps incorrectly) that I could deal with this using non-blocking socket reads. After reading Boost.Iostreams non-blocking support in Section 3.6 http://www.boost.org/doc/libs/1_57_0/libs/iostreams/doc/index.html http://www.boost.org/doc/libs/1_57_0/libs/iostreams/doc/guide/asynchronous.… I modified the socket device example in the link above to; * put the socket in non-blocking mode before constructing the device * change the device 'read' procedure to return WOULD_BLOCK rather than throw an exception This does not work, and its not due to the filter layers. There is an issue with the device layer. Here's the issue ... given a design with a filtering_stream created only with a socket_device and no filters, if I trace the code in a debugger (Boost 1.57.0 source, Visual Studio 2012 under Win7), the socket_device read method call return sequence is boost/iostreams/read.hpp - read_device_impl read template at line 187 - read at line 52 boost/iostreams/detail/adapter/concept_adapter.hpp - device_wrapper_impl read at line 169 - read at line 77 boost/iostreams/detail/streambuf/indirect_streambuf.hpp - line 258 i.e., this source file https://github.com/boostorg/iostreams/blob/master/include/boost/iostreams/d… and this particular block of code // Read from source. std::streamsize chars = obj().read(buf.data() + pback_size_, buf.size() - pback_size_, next_); if (chars == -1) { this->set_true_eof(true); chars = 0; } setg(eback(), gptr(), buf.data() + pback_size_ + chars); The code tests for EOF (-1), but not WOULD_BLOCK (-2), so after this point, since chars is -2, things go bad. So I guess my question now is; Have I just bumped into the as-yet-unsupported part of Boost.Iostreams support for asynchronous I/O? Cheers, Dave PS. I can post example code if anyone wants to trace the code for themselves, I just figured I'd post the question to start with.

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Joining boost::asio::strands
by Cesar Mello 29 Jan '15

29 Jan '15

Hi, After spawning several paralell jobs through calls to boost::asio::spawn inside a loop, is there an easy way to wait for all of them to finish? I would like to join them to aggregate the results. Please can you give me any clue? Thank you a lot! Best regards Cesar

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ProgramOptions: explicit empty string argument
by Akim Demaille 29 Jan '15

29 Jan '15

Hi, I would like to be able to support an empty optional argument for long options. This is something that is supported by gnu getopt_long and argp. Consider for instance a simplified version of the first simple example program: #include <iostream> #include <boost/program_options.hpp> int main(int ac, char* av[]) { namespace po = boost::program_options; using namespace std; po::options_description desc("Allowed options"); desc.add_options() ("help", "produce help message") ("compression", po::value<string>()->implicit_value(""), "set compression level") ; po::variables_map vm; po::store(po::parse_command_line(ac, av, desc), vm); po::notify(vm); if (vm.count("help")) cout << desc << "\n"; else if (vm.count("compression")) cout << "Compression level was set to " << vm["compression"].as<string>() << ".\n"; else cout << "Compression level was not set.\n"; } when I run it, in "typical cases", I have: $ ./a.out Compression level was not set. $ ./a.out --compression=foo Compression level was set to foo. $ ./a.out --compression foo Compression level was set to foo. $ ./a.out --compression Compression level was set to . all of this is fine. However, how can I explicitly pass the empty string? $ ./a.out --compression= libc++abi.dylib: terminating with uncaught exception of type boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::program_options::invalid_command_line_syntax> >: the argument for option '--compression' should follow immediately after the equal sign zsh: abort ./a.out --compression= Of course I could simply to my user that there is a special token, say '-', that means "empty", but it is still more complex than simply accepting the empty string to mean the empty string. Thanks! (There are some stack overflow questions, but they do not address this particular point, --foo='').

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[interprocess] Bizarro File Names (Windows)
by Aaron_Wright＠selinc.com 28 Jan '15

28 Jan '15

I have a service that is running in Windows Server 2008 R2 SP1 that uses shared memory. It runs fine for a month or so, but then stops working correctly. When I check the C:\ProgramData\boost_interprocess\*\ folder, I get a bunch of weird file names, such as: 88C861CD6DE2CF01EBA2F0CC1200D001A4070000EBFFFFFF 88C861CD6DE2CF01EBA2F0CC1200D001A4070000ECFFFFFF 88C861CD6DE2CF01EBA2F0CC1200D001A4070000EDFFFFFF 88C861CD6DE2CF01EBA2F0CC1200D001A4070000EEFFFFFF 88C861CD6DE2CF01EBA2F0CC1200D001A4070000EFFFFFFF 88C861CD6DE2CF01EBA2F0CC1200D001A4070000F0FFFFFF 88C861CD6DE2CF01EBA2F0CC1200D001A4070000F1FFFFFF 88C861CD6DE2CF01EBA2F0CC1200D001A4070000F2FFFFFF 88C861CD6DE2CF014B04F3CC1200D001A40700000AFFFFFF 88C861CD6DE2CF014B04F3CC1200D001A40700000BFFFFFF 88C861CD6DE2CF014B04F3CC1200D001A40700000CFFFFFF 88C861CD6DE2CF014B04F3CC1200D001A40700000DFFFFFF ... (and so on) These are not even close to the names that are supposed to be used. They seem to increment a bit, then shift slightly, and start incrementing again. When I restart the service I get similar named files and patterns, and my services crashes because it can't grow shared memory (presumably because the file names are not correct). I have to restart the box in order to get the correct behavior. Has anyone seen this behavior before? --------------------------------------------------------- Aaron Wright

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