April 2016 - Boost-users - lists.boost.org

measuring distance between a point and a segment
by Juliette Pera 22 Apr '16

22 Apr '16

Dear all, I am currently trying to use the boost library in order to measure the shortest distance between a point and a list of segments. I am declaring a segment to which I append the two points of my segment and the I calculate the distance from my point P to the segment. xsegment_t segment; geom::append(segment,geom::make_point(A[0],A[1])); geom::append(segment,geom::make_point(B[0],B[1])); double distance2 = geom::distance(segment,geom::make_point(P[0],P[1])); The issue is that I measure every time the same distance even if the segment is different. Does anyone knows from where that issue can come from? Thank you in advance, Juliette Pera

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[units] division with absolute temperature
by João Leal 19 Apr '16

19 Apr '16

Hello, I'm trying to use absolute temperature in some expressions. Unfortunately I'm having some issues with the compilation. For instance, if I divide an absolute temperature by itself I would expect to get 1 dimensionless, however that will cause a compilation error. #include <iostream> #include <boost/units/absolute.hpp> #include <boost/units/io.hpp> #include <boost/units/quantity.hpp> #include <boost/units/systems/si.hpp> #include <boost/units/systems/si/io.hpp> int main(int argc, char** argv) { using namespace boost::units; quantity<si::temperature> rT(273.15 * si::kelvin); // relative temperature quantity<si::dimensionless> v; v = rT / rT; std::cout << v << std::endl; // 1 dimensionless quantity<absolute<si::temperature> > aT(273.15 * absolute<si::temperature>()); // absolute temperature //v = aT / aT; // uncommenting this line will cause compilation errors //std::cout << v << std::endl; // 1 dimensionless return 0; } If I uncomment the line with v = aT / aT, in ubuntu 15.10 with boost 1.58 and gcc 5.2.1, I get the error: (...) /usr/include/boost/units/operators.hpp:81:5: error: no match for ‘operator/’ (operand types are ‘boost::units::absolute<boost::units::unit<boost::units::list<boost::units::dim<boost::units::temperature_base_dimension, boost::units::static_rational<1l> >, boost::units::dimensionless_type>, boost::units::homogeneous_system<boost::units::list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10l, boost::units::static_rational<3l> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > > > >’ and ‘boost::units::absolute<boost::units::unit<boost::units::list<boost::units::dim<boost::units::temperature_base_dimension, boost::units::static_rational<1l> >, boost::units::dimensionless_type>, boost::units::homogeneous_system<boost::units::list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10l, boost::units::static_rational<3l> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > > > >’) BOOST_TYPEOF_NESTED_TYPEDEF_TPL(nested, (typeof_::make<X>()/typeof_::make<Y>())) (...) I could add something like namespace boost { namespace units { template<class Unit, class X, class Y> struct divide_typeof_helper<quantity<absolute<Unit>, X>, quantity<absolute<Unit>, Y> > { typedef typename divide_typeof_helper<X, Y>::type value_type; typedef typename divide_typeof_helper<Unit, Unit>::type unit_type; typedef quantity <unit_type, value_type> type; }; } } but that would not work in more complex examples, e.g.: #include <boost/units/systems/si/codata/physico-chemical_constants.hpp> (...) using namespace boost::units::si::constants::codata; typedef boost::mpl::divides<boost::units::energy_dimension, boost::units::amount_dimension>::type Ea_dimension; typedef boost::units::unit<Ea_dimension, boost::units::si::system> Ea; quantity<Ea> ea(0); auto x = ea / (R * aT); Any help would be most appreciated, João Leal

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Boost statechart, how can i transit to previous state using deep_history or shallow history
by juls 16 Apr '16

16 Apr '16

I have a difficulty in understanding the boost statechart history functionality. I have the following state machine. struct InButtonPressed : sc::event<InButtonPressed> {}; struct OutButtonPressed : sc::event<OutButtonPressed> {}; struct InButtonPressed : sc::event<InButtonPressed> {}; struct InputProceed: sc::event<InputProceed> {}; struct OutputProceed: sc::event<OutputProceed> {}; struct CancelEvent: sc::event<CancelEvent> {}; struct Proceed: sc::event<Proceed> {}; struct Revert: sc::event<InputProceed> {}; struct RH_StateMachine : bsc::state_machine< RH_StateMachine, Idle > {}; struct Idle : bsc::state< Idle, RH_StateMachine> { Idle(my_context ctx) : my_base(ctx){ std::cout << "[+] Idle" << std::endl; } ~Idle(){std::cout << "[-] leaving Idle state... \n";} typedef boost::mpl::list< bsc::transition< InButtonPressed, Input>, bsc::transition< OutButtonPressed, Output> >reactions; }; struct Input : bsc::state< Input, RH_StateMachine> { Input(my_context ctx) : my_base(ctx){ std::cout << "[+] Input" << std::endl; } ~Input(){std::cout << "[-] leaving Input state... \n";} typedef boost::bsc::transition< CancelEvent, Cancel> >reactions; }; struct Output : bsc::state< Output, RH_StateMachine> { Output(my_context ctx) : my_base(ctx){ std::cout << "[+] Output" << std::endl; } ~Output(){std::cout << "[-] leaving Output state... \n";} typedef boost::bsc::transition< CancelEvent, Cancel> >reactions; }; struct Cancel::bsc::state<Cancel, RH_StateMAchine>{ Cancel(my_context ctx) : my_base(ctx){ std::cout << "[+] Cancel" << std::endl; } ~Cancel(){std::cout << "[-] leaving Cancel state... \n";} typedef boost::mpl::list< bsc::transition< Proceed, CanceledConfirmed>, bsc::transition< Revert, *"PREVIOUS_STATE"*> >reactions; }; How do i implement transitioning to previous state using deep_history or shallow history, when i can transit to a state from many different states? In the above state machine i want to transit from Cancel state to the previous state when the revert event is triggered, but i have already transited in Cancel state from either Input or Output state... Thank you in advance. -- View this message in context: http://boost.2283326.n4.nabble.com/Boost-statechart-how-can-i-transit-to-pr… Sent from the Boost - Users mailing list archive at Nabble.com.

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option to let program_options remove the flags it recognises
by Brice Rebsamen 14 Apr '16

14 Apr '16

I believe it would be good to add an option to program_options to tell it to remove the flags it recognizes. That would allow to make it work with some other parsers such as gflags etc.

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[property_tree] Json parser with invalid JSON string
by Sébastien Gallou 13 Apr '16

13 Apr '16

Hi all, I experience a strange behavior of parsing non-JSON data with JSON parser. I can create a property_tree from a simple non-JSON string, without exception. And serializing back the result throws : boost::property_tree::ptree m_tree; // Non-JSON to ptree using JSON parser std::istringstream is("1"); // Simple value, non-JSON boost::property_tree::json_parser::read_json(is, m_tree); // ==> No exception, I now have a valid ptree object. // ptree back to JSON std::ostringstream buf; boost::property_tree::json_parser::write_json(buf, m_tree, false); // ==> Exception How can I filter input values that will not be serializable later (= verify that input value is well JSON formatted) ? Thanks for your help, S. Gallou

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boost with c++11
by Christian Meesters 13 Apr '16

13 Apr '16

Dear All, Perhaps my question has been covered already, in this case a pointer to the relevant docs / thread would be highly appreciated. However, I have not been able to find the answer on my question: My code makes use of the C++11 standard and the standard libraries. I feel tempted to employ more current features, also beyond C++11, eventually. When downloading the boost 1.60.0 release and compiling with cxxflags='-std=c++11 -march=native' toolset=gcc linkflags=-stdlib=libc++ supplied to b2 compilation of my software (with gcc 5.3.0) leads to a number of warning messages and deprecation messages related to unused variables or redifined symbols, e.g.: - boost_1_60_0/include/boost/system/error_code.hpp:223:36: warning: ‘boost::system::native_ecat’ defined but not used [-Wunused-variable] static const error_category & native_ecat = system_category(); - /boost_1_60_0/include/boost/iostreams/chain.hpp:256:14: warning: ‘template<class> class std::auto_ptr’ is deprecated [-Wdeprecated-declarations] std::auto_ptr<streambuf_t> In file included from /cluster/gcc/5.3.0/include/c++/5.3.0/memory:81:0, from trunk/src/ngs_io.cpp:8: /cluster/gcc/5.3.0/include/c++/5.3.0/bits/unique_ptr.h:49:28: note: declared here template<typename> class auto_ptr; - /usr/include/boost/iostreams/detail/adapter/concept_adapter.hpp:35:7: note: ‘boost::iostreams::detail::concept_adapter<boost::iostreams::basic_gzip_decompressor<> >::concept_adapter(const boost::iostreams::detail::concept_adapter<boost::iostreams::basic_gzip_decompressor<> >&)’ is implicitly deleted because the default definition would be ill-formed: class concept_adapter { ^ etc. And most importantly this error: /usr/include/boost/iostreams/detail/adapter/concept_adapter.hpp:35:7: error: use of deleted function ‘boost::iostreams::basic_gzip_decompressor<>::basic_gzip_decompressor(const boost::iostreams::basic_gzip_decompressor<>&)’ My g++ compiler flags (other than output and source file) are: -c -fopenmp -O3 -march=native -Wall -ansi -pedantic -Wuninitialized -std=c++11 The code compiles fine with a git pull from May last year, yet I do not recall what I have done differently. So, can anybody tell me how to set up boost, such that compilation and linking against C++11 std-libraries works? I understand that Best regards, Christian Meesters

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Boost Log: I can't see syslog messages sent via boost syslog.
by Anatoly G 11 Apr '16

11 Apr '16

Dear members, I have a question about Boost syslog. I"m beginner Boost user. I created attached code and can't understand why it doesn't work. I execute my code on linux Kubuntu 3.13.0 After execution I"m looking for test strings in syslog file: grep "Test" /var/log/syslog But I don't see any line. I tried to execute commands from shell logger "Test from shell" logger -n 127.0.0.1 -t myapp -p user.notice "Test from shell" I see these lines after executing grep on /var/log/syslog I tried to initialize syslog_backend with boost::log::keywords::use_impl = boost::log::sinks::syslog::native instead of boost::log::keywords::use_impl = boost::log::sinks::syslog::udp_socket_based but then I get compile message, native not defined. I found BOOST_LOG_USE_NATIVE_SYSLOG macro which should be defined during Boost build, but I don't understand how to activate this macro in boost build. Can you please suggest what is the problem? Regards, Anatoly.

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[accumulators] nan error of mean
by Ireneusz Szcześniak 08 Apr '16

08 Apr '16

Hi, I'm using Boost.Accumulators to calculate the standard error of a sample mean, and I'm getting a nan (not a number) as a result, while I should be getting a zero or some number close to it. I boiled down the problem to a small sample that I'm attaching. I would appreciate it if someone could help me out here. Thanks, Irek

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[Boost.Container] flat_set constructor with ordered_unique_range
by dariomt＠gmail.com 08 Apr '16

08 Apr '16

Hi list, If I use the flat_set constructor passing ordered_unique_range, does the library assert in debug mode that the passed data range is indeed ordered and unique? I don't seem to find such assert, but I think it would be very useful, to catch programmer errors. Regards

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seekable input filter definition
by Cherotek Music 07 Apr '16

07 Apr '16

Hey, I'm new to boost and need a seekable input filter that will operate on bytes read from an ifstream. This is what I currently have: struct my_filter : boost::iostreams::seekable_filter{ template<typename Source> int get(Source& src) { int byte = boost::iostreams::get(src); if(byte != EOF && byte != boost::iostreams::WOULD_BLOCK) { // Do something with byte } return byte; } template<typename Sink> bool put(Sink&, char) { // No need to actually implement put because this filter is only used with ifstream return true; } template<typename T> std::streampos seek(T& t, boost::iostreams::stream_offset off, std::ios_base::seekdir way, std::ios_base::openmode which = std::ios_base::in | std::ios_base::out) { return boost::iostreams::seek(t, off, way, which); }}; It works but I would like to get rid of the useless put method. The boost documentation here http://www.boost.org/doc/libs/1_60_0/libs/iostreams/doc/concepts/filter.html says there is an InputSeekableFilter refinement of Filter but I can't seem to understand how to use it (there are no input_seekable_filter_tag or input_seekable_filter structs that I could use). Thanks

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