November 2018 - Boost-users - lists.preview.boost.org

[Spirit] Qi Symbols mapping to AST enum
by Michael Powell 28 Nov '18

28 Nov '18

Hello, I've got a qi::symbols capturing some built-in types. At the moment, I gather, they are mapped to std::string. However, I would rather map them to an AST level enum. For instance, struct builtin_type_t : qi::symbols<char, std::string> { builtin_type_t() { this->add("double", "double") ("float", "float") // ... ; } } builtin_type; Instead, namespace ast { enum type_t { type_double, type_float /* , ... */ }; } struct builtin_type_t : qi::symbols<char, ast::type_t> { builtin_type_t() { this->add("double", ast::type_double) ("float", ast::type_float) // ... ; } } builtin_type; I assume this is possible? Am I missing something about that? Thanks! Michael Powell

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Boost intrusive list volatile hook
by nat ersoz 26 Nov '18

26 Nov '18

I intend to use the boost intrusive list to implement an observer pattern. - The list will cross interrupt boundaries; meaning one interrupt will produce the notifications and the other interrupt will observer the notifications. - The observer, in response to a notification, might detach itself from the list using the the hook's unlink() function. - I think that I will need the hook to be declared volatile in order to accommodate this. I have a minimal code sample here: https://github.com/natersoz/patterns/blob/master/observer/intrusive_list_me… My list hook member declaration: using list_hook_type = boost::intrusive::list_member_hook< boost::intrusive::link_mode<boost::intrusive::auto_unlink> >; list_hook_type hook; My list declaration: using list_type = boost::intrusive::list< Observer<NotificationType>, boost::intrusive::constant_time_size<false>, boost::intrusive::member_hook< Observer<NotificationType>, typename Observer<NotificationType>::list_hook_type, &Observer<NotificationType>::hook> >; If I a the volatile keyword to the list hood type, I cannot figure out how to get the list_type declaration to fit into the list template list. Is it possible? Thank you. -- Nat Ersoz 425-417-5182 (cell)

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Re: [Boost-users] Interprocess: limited boost::any in shared memory
by Ferguson, Neil D CTR (US) 26 Nov '18

26 Nov '18

Mr. de Vries, std::variant looks like it should work splendidly. boost::variant might be even better. Thank you. BTW: this is my first user group interaction; I hope I am responding correctly. Neil Ferguson -----Original Message----- From: Maarten de Vries [mailto:maarten@de-vri.es] Sent: Wednesday, November 21, 2018 1:06 PM To: boost-users(a)lists.boost.org Cc: Ferguson, Neil D CTR (US) <neil.d.ferguson.ctr(a)mail.mil> Subject: [Non-DoD Source] Re: [Boost-users] Interprocess: limited boost::any in shared memory All active links contained in this email were disabled. Please verify the identity of the sender, and confirm the authenticity of all links contained within the message prior to copying and pasting the address to a Web browser. ________________________________ On Wed, 21 Nov 2018 at 20:58, Ferguson, Neil D CTR (US) via Boost-users <boost-users(a)lists.boost.org < Caution-mailto:boost-users@lists.boost.org > > wrote: Sirs and madams, I hope to use boost interprocess shared memory to pass complex and dynamic data structures between processes on a host efficiently. The structures will be comprised only of simple primitives (int, float, etc.), interprocess basic_string, interprocess containers (vectors and maps), containers of containers, and (possible deal killer) boost::any. From the interprocess documentation, it _looks_ like the preceding is doable, aside from boost::any. The boost::any objects will themselves contain only primitives, basic_string, or interprocess vectors of unsigned char. So it _looks_ like the data held by the any should be okay. My question: does boost::any use pointers, references, or other constructs that preclude the class from working in shared memory? Thanks for your advice. Neil Ferguson Take a look at /usr/include/boost/any.hpp . You will see that the actual content of the any object is a pointer created with `new` and cleaned up with `delete`. So this will not work properly in shared memory. You could consider using std::variant instead, which does not put storage on the heap (unless contained objects do it themselves, of course). Kind regards, Maarten de Vries

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IOStream: Determine number of bytes written to array sink
by Peter Klotz 23 Nov '18

23 Nov '18

Hello The program below decompresses a std::string using Boost.IOStream. The target is an array sink of fixed size. The users know the decompressed size in advance but for security reasons I need to check the number of bytes written to the sink. If the array is too small, a "write area exhausted" exception is thrown, which is fine. If the array is too big, decompression succeeds. I would like to check the number of bytes written to the sink and throw an exception. How can I determine how many bytes have been written to the sink? Btw: I cannot use the "counter" filter because of the overhead involved in line counting and because the return value of its characters() method is "int". The buffers involved in my application require a 64 bit data type. Private base class basic_zlib_decompressor of class basic_gzip_decompressor has method total_out() which seems to return the value in question but its return type is also only an "int". Regards, Peter. #include <iostream> #include <stdexcept> #include <iomanip> #include <boost/iostreams/filtering_streambuf.hpp> #include <boost/iostreams/device/array.hpp> #include <boost/iostreams/filter/gzip.hpp> void decompress(const std::size_t p_bufferSize) { // decompressed string is "xy" const std::string s("\x1f\x8b\x08\x08\x58\xce\xf6\x5b\x02\x03\x78\x79\x00\xab\xa8\x04\x00\x99\x28\xe6\x8f\x02\x00\x00\x00",25); boost::iostreams::filtering_streambuf<boost::iostreams::output> filteringStreambuf; filteringStreambuf.push(boost::iostreams::gzip_decompressor()); const std::unique_ptr<char[]> buffer=std::make_unique<char[]>(p_bufferSize); filteringStreambuf.push(boost::iostreams::array_sink(buffer.get(),p_bufferSize)); boost::iostreams::write(filteringStreambuf,s.c_str(),s.size()); boost::iostreams::close(filteringStreambuf); } int main() { try { decompress(3); // works, although only 2 bytes are required, should be made to fail //decompress(2); // works, exactly fills the buffer //decompress(1); // throws exception "write area exhausted" as expected return 0; } catch (const std::exception& e) { std::cout << e.what() << std::endl; } return 1; }

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Overcoming AST forward declaration (includes online example)
by Michael Powell 23 Nov '18

23 Nov '18

Hello, Please find the example posted here: http://wandbox.org/permlink/NI2Luvrw1HF7lF1E The couple of concerns I have in question at the moment are: * How to best handle variants throughout the grammar. Can I use std::variant? Do I need to use boost::variant? Are there additional Spirit features that make this doable? * Embedded in that question is what to do with "nil" or "empty statements" which occurs throughout the grammar at times. I wondered if "empty statement" could synthesize "nothing", literally, not contribute to a variant alternative, for instance. Other AST examples seemed to inject a "struct nil {}" pattern, so I figured maybe this was the better approach? * The real kerfuffle for me at the moment is the AST forward declaration. From what I gather in the protocol, this is an absolute must have. It most occur before Group, and is also used by Message. Thoughts? Suggestions? And, please, before you suggest there are "proto compilers" already available: yes, I know, I've been down that road. I am not looking to parse the proto itself, per se, but rather do some code generation for target language artifacts other than the proto itself. Toward which end, I am also investigating a protoc compiler plugin approach. But I figured, I'd pursue this as a viable path to solving the problem as well, notwithstanding the above challenges. Thanks in advance! Cheers, Michael Powell

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Boost::Filesystem - Handling Unicode paths
by Richard Závodný 22 Nov '18

22 Nov '18

Hello, I have another problem. My program now failing when I want iterate directory which contain files with Unicode characters in it's name. Is there something I should know about? Also I want it to work on both Windows and POSIX platforms, even though I don't expect Unicode characters in POSIX enviroment. Thank you.

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[Spirit] parsing double precision issues
by Michael Powell 22 Nov '18

22 Nov '18

Hello, I am continuing to work through my Protobuf parsing with Constant/Floating-Point tests. Double precision is rearing its ugly head and I am curious what's the best way to handle potentially determining a healthy epsilon given the expected parsed value. For the most part, I think it's going to work, but for the precision issues. Catch: REQUIRE( actual == expected ) with expansion: struct my::protobuf::ast::floating_point_t { 'val': 1.16624e+306, 'opt_sign': null } == struct my::protobuf::ast::floating_point_t { 'val': 1.16624e+306, 'opt_sign': null } with messages: Source: syntax = 'proto2';option L = 1.16624e+306; Delta was: 2.35309e+300 There was clearly a delta involved, most like a precision issue encountered during the parse. Without going into a great deal of depth, if possible: namespace my { namespace protobuf { namespace ast { using float_t = double; enum num_sign_t { sign_none /// '-' , sign_minus /// '+' , sign_plus }; // Which includes struct floating_point_t : numeric_t<float_t> { /* ... */ }; } } } // Without sign, dot required. // >>> TODO: TBD: Precision issue? Or an actual double parsing issue? <<< float_lit %= real_parser<ast::float_t, strict_ureal_policies<ast::float_t>>{}; floating_point_lit %= -num_lit_sign >> float_lit; qi::rule<It, ast::num_sign_t()> num_lit_sign; qi::rule<It, ast::float_t()> float_lit; qi::rule<It, ast::floating_point_t()> floating_point_lit; https://developers.google.com/protocol-buffers/docs/reference/proto2-spec#f… https://developers.google.com/protocol-buffers/docs/reference/proto2-spec#c… https://www.boost.org/doc/libs/1_68_0/libs/spirit/doc/html/spirit/qi/refere… Cheers, Michael Powell

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[asio] UDP recv error handling
by Klebsch, Mario 22 Nov '18

22 Nov '18

Hello, When using boos asio async receiving, my received callback usually looks like this: void ReceiveCB(const boost::system::error_code& error, std::size_t bytes_transferred) { If (error) { fprintf(stderr, "recv() failes: %s\n", error.message().c_str()); return; } /* process data received */ s.async_receive( boost::asio::buffer(...), & ReceiveCB); } I stop calling async_receive() as soon as I get an error. This works good for TCP sockets. But with UDP sockets, recvfrom() can return e.g. the error 'connection refused' after I called sendto() to a peer machine, where no socket is (yet) bound to the destination port number. So, at least after the error 'connection refuxed', I'd better continue calling async_receive_from(). Are there any recommendations on how to decide, whether the receive callback function should re-initiate a receive operation after a receive error or not? Mario Klebsch -- Mario Klebsch Actia I+ME GmbH Mario.klebsch(a)ime-actia.de<mailto:Mario.klebsch@ime-actia.de> Dresdenstrasse 17/18 Fon: +49 531 38 701 716 38124 Braunschweig Fax: +49 531 38 701 88 Germany

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Interprocess: limited boost::any in shared memory
by Ferguson, Neil D CTR (US) 21 Nov '18

21 Nov '18

Sirs and madams, I hope to use boost interprocess shared memory to pass complex and dynamic data structures between processes on a host efficiently. The structures will be comprised only of simple primitives (int, float, etc.), interprocess basic_string, interprocess containers (vectors and maps), containers of containers, and (possible deal killer) boost::any. From the interprocess documentation, it _looks_ like the preceding is doable, aside from boost::any. The boost::any objects will themselves contain only primitives, basic_string, or interprocess vectors of unsigned char. So it _looks_ like the data held by the any should be okay. My question: does boost::any use pointers, references, or other constructs that preclude the class from working in shared memory? Thanks for your advice. Neil Ferguson

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boost::units - converting from one derived_dimension to another across systems (imperial to metric)
by Matt Vinson 21 Nov '18

21 Nov '18

Michael Powell: A) I hope to get Boost.Units to convert all these for me. I am replacing my own unit conversion classes with Boost.Units so there are no masking certain details, magic numbers, etc! Fingers Crossed. B) Boost.Units looks promising. Good to hear it has strong support. I'll keep at it. Thanks!// Steven Watanabe: Got it! You've been very patient and awesome. Thank you, yet again.I updated to this because I do need mass for density conversions:typedef boost::units::make_system< boost::units::us::inch_base_unit, boost::units::us::pound_base_unit, boost::units::us::pound_force_base_unit >::type ip_system; Any issues you see with boost::units::us::pound_base_unit for mass && boost::units::us::pound_force_base_unit for force? If I don't hear from you, I'll presume it's okay. My density unit testing* still passed after adding boost::units::us::pound_force_base_unit so I don't think there are issues. *each of these are converted to the other. enum class DENSITY : char { K_FT3 = 0, K_IN3 = 1, LB_FT3 = 2, LB_IN3 = 3, MT_M3 = 4, MT_CM3 = 5, MT_MM3 = 6, KG_M3 = 7, KG_CM3 = 8, KG_MM3 = 9, LAST = 10 }; On Tuesday, November 20, 2018, 9:09:45 PM CST, boost-users-request(a)lists.boost.org <boost-users-request(a)lists.boost.org> wrote: Send Boost-users mailing list submissions to boost-users(a)lists.boost.org To subscribe or unsubscribe via the World Wide Web, visit https://lists.boost.org/mailman/listinfo.cgi/boost-users or, via email, send a message with subject or body 'help' to boost-users-request(a)lists.boost.org You can reach the person managing the list at boost-users-owner(a)lists.boost.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Boost-users digest..." Today's Topics: 1. Re: boost::units - converting from one derived_dimension to another across systems (imperial to metric) (Michael Powell) 2. Re: Program Options documentation is anaemic (Gavin Lambert) 3. Re: boost::units - converting from one derived_dimension to another across systems (imperial to metric) (Steven Watanabe) 4. Re: Enquiry on boost.geometry and intersection() (Adam Wulkiewicz) ---------------------------------------------------------------------- Message: 1 Date: Tue, 20 Nov 2018 20:55:19 -0500 From: Michael Powell <mwpowellhtx(a)gmail.com> To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] boost::units - converting from one derived_dimension to another across systems (imperial to metric) Message-ID: <CAMEoF_GFTg_Fx4haDdb2i65fEaOB_hnG8QmrgshMSG5-0XT5mQ(a)mail.gmail.com> Content-Type: text/plain; charset="UTF-8" On Tue, Nov 20, 2018 at 8:47 PM Matt Vinson via Boost-users <boost-users(a)lists.boost.org> wrote: > > degski: I do not think am making the "nauseam" mistake. My issue is using Boost.Units correctly which I concede is difficult for me but I am reading the docs and trying to get it. > In our field of engineering, we use Kg as a force; not a mass. (We also use pound as a force; not a mass - for your "UK's Weights and Measures Act 1963" counterpart). That said, I should not have made the mistake of using Kg as a force in Boost.Units, it's true. Shame on me. > My task is to convert between lineal forces: k/ft, k/in, lb/ft, lb/in, kN/m, kN/cm, kN/m, N/m, N/cm, N/m, Metric ton/m, Metric ton/cm, Metric ton/mm, Kg/m, Kg/cm, Kg/mm. These are all force/length. Coming from an energy oil and gas background applying Boost.Units, that's a difficult conversation to have especially when "units" are used, but in fact are masking certain details, magic numbers, etc, confounding their dimensions. > Steven Watanabe: Thank you, again. > #1: I was not trying to say it's wrong; sorry. Just that I did not see 'length' and opted for the one that did. The unit's are correct, as you say. > #2: This is an error to start with Kg(force)/meter. I can start with N/meter. I've changed this variable name to newton_per_meter and the conversion factors. I can tell you this much; once you get reasonably proficient with Boost.Units, there is a strong compiler confidence in correctness once you have your dimensions, units, etc, meshing well together. By that I mean, in truth, compile time confidence. The compiler / Boost.Units will tell you when you have it wrong, and it will compile when you have it correct. That's a major plus in my book. Cheers, best of luck! > *.h----------------------------------------------------- > > namespace dimensional_analysis { > > typedef boost::units::length_base_dimension::dimension_type length_dimension; > > typedef boost::units::mass_base_dimension::dimension_type mass_dimension; > > typedef boost::units::make_system<boost::units::us::inch_base_unit,boost::units::us::pound_base_unit>::type ip_system; > > namespace lineal_force { > > typedef boost::mpl::divides<boost::units::force_dimension,boost::units::length_dimension>::type lineal_force_dimension; > > namespace imperial { > > //////////////// > > ////lb/in, right? > > ////boost::units::force_dimension = pound > > ////boost::units::length_dimension = in > > //////////////// > > typedef boost::units::unit<lineal_force_dimension,lengths::ip_system> lineal_force_unit; > > } > > namespace si { > > //////////////// > > ////N/m, right? > > ////boost::units::force_dimension = newton > > ////boost::units::length_dimension = meter > > //////////////// > > typedef boost::units::unit<lineal_force_dimension,boost::units::si::system> lineal_force_unit; > > } > > }//lineal_force > > }//dimensional_analysis > > *.cpp----------------------------------------------------- > > //Imperial lb/in to SI N/m > > BOOST_UNITS_DEFINE_CONVERSION_FACTOR( > > dimensional_analysis::lineal_force::imperial::lineal_force_unit, > > dimensional_analysis::lineal_force::si::lineal_force_unit, > > double, > > 175.1268369864); // exact conversion > > BOOST_UNITS_DEFAULT_CONVERSION( > > dimensional_analysis::lineal_force::imperial::lineal_force_unit, > > dimensional_analysis::lineal_force::si::lineal_force_unit); > > //SI N/m to Imperial lb/in > > BOOST_UNITS_DEFINE_CONVERSION_FACTOR( > > dimensional_analysis::lineal_force::si::lineal_force_unit, > > dimensional_analysis::lineal_force::imperial::lineal_force_unit, > > double, > > 0.1837185501); // exact conversion > > BOOST_UNITS_DEFAULT_CONVERSION( > > dimensional_analysis::lineal_force::si::lineal_force_unit, > > dimensional_analysis::lineal_force::imperial::lineal_force_unit); > > //Imperial to SI. This should convert lb/in to N/m and return 175.1268369864 (N/m) > > //But it does not. Its converting lb (mass) to Kg (mass), 0.454 > > const auto t2 = static_cast<boost::units::quantity<dimensional_analysis::lineal_force::si::lineal_force_unit>>( > > 1.0 * dimensional_analysis::lineal_force::imperial::lineal_force_unit::unit_type()); > > //Again, Imperial to SI. This should convert lb/in to N/m and return 175.1268369864 (N/m) > > //But it does not. It returns lb (mass) to Kg (mass) > > const auto t3 = boost::units::conversion_factor( > > dimensional_analysis::lineal_force::imperial::lineal_force_unit::unit_type(), > > dimensional_analysis::lineal_force::si::lineal_force_unit::unit_type()); > > //SI to Imperial. This should convert N/m to lb/in and return 0.1837185501 (lb/in) > > //But it does not. Its converting Kg (mass) to lb (mass), 2.205 > > const auto t1 = static_cast<boost::units::quantity<dimensional_analysis::lineal_force::imperial::lineal_force_unit>>( > > 1.0 * dimensional_analysis::lineal_force::si::lineal_force_unit::unit_type()); > > //So, I don?t know why the library is converting mass; I?ve tuned it to use boost::units::force_dimension/boost::units::length_dimension > > //I am doing something wrong where the library is not using force/length. > > //Below does work, mainly. > > //This is convert Si to SI and return value of 1.0 is correct. > > const auto t4 = static_cast<boost::units::quantity<dimensional_analysis::lineal_force::si::lineal_force_unit>>( > > 1.0 * boost::units::si::newton / boost::units::si::meter); > > //This convert lb/in to SI and return value is 175.1268369864 is correct. > > const auto t5 = static_cast<boost::units::quantity<dimensional_analysis::lineal_force::si::lineal_force_unit>>( > > 1.0 * boost::units::us::pound_force_base_unit::unit_type() / boost::units::us::inch_base_unit::unit_type()); > > //This converts lb/in to lb/in and return value is of 1.0 is correct. > > const auto t6 = static_cast<boost::units::quantity<dimensional_analysis::lineal_force::imperial::lineal_force_unit>>( > > 1.0 * boost::units::us::pound_force_base_unit::unit_type() / boost::units::us::inch_base_unit::unit_type()); > > //This is 2.205 and not correct. > > //It?s not converting SI-force/length to Imperial-force/length > > //Its converting Kg (mass) to lb (mass), 2.205 > > const auto t7 = static_cast<boost::units::quantity<dimensional_analysis::lineal_force::imperial::lineal_force_unit>>( > > 1.0 * boost::units::si::newton / boost::units::si::meter); > > //What have I done wrong? > > //Any help is appreciated. > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > https://lists.boost.org/mailman/listinfo.cgi/boost-users ------------------------------ Message: 2 Date: Wed, 21 Nov 2018 15:55:35 +1300 From: Gavin Lambert <boost(a)mirality.co.nz> To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] Program Options documentation is anaemic Message-ID: <3ab79a24-e6ff-e311-1d12-adbe5646a123(a)mirality.co.nz> Content-Type: text/plain; charset=utf-8; format=flowed On 20/11/2018 23:03, David Demelier wrote: > Reading the type_value documentation from Boost Program options feels like: > > ??? typed_value * composing(); > ??? Specifies that the value is composing. See the 'is_composing' > method for explanation. > > And the documentation of is_composing: > > ??? bool is_composing() const; > > Not sure if I know more what this function is supposed to do now. I agree that this seems somewhat unhelpful. FWIW a quick look elsewhere found https://www.boost.org/doc/libs/1_68_0/doc/html/program_options/tutorial.htm… which describes that option in more detail -- specifically that it's whether repeated parameters are merged or just replace the older value. > Also, I think this module/documentation should take a s/method/function/g. "Method" is the more common name for a method within a class. ------------------------------ Message: 3 Date: Tue, 20 Nov 2018 19:58:27 -0700 From: Steven Watanabe <watanabesj(a)gmail.com> To: Matt Vinson via Boost-users <boost-users(a)lists.boost.org> Cc: matt.vinson(a)sbcglobal.net Subject: Re: [Boost-users] boost::units - converting from one derived_dimension to another across systems (imperial to metric) Message-ID: <4f601999-f01c-0535-37a3-15e6e21d8331(a)gmail.com> Content-Type: text/plain; charset=utf-8 AMDG On 11/20/2018 06:46 PM, Matt Vinson via Boost-users wrote: > <snip> > <some reformatting to reduce line wrapping> > *.h----------------------------------------------------- > > namespace dimensional_analysis { > > ????typedef length_base_dimension::dimension_type length_dimension; > ????typedef mass_base_dimension::dimension_type mass_dimension; > > typedef make_system<inch_base_unit,pound_base_unit>::type ip_system; > This should be pound_force_base_unit. > ? namespace lineal_force { > ??? typedef mpl::divides<force_dimension,length_dimension>::type lineal_force_dimension;?????????? > > ??? namespace imperial { > > ????? //////////////// > ????? ////lb/in, right? > > ////boost::units::force_dimension =pound > ////boost::units::length_dimension = in > ????? //////////////// > ????? typedef unit<lineal_force_dimension,lengths::ip_system> lineal_force_unit; This unit is nonsensical because the ip_system as written is unable to represent the lineal_force_dimension. That this doesn't give a hard compiler error is a bug in the library. Once you fix ip_system, the conversions should be right. > ??? } > ??? namespace si { > ??? //////////////// > ??? ////N/m, right? > Yep. > ////boost::units::force_dimension = newton > ////boost::units::length_dimension = meter > ????? //////////////// > ????? typedef unit<lineal_force_dimension,si::system> lineal_force_unit; > ??? } > ? }//lineal_force > }//dimensional_analysis > > *.cpp----------------------------------------------------- > > //Imperiallb/in to SI N/m > The following conversion definitions are unnecessary and have no effect: > BOOST_UNITS_DEFINE_CONVERSION_FACTOR( > dimensional_analysis::lineal_force::imperial::lineal_force_unit, > dimensional_analysis::lineal_force::si::lineal_force_unit, > double, > 175.1268369864); // exact conversion > > BOOST_UNITS_DEFAULT_CONVERSION( > dimensional_analysis::lineal_force::imperial::lineal_force_unit, > dimensional_analysis::lineal_force::si::lineal_force_unit); > > //SI N/mto Imperial lb/in > > BOOST_UNITS_DEFINE_CONVERSION_FACTOR( > dimensional_analysis::lineal_force::si::lineal_force_unit, > dimensional_analysis::lineal_force::imperial::lineal_force_unit, > double, > 0.1837185501); // exact conversion > > BOOST_UNITS_DEFAULT_CONVERSION( > dimensional_analysis::lineal_force::si::lineal_force_unit, > dimensional_analysis::lineal_force::imperial::lineal_force_unit); > > <snip> > In Christ, Steven Watanabe ------------------------------ Message: 4 Date: Wed, 21 Nov 2018 04:09:11 +0100 From: Adam Wulkiewicz <adam.wulkiewicz(a)gmail.com> To: Zhang Qun <zhangq.rhy(a)gmail.com> Cc: boost-users(a)lists.boost.org Subject: Re: [Boost-users] Enquiry on boost.geometry and intersection() Message-ID: <9d3e335d-df1a-7627-af4f-a9d3fd8c22ff(a)gmail.com> Content-Type: text/plain; charset="utf-8"; Format="flowed" Please do not top-post. Zhang Qun?wrote: > Hi Adam > I think I have figured it out. Because of the precision, the two > polygons are not the same. > > That also explains that why sometimes the intersection() gives me two > intersection points looking "exactly" the same but if you look at the > double precision, they are actually two different points. In reality, > these two points can be safely considered the same point. I can solve > this by comparing the two points distance. However, sometimes also > because of the precision, the intersection() does not even give me any > intersection points especially when the line is right across the > vertex of the polygon. How do I solve this kind of problem? Could you paste the WKTs of geometries (with sufficient precision) [1] and say what do you get and what do you expect? [1] e.g. std::cout << std::setprecision(20) << bg::wkt(polygon) << std::endl; Adam

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