February 2016 - Boost-users

Re: [Boost-users] [Serialization] This compiles; but does it work?
by Bjorn Reese 19 Feb '16

19 Feb '16

On 02/19/2016 04:20 AM, Merrill Cornish wrote: > Can anyone tell me if this will work, or do I need to implement the > serialize() function? When you are doing different things for the input and output archives then it is better to split serialization into load and save: #include <boost/filesystem/path.hpp> #include <boost/serialization/split_free.hpp> namespace boost { namespace serialization { template <typename Archive> void serialize(Archive& ar, filesystem::path& p, const unsigned int version) { split_free(ar, p, version); } template<class Archive> void save(Archive & ar, const filesystem::path& p, unsigned int version) { ar << p.string(); } template<class Archive> void load(Archive & ar, filesystem::path& p, unsigned int version) { std::string data; ar >> data; p = data; } }}

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[graph] Search algorithm using quality metric rather than distance
by rleigh＠codelibre.net 19 Feb '16

19 Feb '16

I have an adjacency_list graph (shown in attached dot file). Each edge has an attached "quality metric" as a bundled property. Similar to the dijkstra_shortest_paths algorithm, I'd like to determine the optimal path. However, this algorithm sums the distance along each edge, and finds the shortest path. What I'd like to do is *multiply* the quality metric for each edge in the path, and find the largest one. A perfect path will have a quality metric of 1.0, while suboptimal paths will have values tending towards zero, and the more "bad" edges the smaller the number. I'll likely then look at the number of edges and then select the shortest of the candidates. It seems like a simple algorithm that might already be included, but I just haven't found it yet not knowing its formal name. If anyone has any suggestions, I'd be very grateful. Many thanks, Roger

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[Serialization] This compiles; but does it work?
by Merrill Cornish 19 Feb '16

19 Feb '16

mGraphFile is a data member of type boost:filesystem::path, which isn't (as I understand) handled natively by Boost Serialization. I could define template<class Archive> void serialize(Archive& ar, boost::filesystem::path& p, const unsigned int version); but it is needed in only one place. Below is an excerpt from an inline serialization function that I'm already using. While it has a redundant step not needed for loading and a different redundant step not needed for storing, it would seem to do what I need. (The minor inefficiency of the redundant statements is of no concern here.) ... std::string str = mGraphFile.string(); // redundant if loading ar & BOOST_SERIALIZATION_NVP(str); mGraphFile = str; // redundant if saving ... Can anyone tell me if this will work, or do I need to implement the serialize() function? Merrill Cornish

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boost::msm usage: how to set properties of target states
by spiritwalker 18 Feb '16

18 Feb '16

States in my fsm has different properties. I define a event which will invoke a transition to a target state. I want to set properties of target by event data. My choices are: 1. set properties in the action or guard: but it is still in the source state. I fill not good if i set the target state properties at the time 2. set properties in the target entry: but the value of properties have been calculated in guard on receiving the event so i should recalculated again :( Any one can give me more ideas. Thanks ! -- View this message in context: http://boost.2283326.n4.nabble.com/boost-msm-usage-how-to-set-properties-of… Sent from the Boost - Users mailing list archive at Nabble.com.

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SERIALIZE: Registering derived templete classes serialized via base ptr
by Unger, Jörg 17 Feb '16

17 Feb '16

I'm trying to serialize a derived class via a base ptr using boost serialize. The example to illustrate the problem (without templates) is as follows //****************** Main.cpp ********************** #include <fstream> #include <boost/archive/text_iarchive.hpp> #include <boost/archive/text_oarchive.hpp> #include "Derived.h" int main(int argc, char* argv[]) { std::string fileName = "Out.txt"; Derived myDerived; Base* myBasePtr = &myDerived; //myDerived.foo(); // serialize it as txt std::ofstream ofs(fileName.c_str(), std::ios_base::binary ); boost::archive::text_oarchive ota ( ofs, std::ios::binary ); //ota & boost::serialization::make_nvp(std::string("directly derived").c_str(), myDerived);; ota & boost::serialization::make_nvp(std::string("via base ptr").c_str(), myBasePtr);; return 0; } //*********************************************** //*************** Base.h ************************* #pragma once #include <boost/serialization/access.hpp> #include <boost/serialization/export.hpp> class Base { friend class boost::serialization::access; public: Base(){}; virtual ~Base(){}; template<class Archive> void serialize(Archive & ar, const unsigned int version) {}; }; BOOST_CLASS_EXPORT_KEY(Base) //*********************************************** //**************** Derived.h ********************** #pragma once #include <boost/serialization/access.hpp> #include <boost/serialization/export.hpp> #include "Base.h" class Derived : public Base { friend class boost::serialization::access; public: Derived(){}; void foo(); template<class Archive> void serialize(Archive & ar, const unsigned int version); }; BOOST_CLASS_EXPORT_KEY(Derived) //*********************************************** //**************** Derived.cpp ******************** #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> #include "Derived.h" //Derived::Derived() //{} void Derived::foo() { } // serializes the class template void Derived::serialize(boost::archive::text_oarchive & ar, const unsigned int version); template void Derived::serialize(boost::archive::text_iarchive & ar, const unsigned int version); template<class Archive> void Derived::serialize(Archive & ar, const unsigned int version) { ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(Base); } BOOST_CLASS_EXPORT_IMPLEMENT(Derived) //*********************************************** When compiling the above code and linking the object files, everything works fine. When I combine everything in a library (in this example it is essentially only Derived.o) and link the main file with the library, I get an error what(): unregistered class - derived class not registered or exported The problem seems to be that the registration in the linked library is not activated. The problem is simplified here, because in our implementation, the derived class is essentially a template class that does not have any cpp-files. We have just added another otherwise empty cpp file with the registration of all possible instantiations of the class. There are several possibilities to solve the problem · The macro BOOST_CLASS_EXPORT_IMPLEMENT(Derived) could be moved to the main.cpp. This workaround is not my preferred options, since the registration has to be done in every main file we want to use the library for. · The macro BOOST_CLASS_EXPORT_IMPLEMENT(Derived) could be moved to the Base.cpp (the constructor for the base class has to be implemented in this file as well). This is another option, but this requires the header files of the derived classes to be included in Base.cpp, which is not convenient either. · Serialize one object of the derived class before serialization through the pointer, but that's only a workaround. (see the commented line in Main.cpp) · Call the foo method in Main.cpp. Surprisingly, this does not depend on whether the foo function is implemented in Derived.cpp, but also if it is called in Main.cpp. Surprisingly, if "myDerived.foo();" in Main.cpp is uncommented the program works fine, which is something I do not understand. It seems that the registration is only performed, if one of the functions in this cpp file is actually called, or am I wrong? · Implement the constructor of Derived in Derived.cpp. This approach works fine for the current example (somehow similar to the previous solution). However, in our case, Derived is a template and thus the constructor can't be implemented in the cpp file. · Another option is to always link the main file with the library and the object file Derived.o, but this is also not a convenient option. · Finally, a manual registration with register_type is possible. This could be moved to a separate subroutine that is always called in different main files. What is the recommended way of registering derived template classes that are serialized through a base ptr within a library. Best regards, Jörg F. Unger

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[Timer] unresolved external symbol boost::chrono::time_point
by Aman Wardak 17 Feb '16

17 Feb '16

Env: Win7 32-bit running in VirtualBox on Macbook Pro Compiler: MS Visual Studio 14 It's my first time working with Boost. I've followed the instructions here: http://www.boost.org/doc/libs/1_60_0/more/getting_started/windows.html I've compiled Boost successfully: ============================ The Boost C++ Libraries were successfully built! The following directory should be added to compiler include paths: C:\Users\IEUser\Documents\boost_1_60_0 The following directory should be added to linker library paths: C:\Users\IEUser\Documents\boost_1_60_0\stage\lib ============================================== I've added the above paths in Visual Studio and was able to run the test in step 6 of the instructions linked above to verify my environment is set up correctly. MY PROBLEM: I'm trying to compile the very first sample code at this link: http://www.boost.org/doc/libs/1_60_0/libs/timer/doc/cpu_timers.html I get the following error: ------ Build started: Project: BoostExample, Configuration: Debug Win32 ------ Source.cpp libboost_timer-vc140-mt-gd-1_60.lib(cpu_timer.obj) : error LNK2019: unresolved external symbol "public: static class boost::chrono::time_point<class boost::chrono::steady_clock,class boost::chrono::duration<__int64,class boost::ratio<1,1000000000> > > __cdecl boost::chrono::steady_clock::now(void)" (?now@steady_clock @chrono@boost@@SA?AV?$time_point@Vsteady_clock@chrono@boost@@V?$duration@ _JV?$ratio@$00$0DLJKMKAA@@boost@@@23@@23@XZ) referenced in function __catch$??1auto_cpu_timer@timer@boost@@QAE@XZ$0 C:\Users\IEUser\Documents\Visual Studio 2015\Projects\CS2370\Debug\BoostExample.exe : fatal error LNK1120: 1 unresolved externals ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Thanks, Aman

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[Test] BOOST_CHECK_EXCEPTION error message still vague
by Merrill Cornish 17 Feb '16

17 Feb '16

In BOOST_1_59_0, I complained that the error message from BOOST_CHECK_EXCEPTION was indecipherable. In BOOST_1_60_0, things improved a lot. But it still leave you hanging. I use the function fail_msg() as the predicate argument to BOOST_CHECK_EXCEPTION. If it finds a specified substring in the exception message, it returns true. Otherwise, it returns false. Below is an error message from BOOST_CHECK_EXCEPTION when the predicate returned false: exception "std::runtime_error" raised as expected: validation on the raised exception through predicate "fail_msg" The first clause says my code raised the expected exception class. That part of the message is clear and unambiguous. The second clause, however, is a non-sequitur. It seems to only acknowledge that there was a predicate named "fail_msg" without saying whether it returned true or false. Overall, the whole message doesn't say whether BOOST_CHECK_EXCEPTION passed or failed. Since a message was output, the user can assume things did not go well, but it seems like the message could be more explicit. Merrill Cornish

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multiprecision max and et_on
by Daniel Brake 16 Feb '16

16 Feb '16

Hi Boost, I would like to be able to use the Eigen linear algebra library with Boost.Multiprecision with et_on. However, as noted here: https://svn.boost.org/trac/boost/ticket/11149 for max, et_on isn't compatible out of the box. Aside from writing my own little overload for max for the particular form being produced in my line of code from within Eigen, does anyone have a fix for enabling max with expression templates on? MWE: { using mpfr = boost::multiprecision::mpfr_float; // et_on by default, which is what i want using std::max; mpfr a(1), b(2), c(4); auto q = b*b+c; mpfr r = max(a,q); } Thanks a lot, Daniel

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[GIL] Why doesn't pixel assignment color-convert?
by Stonewall Ballard 16 Feb '16

16 Feb '16

I've just started using boost.gil, though I've been looking at it for a while. It seems odd to me that assignment doesn't do an implicit color_convert() when the pixels are of different types. Instead, it just copies matching channels. That's the wrong thing to do when assigning an rgba pixel to an rgb pixel, since the former is straight and the latter is premultiplied. It also seems wrong that you can assign an rgba pixel to an rgb pixel, but not vice-versa. It looks like this is caused by pixels_are_compatible in gil_concept.hpp, where it fails to check that both pixels have the same number of channels. Instead, it matches channels of the output pixel against the input pixel, ignoring any extra input pixel channels. It also ignores scoped_channel_value usage. This seems like an error waiting to happen. Comments? - Stoney

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ASIO: add work and remove immed., will ignore further handler_requests???
by aj neu 16 Feb '16

16 Feb '16

Hi, below is some code where boost::asio::io_service::work is added, and then immediately removed. After that, I call async_wait on a steady_timer, but it does not work: io.run() RETURNS IMMEDIATELY, and IGNORES the async_wait. Is this intended? (I was rather surprised, because I thought that the async_wait would schedule new work, but it does not work). If I cange the code-line #define WEIRD_BEHAVIOUR to #undef WEIRD_BEHAVIOUR then I have my expected behaviour. Thanks, ajneu #include <iostream> #include <chrono> #include <experimental/optional> #include <boost/asio.hpp> #include <boost/asio/steady_timer.hpp> #define WEIRD_BEHAVIOUR int main() { boost::asio::io_service io; std::experimental::optional<boost::asio::io_service::work> work; #ifdef WEIRD_BEHAVIOUR work.emplace(io); work = std::experimental::nullopt; #endif boost::asio::steady_timer timer(io, std::chrono::milliseconds{1000}); timer.async_wait([](const boost::system::error_code &ec) { std::cout << ((!ec) ? "done" : "err") << std::endl; }); io.run(); }

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