August 2013 - Boost-users - lists.preview.boost.org

[BGL] Having a cost function as weight map
by Maxime van Noppen 06 Sep '13

06 Sep '13

Hi, I can't find how to do this pretty basic thing : having a function instead of a field to compute the cost of edges for various path finding algorithms. I couldn't find the answer in the documentation and Google was of no help. Did I miss something obvious ? Example : ------------------- #include <boost/graph/dijkstra_shortest_paths.hpp> #include <boost/graph/graph_traits.hpp> #include <boost/graph/adjacency_list.hpp> struct my_edge { double cost() const { return cost_ * 2; } double cost_; }; struct my_node { }; int main() { typedef boost::adjacency_list< boost::vecS, boost::vecS, boost::directedS, my_node, my_edge > graph_t; typedef boost::graph_traits<graph_t>::vertex_descriptor vertex_t; graph_t graph; vertex_t v /*= ... */; using boost::weight_map; // Works : boost::dijkstra_shortest_paths(graph, v, weight_map(boost::get(&my_edge::cost_, graph))); // Doesn't compile : //boost::dijkstra_shortest_paths(graph, v, // weight_map(boost::get(&my_edge::cost, graph))); } ------------------- Thanks ! -- Maxime

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[chrono] float-based milliseconds?
by Michael Powell 31 Aug '13

31 Aug '13

Hello, Or any of the chrono-steady-clock-based time units... I am noticing some what appear to be rounding errors outputting resulting millisecond values using the boost::chrono::milliseconds(x). It's a design-decision, most if not all of our floating-point values are single-precision-float, don't need to be double-precision-float. When we output the milliseconds(x).count() values, however, what I am finding is that the values are sometimes inaccurate, the same value in 3.0, for instance, output as 2.99995, stuff like this. Is there a way to tell milliseconds what precision floating point it is? float or double? We are targeting ARM, BTW, without hardware floating point support, which is the main reason, I'd like to keep things single-precision float, if at all possible. Thank you... Regards, Michael Powell

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libboost_thread-vc80-mt-1_54.lib
by John Emmas 30 Aug '13

30 Aug '13

A few months ago I downloaded 'boost_1_54_0.zip' which I probably obtained from Sourceforge:- http://sourceforge.net/projects/boost/files/boost/1.54.0/ I'm using libboost with Visual C++ 8 and up to now the only things I've needed from it are 'boost::regex' and 'boost::shared_ptr'. However I'm now building a 3rd party library which seems to want to link to the above library (libboost_thread-vc80-mt-1_54.lib). I'm not sure whether it's a static library or the symbols library for a DLL. Either way, the zip file I downloaded doesn't seem to contain it (nor any other libs or DLLs AFAICT). Q1) Is there some other web site I need to visit in order to get the pre-built binaries? Q2) I know from past experience that pre-built boost binaries sometimes require quite obscure versions of the MSVC runtime. That was the case with boost::regex so after a bit of advice from this mailing list, I ended up making a VC project and building it myself. I don't mind doing the same thing for boost::thread - but I wondered if there was already a suitable project available somewhere? I don't want to re-invent the wheel if a VC project already exists! Thanks. John

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[boost-users][tuple] Tuple::get<0> as std::mem_fun_ref
by Miklós Tóth 30 Aug '13

30 Aug '13

Hi! I have a problem with std::mem_fun_ref and boost::tuple. Here is my code: I have small LevelSetter class. It makes a level vector indexed by a transform_iterator value. template <typename LevelType> class LevelSetter { private: int nmb_of_elements; public: LevelSetter(int nmb_of_elements_) : nmb_of_elements(nmb_of_elements_) {} template <typename TrRange> std::vector<LevelType> set(TrRange range) { typedef typename TrRange::first_type TrIter; std::vector<LevelType> levels(nmb_of_elements); for (TrIter it = range.first; it != range.second; ++it) { levels[*it] = 0.0; } // much more complicated code return levels; } }; Let's call it: class MemFunRefTest { private: typedef float Scalar; typedef boost::tuple<int, Scalar> Tuple; typedef std::vector<Tuple> Fwd; typedef Fwd::iterator FwdIter; typedef std::pair<FwdIter, FwdIter> FwdRange; Fwd elements; public: MemFunRefTest() { elements.push_back(Tuple(0, 400.0)); elements.push_back(Tuple(1, 120.0)); elements.push_back(Tuple(2, 150.0)); } void fun() { FwdRange element_range = std::make_pair(elements.begin(), elements.end()); LevelSetter<Scalar> setter(elements.size()); setter.set(std::make_pair( boost::make_transform_iterator( element_range.first, std::mem_fun_ref(&Tuple::get<0>) ), boost::make_transform_iterator( element_range.second, std::mem_fun_ref(&Tuple::get<0>) ) ) ); } }; When I try to compile i get: error: call of overloaded 'mem_fun_ref(<unresolved overloaded function type>)' is ambiguous candidates are: c:\mingw-4.6\bin\..\lib\gcc\i686-pc-mingw32\4.6.1\..\..\..\..\include\c++\4.6.1\bits\stl_function.h:697: std::mem_fun_ref_t<_Ret, _Tp> std::mem_fun_ref(_Ret (_Tp::*)()) [with _Ret = int&, _Tp = boost::tuples::cons<int, boost::tuples::cons<float, boost::tuples::null_type> >] c:\mingw-4.6\bin\..\lib\gcc\i686-pc-mingw32\4.6.1\..\..\..\..\include\c++\4.6.1\bits\stl_function.h:702: std::const_mem_fun_ref_t<_Ret, _Tp> std::mem_fun_ref(_Ret (_Tp::*)()const) [with _Ret = const int&, _Tp = boost::tuples::cons<int, boost::tuples::cons<float, boost::tuples::null_type> >] What am I missing? Thanks, Miklos

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[typeof] registering class templates whose NTTPs depend on other TPs
by Cromwell Enage 29 Aug '13

29 Aug '13

Hi, all. Using Boost.Typeof, how would I register the following class template? ['' template <typename foo, foo bar> struct baz { }; ''] Any help would be appreciated. Cromwell D. Enage

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CUDA and Boost
by Víctor Felipe 29 Aug '13

29 Aug '13

Hey guys! I have been using Boost inside a Visual C++ CUDA project. I'm using "regex.hpp" inside a ".cu" file and it works fine including it this way: "#include < boost / regex.hpp >". Now, I need to use "abs.hpp", which I'm including this way: "#include < boost / ratio / detail / mpl / abs.hpp >" and it fails while compiling. I'm using Windows 8 64-bits, Visual Studio 2012, Boost 1.53.0 and CUDA 5.5. I get this error only by putting this in my code: "#include < boost / ratio / detail / mpl / abs.hpp >" without using more instructions related with Boost. I have several ".cpp" and ".cu" files in my project. If I put that include in a ".cpp" file, it compiles fine. If I put that include in a ".cu", this error appear: 1>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\boost/ratio/detail/mpl/abs.hpp(68): error C2675: unary '-' : 'T' does not define this operator or a conversion to a type acceptable to the predefined operator Thanks for any help you can provide and sorry for my English, it's not my native language!

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boost asio with scatter gather list and udp ....
by jean-luc malet 29 Aug '13

29 Aug '13

Hi! I'm new to boost, so I don't understand everything, be kind please ;) I'm working on a piece of code that use boost::asio with a ba::ip::udp::socket the code is sending data using 2 buffers stored in a boost::array my work is to write the receiver and my question is : how many udp packets will be sent? 1? 2? if multiple packets are sent, how does boost::asio will re-order them on reception? if one packet is sent, and if on reception I use another scatter gather list as above (but with mutable buffers) how does boost know the size of the 2 buffers? thanks and regards MALET Jean-Luc >

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[posix_time] ARM clock scaling issue
by Michael Powell 28 Aug '13

28 Aug '13

Hello, I am using the posix_time ptime interface to gauge clock times, universal time (Utc), and do date/time math, subtracting for durations type thing. What I am finding is that the accuracy seems to be fast. By how much I don't know, whether that's by a factor of what, or what not, I do not know. We are encountering this on an ARM platform. Has anyone else experience this? If so what can we do to workaround it? Assuming we stick with the Boost API to comprehend date/time, duration, our stopwatch abstraction, elapsed-timer, and so on. Thank you... Regards, Michael Powell

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Meta State Machine, wayward transition
by Archie Campbell 28 Aug '13

28 Aug '13

Hello, I have a simple state machine, that uses only standard rows and no internal transitions, to which I am sending events that are clearly in the transition table for the state that the machine is in, yet the no_transition handler is running for this particular event. I have not yet been able to discover any reasons for a compiling transition table to fail to process an event that is listed in the row against the source state. Have I missed something fundamental? Regards, Archie

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Interprocess : multithreading of the mapping
by Oodini 27 Aug '13

27 Aug '13

Hello, I have several shared memory regions to map in my client process. May I experience troubles if use multithreading to do this operation ? (http://www.boost.org/doc/libs/1_54_0/doc/html/interprocess/sharedmemorybetw…) I have a good reason to do that. Thanks !

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