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Default weight map doesn't work for weighted grid graph in A-star search
by W.P. McNeill 16 Jul '10

16 Jul '10

I am trying to write a simple example of an a-star search over a 2-dimensional grid using the Boost Graph Library. The source is hosted here: http://github.com/wpm/Boost-Searchable-Grid-Example. My intent is for this to be a resource for other people writing a-star searches. I am seeing an error about a missing weight map when I try to compile the call to astar_search(). As far as I can tell, everything is in order. I hoping someone has insight into what I'm missing. My graph class is a rank-2 grid graph called weighted_grid defined like so: typedef grid_graph<2> weighted_grid; I have a simple map that returns a weight of zero for every edge. struct edge_weight_map { typedef float value_type; typedef float reference; typedef edge_descriptor key_type; typedef readable_property_map_tag category; reference operator[](key_type e) const { // All edges have a weight of zero. return 0; } }; I associate this map with the weighted_grid class by specializing property_map. template<> struct property_map<weighted_grid, edge_weight_t> { typedef edge_weight_map type; typedef edge_weight_map const_type; }; I've defined valid expression functions for this property map along with a Euclidean distance heuristic and a visitor that throws an exception when a goal vertex is reached. The complete source is viewable at the URL given above. With these definitions I can do concept checks on the ReadablePropertyMap, ReadablePropertyGraph, VertexListGraph, and AStarHeuristic concepts. I can instantiate a weighted_grid. I can get the edge weight map using get(edge_weight, g) and the vertex index map using get(vertex_index, g). I think I have written everything I need to do a-star search. However, the following call does not build: vertex_descriptor source = vertex(0, g), goal = vertex(3, g); astar_search(g, source, euclidean_heuristic(goal), visitor(astar_goal_visitor(goal)) ); I get a long error spew. The first relevant problem appears to be here: ... /opt/local/include/boost/graph/astar_search.hpp:350: instantiated from ‘void boost::detail::astar_dispatch1(VertexListGraph&, typename boost::graph_traits<G>::vertex_descriptor, AStarHeuristic, CostMap, DistanceMap, WeightMap, IndexMap, ColorMap, const Params&) [with VertexListGraph = boost::grid_graph<2ul, size_t, size_t>, AStarHeuristic = boost::euclidean_heuristic, CostMap = boost::detail::error_property_not_found, DistanceMap = boost::detail::error_property_not_found, WeightMap = boost::edge_weight_map, IndexMap = boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t>, ColorMap = boost::detail::error_property_not_found, Params = boost::bgl_named_params<boost::astar_goal_visitor, boost::graph_visitor_t, boost::no_property>]’ /opt/local/include/boost/graph/astar_search.hpp:372: instantiated from ‘void boost::astar_search(VertexListGraph&, typename boost::graph_traits<G>::vertex_descriptor, AStarHeuristic, const boost::bgl_named_params<P, T, R>&) [with VertexListGraph = boost::weighted_grid, AStarHeuristic = boost::euclidean_heuristic, P = boost::astar_goal_visitor, T = boost::graph_visitor_t, R = boost::no_property]’ main.cpp:36: instantiated from here ... (Line 36 main.cpp is the last line of the astar_search call.) This error message seems to be telling me that the weight map property for edges is missing, but I think I have properly implemented the get(edge_weight, g) function the documentation says is used to create the default weight map. Any idea what I'm doing wrong? Thanks.

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serialization using archive
by Long P 16 Jul '10

16 Jul '10

Hi I have come across the example for serialization in http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/example/serializat… In the following method async_write, the data typename T is put into an archive before being sent out. I would need to do the same thing here but the archive should be binary stream because I need to send this data to a third party application which expects a binary stream. Does anyone know how to do it? Thanks & Regards Long /// Asynchronously write a data structure to the socket. template <typename T, typename Handler> void async_write(const T& t, Handler handler) { // Serialize the data first so we know how large it is. std::ostringstream archive_stream; boost::archive::text_oarchive archive(archive_stream); archive << t; outbound_data_ = archive_stream.str(); // Format the header. std::ostringstream header_stream; header_stream << std::setw(header_length) << std::hex << outbound_data_.size(); if (!header_stream || header_stream.str().size() != header_length) { // Something went wrong, inform the caller. boost::system::error_code error(boost::asio::error::invalid_argument); socket_.io_service().post(boost::bind(handler, error)); return; } outbound_header_ = header_stream.str(); // Write the serialized data to the socket. We use "gather-write" to send // both the header and the data in a single write operation. std::vector<boost::asio::const_buffer> buffers; buffers.push_back(boost::asio::buffer(outbound_header_)); buffers.push_back(boost::asio::buffer(outbound_data_)); boost::asio::async_write(socket_, buffers, handler); } _________________________________________________________________

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postpone thread execution
by Lloyd 15 Jul '10

15 Jul '10

Hi, In boost::thread, when a thread is created, it starts execution at that instance itself. Instead of this, is it possible to postpone the execution? Thanks, Lloyd ______________________________________ Scanned and protected by Email scanner

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boost::lexical_cast<> with hex strings?
by anony 15 Jul '10

15 Jul '10

I'd like to do something like: boost::uint16_t b(std::lexical_cast<boost::uint16_t>("xa")); I have no control of the string stream that lexical_cast uses internally, so how could I implement this? P.S.: There are a lot of false statements made about this functionality on the web, some people claim that boost::lexical_cast<> can do the conversion out of the box, but this is not so in my tests.

4 4

date-time separator
by Conoscenza Silente 15 Jul '10

15 Jul '10

H all I am using posix time to print the current timestamp into a string. boost::posix_time::ptime now( boost::posix_time::microsec_clock::local_time() ); std::string nowString = boost::posix_time::to_iso_extended_string( now ); The output is the following being T the date-time separator 2002-01-31T10:00:01,123456789 Is there any way to change the 'T' char separator with another character or string? I need a space instead of a 'T' Thanks AFG

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Second kind modified Bessel function with complex argument...
by Sedysen 15 Jul '10

15 Jul '10

Hi everybody, I desperatly trying to calculate the Second kind Modified Bessel functions with complex argument... My first question is: can BOOST library perform the task? and if not: does anyone know how can perform the calculation with c/c++ ?

1 0

nested bind() does not compile
by Serguei Kolos 15 Jul '10

15 Jul '10

Hello I'm wondering why the attached code which is using nested boost::bind() does not compile on GCC ( I have tried 4.1 and 4.3). According to the "bind" package documentation nested bind() calls are allowed. To make it compile (and work!) it's necessary to add explicit cast to the result of the nested bind() call, like: boost::function<void ( void )> f = boost::bind( wrapper, a, (boost::function<bool (void)>)boost::bind( cb, p ), b ); But that is something which I don't like. Any ideas? Cheers, Sergei #include <boost/bind.hpp> #include <boost/function.hpp> typedef bool (*Callback)( void * ); void wrapper( int , boost::function<bool (void)> , int ) { } bool callback( void * ) { } void test( Callback c, void * p ) { int a,b; boost::function<void ( void )> f = boost::bind( wrapper, a, boost::bind( c, p ), b ); } int main() { test( callback, 0 ); return 0; }

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Error Installing Boost 1.38
by Amine ABOU MOUGHLBAY 15 Jul '10

15 Jul '10

Hello I am trying to install the Boost 1.38: I am on Ubuntu 10.04 LTS machine I get this error : /home/aaboumou/profiles/default/install/stable/boost_1_38_0/boost/accumulators/statistics_fwd.hpp: In function ?void example1()?: /home/aaboumou/profiles/default/install/stable/boost_1_38_0/boost/accumulators/statistics_fwd.hpp:87: error: ?template<int N> struct boost::accumulators::tag::moment? is not a function, /home/aaboumou/profiles/default/install/stable/boost_1_38_0/boost/accumulators/statistics/moment.hpp:104: error: conflict with ?template<int T2, class Arg1, class A0, class A1, class A2, class A3, class A4, class A5, class A6, class A7, class A8, class A9, class A10, class A11, class A12, class A13, class A14> typename boost::accumulators::detail::extractor_result<Arg1, boost::accumulators::tag::moment<T2> >::type boost::accumulators::extract::moment(const Arg1&, const A0&, const A1&, const A2&, const A3&, const A4&, const A5&, const A6&, const A7&, const A8&, const A9&, const A10&, const A11&, const A12&, const A13&, const A14&)? /home/aaboumou/profiles/default/install/stable/boost_1_38_0/libs/accumulators/example/main.cpp:63: error: in call to ?moment? make[2]: *** [libs/accumulators/example/CMakeFiles/accumulators-accumulators_example.dir/main.cpp.o] Erreur 1 make[1]: *** [libs/accumulators/example/CMakeFiles/accumulators-accumulators_example.dir/all] Erreur 2 make: *** [all] Erreur 2 Any one have ideas to resolve this error ? Thanks a lot for your help. Best Regards ---------------------------------------------------------------------------- Amine ABOU MOUGHLBAY Université Blaise Pascal Doctorant au LASMEA, UMR 6602 du CNRS Membre de l'équipe ROSACE du GRAVIR 24, Avenue des Landais - 63177 AUBIERE Cedex ----------------------------------------------------------------------------

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Storing boost as a 'vendor library' within svn and minimising it's size
by David Aldrich 15 Jul '10

15 Jul '10

Hi We wish to use boost.python in our project that runs on both Windows and Linux platforms. I think that the best way of making boost available to the developers, particularly under Windows, will be as a 'vendor library' within our project's subversion repository. That way, we can control the version of boost in use and make available pre-built binaries. My problem is that I want to minimise the size of that vendor library in order to minimise the time of checkouts and updates within Subversion. This is important as we have developers on the other side of the world, connected via low bandwidth links. First of all, I would welcome any experience or suggestion of how best to share boost, using a vendor library or whatever. Secondly, I have built just the boost.python shared libraries (v.1_43) and then executed 'boost install' to create a directory of just the header files and binaries. This will become the vendor library. Is this a sensible approach? Thirdly, the install directory is 48MB, which is large compared to the other directories in the svn project. I am considering deleting the header file directories not used by boost.python. But this is a trial and error process, as boost.python uses lots of boost header files. Any ideas on how best to do this? I will be very grateful for any advice. With best regards David

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Swap two columns of a matrix
by Alex34 15 Jul '10

15 Jul '10

Hi, I'm using a ublas matrix matrix <double> m_mat(2,2); and I need to swap two columns. Row-major by default I coult not use memcpy. How to do it?

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