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[iostreams] mapped_file path issue
by Alexandre 24 Mar '13

24 Mar '13

Hello, After reading through all the documentation and examples I could read, I still can't get the following piece of code to work . I assume that when you pass a new_file_size and a path to the mapped_file_params class , it will then open the file at the location desired when I call the constructor of mapped_file with the mapped_file_params object in parameter. But the only thing it does is to create a file with a weird name , like "%F8/134" in the project working directory, not where I told it to. Maybe I'm wrong and one should create file before specifying it to the mapped_file? After reading the doc, I was under the assumption that it created a new file when you fill in the new_file_size param. and specifies the filename. Anyone experienced this before? Any advice on how to resolve this? Here's the code: boost::iostreams::mapped_file_params param(filename); // filename is a std::string with the correct path param.flags = boost::iostreams::mapped_file::mapmode::readwrite; param.new_file_size = sizeNeeded; // sizeNeeded is the size of the data param.length = sizeNeeded; boost::iostreams::mapped_file fileMap(param); // at this point the file is created … Thanks for your time, Alexandre

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[BGL] boost::disjoint_set getting new representative after link()
by Adi Shavit 23 Mar '13

23 Mar '13

Hi, I'm using boost::disjoint_sets_with_storage<>. After calling link(rep1, rep2), I want to know the new rep - the representative of the merged set. Obviously, I can call find_set(rep1) to find it. I assume that the extra call to find_set incurs an additional run-time cost per call to link. Is this true or is the call immediate (as in returning the immediate parent of rep1)? If it does incur a run-time cost, then we know that the new-rep is *either *rep1 or rep2. Is there some other way to know which one it is? On a related matter, I am also tracking the *size *of the sets for each link(). Does knowing the size of the rep set before the link help in determining which of rep1 or rep2 will be the new rep? Is there a simple way to extend boost::disjoint_sets_with_storage<> to do the size tracking internally (currenlty I keep an external size vector per rep to keep track of the link()s). Thanks, Adi

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erase and put methods in property tree lib of boost
by Sashidhar Guntury 23 Mar '13

23 Mar '13

I have been trying to use the put and erase methods in boost's property tree library with very limited success. I have tried to go through the documentation but it seems really esoteric with no real example to demonstrate. This is what I would like to do - I have a json object. I look for a particular key (call it "title") and extract the corresponding value (call it "Eric Clapton"), do something with "Eric Clapton" (say change it to "ec") insert it in the place of the old value. Now, should I do an "erase" to remove the previous entry and then "put" the new pair? Will "put" replace the old value? void doSomething(const ptree& node) { ... BOOST_FOREACH(const ptree::value_type& child, node.get_child("artists")) { string text = child.second.get<string>("title"); // do something to the text to give text2 child.second.put("title", text2); } ... } The above code gives an error which is equally hard to understand. I was hoping someone would shed some light. thanks Sashidhar

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[BGL] Error C2679 when inserting edge property to subgraph
by Nicholas Mario Wardhana 22 Mar '13

22 Mar '13

Hi all, Could somebody tell me how to add a bundled edge property for subgraph, please? The code, based on [1], is as follows. // code starts #include <boost/config.hpp> #include <boost/graph/subgraph.hpp> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/graph_utility.hpp> using namespace std; using namespace boost; struct VertexProperty { int intValue; }; struct EdgeProperty { std::size_t biconnected_component; int intValue; }; typedef adjacency_list<vecS, vecS, undirectedS, VertexProperty, property<edge_index_t, int, EdgeProperty> > PlainGraph; typedef subgraph<PlainGraph> Graph; int main(int argc, char* argv[]) { PlainGraph g1; Graph g(2); VertexProperty v0; v0.intValue = 1; VertexProperty v1; v0.intValue = 1; EdgeProperty e; e.biconnected_component = 0; e.intValue = 0; add_edge(0, 1, g); put(get(vertex_bundle,g), 0, v0); // OK put(get(vertex_bundle,g), 1, v1); // OK put(get(edge_bundle,g), 0, e); // error here return 0; } // code ends The error is as follows: // error starts 1>D:\API\boost_1_53_0\boost/property_map/property_map.hpp(361): error C2679: binary '[' : no operator found which takes a right-hand operand of type 'int' (or there is no acceptable conversion) 1> D:\API\boost_1_53_0\boost/graph/subgraph.hpp(797): could be 'EdgeProperty &boost::subgraph_global_property_map<GraphPtr,PropertyMap,Tag>::operator [](boost::detail::edge_desc_impl<Directed,Vertex>) const' 1> with 1> [ 1> GraphPtr=boost::subgraph<PlainGraph> , 1> PropertyMap=boost::adj_list_edge_property_map<boost::undirected_tag,EdgeProperty,EdgeProperty &,unsigned __int64,boost::property<boost::edge_index_t,int,EdgeProperty>,boost::edge_bundle_t>, 1> Tag=boost::edge_bundle_t, 1> Directed=boost::undirected_tag, 1> Vertex=unsigned __int64 1> ] 1> while trying to match the argument list '(const boost::subgraph_global_property_map<GraphPtr,PropertyMap,Tag>, int)' 1> with 1> [ 1> GraphPtr=boost::subgraph<PlainGraph> , 1> PropertyMap=boost::adj_list_edge_property_map<boost::undirected_tag,EdgeProperty,EdgeProperty &,unsigned __int64,boost::property<boost::edge_index_t,int,EdgeProperty>,boost::edge_bundle_t>, 1> Tag=boost::edge_bundle_t 1> ] 1> main.cpp(74) : see reference to function template instantiation 'void boost::put<boost::subgraph_global_property_map<GraphPtr,PropertyMap,Tag>,EdgeProperty&,int,EdgeProperty>(const boost::put_get_helper<Reference,LvaluePropertyMap> &,K,const V &)' being compiled 1> with 1> [ 1> GraphPtr=boost::subgraph<PlainGraph> , 1> PropertyMap=boost::adj_list_edge_property_map<boost::undirected_tag,EdgeProperty,EdgeProperty &,unsigned __int64,boost::property<boost::edge_index_t,int,EdgeProperty>,boost::edge_bundle_t>, 1> Tag=boost::edge_bundle_t, 1> Reference=EdgeProperty &, 1> LvaluePropertyMap=boost::subgraph_global_property_map<boost::subgraph<PlainGraph> ,boost::adj_list_edge_property_map<boost::undirected_tag,EdgeProperty,EdgeProperty &,unsigned __int64,boost::property<boost::edge_index_t,int,EdgeProperty>,boost::edge_bundle_t>,boost::edge_bundle_t>, 1> K=int, 1> V=EdgeProperty 1> ] 1> // error ends I found a few other threads [2, 3] about this, but their solutions don't solve the problem. BTW I use Visual Studio 2010 on Windows 7 64-bit. The Boost version is 1.53.0. Thank you! Best regards, Nicholas Mario Wardhana References: [1] http://boost.2283326.n4.nabble.com/BGL-Bundled-Properties-in-subgraphs-td25… [2] http://stackoverflow.com/questions/7608031/boost-subgraph-and-bundled-prope… [3] https://groups.google.com/forum/?fromgroups=#!topic/boost-list/5EIkKybaUTY

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[boost][units]: Looking for more elegant ways to define RPM and velocity[km/h]
by Dennis Gertitschke 22 Mar '13

22 Mar '13

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Martin Lester : 3/22/2013 4:03:04 AM
by Martin Lester 22 Mar '13

22 Mar '13

http://www.sanjose-personalinjuryattorney.com/btjh/bdmm.aabn Martin Lester 3/22/2013 4:03:04 AM

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[Thread] Constructing a move-only object asyncronously
by Alexander Lamaison 20 Mar '13

20 Mar '13

I'm trying to create a move-only object asyncronously using Boost.Thread unique_future but I'm running into trouble: error C2248: 'A::A' : cannot access private member declared in class 'A' c:\users\awl03\documents\visual studio 2005\projects\boost_1_51_0\boost\thread\future.hpp 493 I've tried all sorts of ways to work around this but always end up with some variation or other of this error message. What am I doing wrong? The code is below. The setup is: Visual Studio 2005 Boost 1.51 Thanks, Alex #include <boost/noncopyable.hpp> #include <boost/move/move.hpp> #include <boost/thread/future.hpp> #include <boost/thread/thread.hpp> using namespace boost; class A : public noncopyable { BOOST_MOVABLE_BUT_NOT_COPYABLE(A) public: A(int i) {} A(BOOST_RV_REF(A) other) {} A& operator=(BOOST_RV_REF(A) other) {} }; A create_a() { return A(42); } unique_future<A> async_create_a() { packaged_task<A> task(create_a); unique_future<A> result = task.get_future(); thread(move(task)).detach(); return move(result); } int main() { A a = async_create_a().get(); return 0; } -- Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org)

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Re: [Boost-users] [graph] problem with weight_map ? (brandes_betweenness_centrality)
by The Maschine 20 Mar '13

20 Mar '13

Hi, ## > EdgeWeightProperty weight = getWeight(a, b); // 0f ... 2.0f Can you just assign a double to a boost::property<...> object? That should probably not be allowed. ## I found the example here and made my code: http://programmingexamples.net/wiki/CPP/Boost/BGL/DijkstraUndirected ### What happens if you write an explicit loop over all of the edges and use put(edge_weight, g, e) directly? Does that change any of the results? -- Jeremiah Willcock ### In not sure what you mean? Im not a super expert, can you please explain your thought more? Best, Tasos

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Boost Geometry Compilation Errors
by Joel Markham 20 Mar '13

20 Mar '13

Trying to use the boost geometry library. Have a very simple example from the boost geometry home page int main(int argc, const char * argv[]) { double points[][2] = {{2.0, 1.3}, {4.1, 3.0}, {5.3, 2.6}, {2.9, 0.7}, {2.0, 1.3}}; bgm::polygon<bgm::d2::point_xy<double> > poly; bg::append(poly, points); boost::tuple<double, double> p = boost::make_tuple(3.7, 2.0); std::cout << "Point p is in polygon? " << std::boolalpha << bg::within(p, poly) << std::endl; … } When trying to build on my Mac I get compiler warnings: point_type.hpp No matching function for call to 'assertion_failed" coordinate_type.hpp No matching function for call to 'assertion_failed" convert_point_to_point.hpp Call to function 'get that is neither visible in the template definition or found… access.hpp Nom member named 'get in boost::geometry::core_dispatch… Is there something wrong with the boost libraries installed via macports?

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[BGL] Dijkstra/A* with large graph
by Nicholas Mario Wardhana 20 Mar '13

20 Mar '13

Hi all, I am wondering if with Boost Graph Library, I can do either of these two things: 1) Merge several small graphs into one large graph 2) Save and load only a portion of a large graph at a time? So the background is as follows. I have a large geometric graph (i.e. a graph with 3D coordinate custom vertex properties), which I want to use for path planning. The graph can be too large to be stored in the memory (if I understand correctly, BGL uses STL data structures, which have limits for the number of elements), so I implement the large graph as multiple small graphs (let's just call them mini-graphs). This way, I can save the mini-graphs to hard-disk, and load only the necessary mini-graphs to plan the path (I have cost function to determine the mini-graphs using Dijkstra). The problem is, this breaks the connectivity of the original graph, and I also have to add some points to two mini-graphs. Running Dijkstra/A* is consequently not straightforward, since the starting and the goal nodes can be in different mini-graphs. The two aforementioned solutions can be used as a workaround. Using approach #1, I can combine the chosen mini-graphs into one, on which I can directly run Dijkstra/A*. In approach #2, I just have one variable of graph, while the mini-graphs can just be implemented as extra properties of the nodes and edges. This way, I can select which nodes and edges to load from the files (e.g. if a node has a mini-graph ID of 1, load the node). Having said that, I don't know how to implement those approaches with BGL. It seems to me that subgraph provides a hierarchically structured graph, but is it possible to just load a subgraph without loading the whole graph? BTW, I am wondering if BGL has an external memory variant, like Parallel BGL for multi-core environment? If not, is anybody aware if there is such library (preferrably free to use for research purpose)? Thank you! Best regards, Nicholas Mario Wardhana

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