March 2009 - Boost-users - lists.boost.org

selecting a type (tag) based on a runtime enum value
by Hicham Mouline 24 Mar '09

24 Mar '09

Hello, I have a templated function Engine, that takes 3 template arguments, these are tags T1, T2, T3, T4. I have an typedef enum { e1, e2, e3, e4 } E to element ei corresponds the type Ti ... const E e // switch (e) { case e1: Engine< Metafct1<T1>::type, Metafct2<T1>::type, Metafct3<T1>::type >::Process( .... ); break; case e2: Engine< Metafct1<T2>::type, Metafct2<T2>::type, Metafct3<T2>::type >::Process( .... ); break; ... } Is there a shorter way of writing this... For now I only have 4 in the enum, but I may have more later? regards,

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Seg fault while adding 2nd edge to the graph
by Phani Deepak 24 Mar '09

24 Mar '09

hi, i started using BGL for my project. strangely all the examples i tried to learn BGL worked fine. But when i write the actual code for my project, it started giving me this error. Problem: While adding second edge to the boost graph using boost::add_edge(u,v,g) it is giving out a seg fault. Please help with this prob. Iam also attaching the code that's giving the error /*********Code that's giving this error****************/ #include<iostream> #include<vector> #include<string> #include<queue> #include<stdlib.h> #include<string> #include<sstream> #include<boost/graph/graph_traits.hpp> #include<boost/graph/adjacency_list.hpp> class Node{ public: std::string id; double Energy; Node() {} }; class EdgeProperties { public: int targetI; int sourceI; EdgeProperties(int s,int t):sourceI(s),targetI(t) { } }; typedef boost::adjacency_list<boost::listS,boost::listS,boost::bidirectionalS, Node *,EdgeProperties *> Graph; typedef boost::graph_traits<Graph> GraphTraits; typedef GraphTraits::vertex_descriptor Vertex; typedef GraphTraits::edge_descriptor Edge; namespace boost { Vertex getVertexbyId(std::string id,Graph g){ std::cout << "getVID called for " << id << std::endl; fflush(stdout); GraphTraits::vertex_iterator vstart,vend; for(boost::tie(vstart,vend) = boost::vertices(g); vstart!=vend; vstart++) { if(g[*vstart]->id == (id)) return *vstart; } std::cout << "Critical Error: |" << id << "| referencing node not present in graph " << std::endl; return NULL; } } int main(){ Graph g; // populate Graph with all the vertices and edges. std::cout << "* Populating graph with Vertices and Edges " << std::endl; fflush(stdout); Vertex v = boost::add_vertex(g); g[v] = new Node(); g[v]->id = "xor_1"; g[v]->Energy = 2.3; std::cout << "Inserted xor_1" << std::endl; fflush(stdout); v = boost::add_vertex(g); g[v] = (new Node()); g[v]->id = "and_1"; g[v]->Energy = 1.9; std::cout << "Inserted and_1" << std::endl; fflush(stdout); v = boost::add_vertex(g); g[v] = (new Node()); g[v]->id = "i_1"; std::cout << "Inserted i_1" << std::endl; fflush(stdout); // add Edges std::pair<Edge,bool> e; EdgeProperties *ep = new EdgeProperties(1,1); e = boost::add_edge(boost::getVertexbyId("i_1",g),boost::getVertexbyId("and_1",g),ep,g); std::cout << "Inserted Edge 1" << std::endl; fflush(stdout); ep = new EdgeProperties(1,2); e = boost::add_edge(boost::getVertexbyId("i_1",g),boost::getVertexbyId("xor_1",g),ep,g); std::cout << "Inserted Edge 2" << std::endl; fflush(stdout); } /*******************************************************/ - Phani.

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[Q] better 'typedef'
by V S P 24 Mar '09

24 Mar '09

I have read somewhere that boost provides a better typedef. Something that allows to use the 'underlying class' but it is not a macro for example I want to define typedef std::wstring cvarchar_t to use for ODBC/Unicode db access (on win32) and then specialize some templates for this type that would behave differently then wstring I cannot remember what that mechanism was called. Also, sorry, for mixing this question in: is UTF-8 a more 'standard' encoding if I want to interface from my C++/boost programs to ODBC and to Boost.Python on Windows and FreeBSD (I have problems figuring out how to support the difference between UTF-16 on windows/wstring and Unix UTF-32 wstring ... while the unicode ODBC drivers are all 2-byte strings) thanks in advance -- V S P toreason(a)fastmail.fm -- http://www.fastmail.fm - Same, same, but different...

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proper erasing from ptr_vector
by Archie14 23 Mar '09

23 Mar '09

I have ptr_vector<A> lst; When I need to erase element from this container - should I just do A* el; iterator it = std::find (lst.begin(), lst.end(), el); lst.erase(it); or A* el; iterator it = std::find (lst.begin(), lst.end(), el); delete lst.erase(el);

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[iterator] unrelated type problem with iterator_facade arrow operator
by Michael Fawcett 23 Mar '09

23 Mar '09

Can someone confirm if the attached code doesn't compile intentionally or if this is a bug? I'm sorry for not posting a minimal example but I couldn't figure out how to reduce the problem. It requires Windows (uses ATL::CAdapt and ATL::CComBSTR) and I've tested using VS 2005 and VS2008. This bug manifests when the Reference type has overloaded the address-of operator to return a type not implicitly convertible to Value * (I believe). Changing lines 324-326 in iterator_facade.hpp from: static type make(Reference x) { return implicit_cast<type>(&x); } to: static type make(Reference x) { return implicit_cast<type>(boost::addressof(x)); } and adding the appropriate include makes the attached code compile. Full error log below: 1>c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_facade.hpp(326) : error C2664: 'boost::implicit_cast' : cannot convert parameter 1 from 'BSTR *' to 'ATL::CComBSTR *' 1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast 1> c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_facade.hpp(325) : while compiling class template member function 'ATL::CComBSTR *boost::detail::operator_arrow_result<ValueType,Reference,Pointer>::make(Reference)' 1> with 1> [ 1> ValueType=ATL::CComBSTR, 1> Reference=ATL::CComBSTR &, 1> Pointer=ATL::CComBSTR * 1> ] 1> c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_facade.hpp(641) : see reference to class template instantiation 'boost::detail::operator_arrow_result<ValueType,Reference,Pointer>' being compiled 1> with 1> [ 1> ValueType=ATL::CComBSTR, 1> Reference=ATL::CComBSTR &, 1> Pointer=ATL::CComBSTR * 1> ] 1> c:\dev\vendor\boost\1.37.0\boost\iterator\iterator_adaptor.hpp(271) : see reference to class template instantiation 'boost::iterator_facade<Derived,Value,CategoryOrTraversal,Reference,Difference>' being compiled 1> with 1> [ 1> Derived=test::atl::CAdapt_iterator<std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>>>, 1> Value=ATL::CComBSTR, 1> CategoryOrTraversal=std::random_access_iterator_tag, 1> Reference=ATL::CComBSTR &, 1> Difference=__w64 int 1> ] 1> c:\dev\personal\boost\iterator_adaptor_bug\main.cpp(65) : see reference to class template instantiation 'boost::iterator_adaptor<Derived,Base,Value,Traversal,Reference>' being compiled 1> with 1> [ 1> Derived=test::atl::CAdapt_iterator<std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>>>, 1> Base=std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>>, 1> Value=ATL::CComBSTR, 1> Traversal=std::random_access_iterator_tag, 1> Reference=ATL::CComBSTR & 1> ] 1> c:\dev\personal\boost\iterator_adaptor_bug\main.cpp(103) : see reference to class template instantiation 'test::atl::CAdapt_iterator<Iterator>' being compiled 1> with 1> [ 1> Iterator=std::_Vector_iterator<ATL::CAdapt<ATL::CComBSTR>,std::allocator<ATL::CAdapt<ATL::CComBSTR>>> 1> ] Thanks for any insight, --Michael Fawcett

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Re: [Boost-users] Dijkstra shortest path
by Florian.PONROY＠fr.thalesgroup.com 23 Mar '09

23 Mar '09

Hi, The following algorithm should do the trick: // predecessors is the predecessor map // destinationNode is the node you want to reach // sourceNode is the source of the graph int currentNode = destinationNode; int predecessorNode = 0; std::cerr << boost::format("--- PATH: %d <- ") % destinationNode; do { predecessorNode = predecessors[currentNode]; if (predecessorNode == currentNode) { // Unreachable nextHop = 0; std::cerr << "XXX" << std::endl; break; } else if (predecessorNode == sourceNode) { // Next hop found nextHop = currentNode; std::cerr << sourceNode << std::endl; break; } else { // One hop on the path currentNode = predecessorNode; std::cerr << boost::format("%d <- ") % currentNode; } } while (true); Hope it helps, Florian -----Message d'origine----- De : boost-users-bounces(a)lists.boost.org [mailto:boost-users-bounces@lists.boost.org]De la part de dwaem Envoyé : lundi 23 mars 2009 16:23 À : boost-users(a)lists.boost.org Objet : Re: [Boost-users] Dijkstra shortest path Steven Watanabe-4 wrote: > > AMDG > > dwaem wrote: >> int weight[] = {1, 1, 2, 2, 3, 4, 3, 4, 5, 6, 7}; >> >> <snip> >> >> it shows >> distances and parents: >> distance(A) = 0, parent(A) = C >> distance(B) = 0, parent(B) = A >> distance(C) = 0, parent(C) = C >> distance(D) = 0, parent(D) = C >> distance(E) = 0, parent(E) = C >> >> >> which makes no sense. >> > > You're not using the weight array anywhere, > so you get the default weight of 0 for every edge. > > In Christ, > Steven Watanabe > > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users > > Yes this is my obviouse oversight. But now when I have founded shortest path from node A to node B. How to display full path from A to B, not only parent of the last node. -- View this message in context: http://www.nabble.com/Dijkstra-shortest-path-tp22626827p22662345.html Sent from the Boost - Users mailing list archive at Nabble.com. _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

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Dijkstra shortest path
by dwaem 23 Mar '09

23 Mar '09

Hi I made a little change to example from manual which search shortest path http://www.boost.org/doc/libs/1_37_0/libs/graph/example/dijkstra-example.cpp http://www.boost.org/doc/libs/1_37_0/libs/graph/example/dijkstra-example.cpp by adding add_edge function but is seams to give incorect results #include <boost/config.hpp> #include <algorithm> #include <vector> #include <utility> #include <iostream> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/reverse_graph.hpp> #include <boost/graph/graph_utility.hpp> #include <boost/graph/dijkstra_shortest_paths.hpp> #include <boost/graph/graph_traits.hpp> #include <boost/graph/adjacency_list.hpp> using namespace boost; int main() { typedef adjacency_list < vecS, vecS, bidirectionalS, no_property, property < edge_weight_t, int > > graph; typedef graph_traits < graph >::vertex_descriptor vertex_descriptor; typedef graph_traits < graph >::edge_descriptor edge_descriptor; graph G(5); enum nodes { A, B, C, D, E }; add_edge(A, E, G); add_edge(B, E, G); add_edge(C, E, G); add_edge(A, B, G); add_edge(B, D, G); add_edge(B, A, G); add_edge(B, C, G); add_edge(C, A, G); add_edge(C, D, G); add_edge(D, A, G); add_edge(D, B, G); int weight[] = {1, 1, 2, 2, 3, 4, 3, 4, 5, 6, 7}; char name[] = "ABCDE"; std::cout << "\n"; vertex_descriptor s = vertex(C, G); property_map<graph, edge_weight_t>::type weightmap = get(edge_weight, G); std::vector<vertex_descriptor> p(num_vertices(G)); std::vector<int> d(num_vertices(G)); dijkstra_shortest_paths(G, s, predecessor_map(&p[0]).distance_map(&d[0])); std::cout << "distances and parents:" << std::endl; graph_traits < graph >::vertex_iterator vi, vend; for (tie(vi, vend) = vertices(G); vi != vend; ++vi){ std::cout << "distance(" << name[*vi] << ") = " << d[*vi] << ", "; std::cout << "parent(" << name[*vi] << ") = " << name[p[*vi]] << std::endl; } std::cout << std::endl; } it shows distances and parents: distance(A) = 0, parent(A) = C distance(B) = 0, parent(B) = A distance(C) = 0, parent(C) = C distance(D) = 0, parent(D) = C distance(E) = 0, parent(E) = C which makes no sense. Marcin Matuszak -- View this message in context: http://www.nabble.com/Dijkstra-shortest-path-tp22626827p22626827.html Sent from the Boost - Users mailing list archive at Nabble.com.

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[lambda]How can I call function of objects in std::list while using std::for_each?
by 钱晓明 23 Mar '09

23 Mar '09

Please help me! I want to call a virtual function of objects in std::list while using std::for_each: struct DiscardableItem { void Discard() { std::cout<<"Discard item!"<<std::endl; } }; std::list<DiscardableItem*> items; items.push_back(new DiscardableItem); items.push_back(new DiscardableItem); std::for_each( items.rbegin(), items.rend(), _1->*&DiscardableItem::Discard ); But DiscardableItem::Discard does not be called. How can I make it work? thanks! I think lambda can solve this problem easily.

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[utility] addressof issue with classes having templated conversion operators
by Gevorg Voskanyan 23 Mar '09

23 Mar '09

Hi folks, I've came across a problem with addressof() when the argument is of a class type with a template conversion operator. A minimal test case reproducing the issue is attached. Using boost 1.38, the example fails to compile under gcc 4.2.2, with the following error: ../../../../vendor/boost/boost_1_38_0/boost/utility/addressof.hpp: In function 'T* boost::addressof(T&) [with T = convertible]': addressof_conversion.cpp:17: instantiated from here boost/boost_1_38_0/boost/utility/addressof.hpp:42: error: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: ../../../../vendor/boost/boost_1_38_0/boost/utility/addressof.hpp:26: note: candidate 1: static T* boost::detail::addressof_impl<T>::f(T&, long int) [with T = convertible] ../../../../vendor/boost/boost_1_38_0/boost/utility/addressof.hpp:32: note: candidate 2: static T* boost::detail::addressof_impl<T>::f(T*, int) [with T = convertible] AFAICT gcc is right complaining here, according to 13.3.3 The same example compiles OK with boost 1.33.1, and the changeset that causes the difference seems to be this one: https://svn.boost.org/trac/boost/changeset/44705 Can this be considered a regression? How should this issue be addressed? Thanks, Gevorg

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Suggestion about using Signals2
by Daniele Barzotti 23 Mar '09

23 Mar '09

Hi, I need some help on using signals2 in my app, I hope to explain my problem well. I have a thread that reads from the RS232: void SerialPort::reading() { ... read... if (data_available) signal_OnData; } the signal_OnData is: typedef boost::signals2::signal<void ()> _signal_void; _signal_void signal_OnData; And I connect it to a method MyUserClass::OnDataReceived() Into this method (MyUserClass::OnDataReceived) I need to re-send some data to RS232, but the SerialPort::reading thread is locked because it's waiting the OnDataReceived ends.. In fact, when the methods OnDataReceived ends, I receive data again. How can I solve this problem? Thanks in advance! Daniele.

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