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[range] Best way to construct a std::set from a range?
by Gabriel Redner 08 Mar '10

08 Mar '10

If I have a pair of iterators, I can construct a set like so: std::set<SomeType> s(it1, it2); If instead I have a range, I can adapt it like so: std::set<SomeType> s(boost::begin(range), boost::end(range)); However, my range object is being constructed on the fly. I'd like to be able to do: std::set<SomeType> s(MakeRange(args)); But clearly this is not supported by the library. It seems I need to store the range object in a variable in order to do this, which defeats the syntax-simplifying benefits of using ranges. Can this be avoided? Are there some recommended no-overhead tricks for doing this that achieve a clean syntax? Implicit conversions? Explicit "ToSet" conversion functions? Can boost.assign be of help? (My initial reading of the assign documentation suggests not, but perhaps I'm missing something). I'm also not averse to a macro so long as it looks "language-like," but so far I haven't produced anything satisfactory. Has anyone else wrestled with this one and come out victorious? Thanks, -Gabe

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[mpi] open/write to file for simple output
by alfC 07 Mar '10

07 Mar '10

Hi, I am fairly new to mpi (and boost mpi). I have an mpi program and I need to dump some intermediate and results to a simple text file. First, is there already any good (using boost.mpi or not) to open and write files (let's say from process 0) and write to them. Second, if not, I am already trying to make the code as transparent as possible: I guess the most primitive way to do this is to do something like ofstream ofs(); if(world.rank()==0) ofs.open("file"); ... if(world.rank()==0) ofs<<result<<endl; but the code is full of "if(world.rank()==0)" and worst of all there is a dangling ofs. I tried other possibilities, like making intensive use of boost::optional boost::optional<std::ofstream> optional_ofs(world.rank()==0, std::ofstream("file") ); ... if(optional_ofs) *optional_ofs<<result<<endl; //or optional_ofs? *optional_ofs<<result<<endl; and even activating exceptions for boost optional, in such a way that this makes sense: try{ *optional_ofs<<result<<endl; }catch(...){} and executes only for the process(es) where the stream is actually created. The good thing is that once the stream is created it handles its own existence, regardless of the process number chosen to write to the file. I also looked into boost.interprocess file_lock but it seems it doesn't apply to this case. The third option is more complicated (although I partially implemented it already) by encapsulating this in a class such that the following syntax makes sense for the parallel execution mpi::ofstream ofs("file", world); // class mpi::ofstream is defined somehow, only one process actually opens the file ofs<<result<<endl; //(indirectly only the first process writes to the file This is even more general because (optionally) I can make the result to be printed only once if all processes agree in the results (the value of the variable is common) or different times (or just fail) if the actaul values of result do not agree from all the processes. does this all makes any sense? or I am reinventing the wheel? Also, in my particular cluster, all the processes share the same file system, which I think it is the common case but also the origin of the dilemma. (Note that I am *not* trying to write a file in parallel, I am just trying to print common (gathered) results to a file. nor I am trying to read from a file for the moment) Any advice? Thank you, Alfredo

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Graph Library Random Access Iterators?
by Theodore McCormack 06 Mar '10

06 Mar '10

Hello all, I am trying to iterate through a list of edges in the boost graph library, but i would like to advance more than one at a time or be able to use random access to an edge in the set. For example: Currently, to find the edge at index in the edge set I have to iterate through all the edges: Edge e; int count = 0; for (edge_range_t er = edges(graph); er.first != er.second; er.first++) { e = (*er.first); if (count == index) break; count++; } return e; I would like something like: Edge e; edge_range_t er = edges(graph); e = (*er[index].first); return e; Is there a way to index with iterators? Regards

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[boost-users][git] gitting boost
by Andrey Torba 06 Mar '10

06 Mar '10

Hi all, I prefer git over svn. I use a git clone of boost: origin git://sodium.resophonic.com/boost It had worked perfectly until several months ago it started to return the error on 'git pull' command: fatal: The remote end hung up unexpectedly The same error occurs if i clone git://gitorious.org/boost/svn.git. I use git version 1.6.3.3. How can i git boost? Thanks -- Regards, Andrey

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[program_option] how to say only certain strings are allowed as arguments?
by Thorsten Ottosen 06 Mar '10

06 Mar '10

Hi, Is there some way to say bpo::options_description desc("Allowed options"); desc.add_options() ("method", bpo::value<std::string>()->allowed_values("foo")("bar"), "" ) so I donøt have to reject the arguments manually? Thanks -Thorsten

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[proto] Deep copy question
by Manjunath Kudlur 06 Mar '10

06 Mar '10

Hello, I define the copy constructor for my class and print out out a message when it is called. See the following program. When I have "proto::terminal<Var<int> >::type a", and try to call BOOST_PROTO_AUTO(pr, a), I see that the copy constructor is called two times. Why is the object getting copied twice during the deep copy? When I have "proto::literal<Var<int> > a", I see that the copy constructor is getting called twice during the declaration of 'a' itself, and twice when I try to call BOOST_PROTO_AUTO(pr, a). I was under the impression that objects are held by reference inside expressions. Why are they copied twice in the proto::literal case? Actually, I am looking for some advice on the following: I know that when I have proto::terminal<Var<int> >, the underlying object is created once, and held by reference *everywhere* it is appears in a large complex expression. But as soon as I try to do a deep_copy of the expression (as in BOOST_PROTO_AUTO), the underlying object is copied once for *every* appearance in the expression. How do I make it such the underlying object doesn't copied many times? I want to have the copied expression also to have the property that the original expression had, i.e., everywhere an underlying object is referenced, they all refer to the same object. I will be grateful for any advice. #include <boost/proto/proto.hpp> #include <boost/proto/proto_typeof.hpp> #include <iostream> #include <sstream> #include <string> namespace proto=boost::proto; namespace mpl=boost::mpl; template<typename VT> struct Var { VT value; Var(const Var<VT> &that) { std::cout << "Copy\n"; value = that.value; } Var() { std::cout << "Default\n"; value = 0; } void assign(const VT v) { value = v; } }; typedef proto::literal<Var<int> > int32_; //typedef proto::terminal<Var<int> >::type int32_; int main() { int32_ a; std::cout << "Before\n"; BOOST_PROTO_AUTO(pr, (a)); std::cout << "After\n"; } Thanks, Manjunath

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[mpl] defaults with associative sequence
by Manfred Doudar 06 Mar '10

06 Mar '10

Hi, Maybe I am misreading the documentation, but if I have an mpl::map and try and get an element associated with a key all's good, while if I assign a default - I get an error that mpl::at only takes 2 and not 3 template parameters. Simple example for sake of completness: using namespace boost::mpl; typedef map< pair<int, int_<0> > , pair<float, int_<1> > > m; at<m, float>::type::value; // Ok at<m, double, int_<2> >::type::value; // compiler error Indeed a look in boost/mpl/at.hpp even leads me to believe that mpl::at only takes two template parameters (maybe I mistaken), but documentation suggests otherwise. [Compiler: GCC-4.4.2 ; Boost-1.42] Am I doing something blatantly wrong? Cheers, -- Manfred

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Problem with Boost Serialization
by Binh Luong 05 Mar '10

05 Mar '10

Hello, i have some problems with the serialization of boost. I am working now with a program and want to use boost to serialize an object to a xml archive. I have read the tutorials on the homepage and make the necessary steps but still get some errors while compiling: In file included from /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/xml_oarchive.hpp:31, from message/remote/RemoteMessagingSystem.h:30, from message/remote/RemoteMessagingSystem.cpp:1: /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/basic_xml_oarchive.hpp: In member function 'void boost::archive::basic_xml_oarchive<Archive>::save_override(T&, int) [with T = Message* const, Archive = boost::archive::xml_oarchive]': /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/detail/interface_oarchive.hpp:64: instantiated from 'Archive& boost::archive::detail::interface_oarchive<Archive>::operator<<(T&) [with T = Message* const, Archive = boost::archive::xml_oarchive]' /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/detail/interface_oarchive.hpp:72: instantiated from 'Archive& boost::archive::detail::interface_oarchive<Archive>::operator&(T&) [with T = Message*, Archive = boost::archive::xml_oarchive]' message/remote/RemoteMessagingSystem.cpp:147: instantiated from here /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/basic_xml_oarchive.hpp:92: error: no matching function for call to 'assertion_failed(mpl_::failed************ boost::serialization::is_wrapper<Message* const>::************)' In file included from /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/xml_iarchive.hpp:24, from message/remote/RemoteMessagingSystem.h:31, from message/remote/RemoteMessagingSystem.cpp:1: /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/basic_xml_iarchive.hpp: In member function 'void boost::archive::basic_xml_iarchive<Archive>::load_override(T&, int) [with T = Message*, Archive = boost::archive::xml_iarchive]': /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/xml_iarchive.hpp:80: instantiated from 'void boost::archive::xml_iarchive_impl<Archive>::load_override(T&, int) [with T = Message*, Archive = boost::archive::xml_iarchive]' /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/detail/interface_iarchive.hpp:61: instantiated from 'Archive& boost::archive::detail::interface_iarchive<Archive>::operator>>(T&) [with T = Message*, Archive = boost::archive::xml_iarchive]' message/remote/RemoteMessagingSystem.cpp:164: instantiated from here /home/v0d0i/libraries/boost_1_42_0/include/boost/archive/basic_xml_iarchive.hpp:70: error: no matching function for call to 'assertion_failed(mpl_::failed************ boost::serialization::is_wrapper<Message*>::************)' make[2]: *** [RemoteMessagingSystem.o] Error 1 make[2]: Leaving directory `/home/v0d0i/workspace/trunk1/src/base' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory `/home/v0d0i/workspace/trunk1/src' make: *** [all-recursive] Error 1 It seems like there is something wrong with the Wrapper although i have defined the following Wrappers: BOOST_CLASS_IS_WRAPPER(Message*); BOOST_CLASS_IS_WRAPPER(Message* const); BOOST_CLASS_IS_WRAPPER(Message); I also used the boost::serialization::make_nvp for the name-value pairs purpose of xml archive. What am i doing wrong? Thanks, Ngoc Mai

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[utility] swap
by Robert Jones 05 Mar '10

05 Mar '10

I'm sure I'm being a bit dense here, but apart from handling native arrays what does boost::swap give you that std::swap doesn't? Thanks, - Rob.

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BGL using the VertexIndexMap with VertexList=listS
by khaled 05 Mar '10

05 Mar '10

Hello I'm using the BGL and wandering to use dijkstra_short_path I this code struct vertex1 { int step; int node; int MPI; int OMP; int acc; }; struct edge1 { double cost; }; typedef boost::adjacency_list< boost::listS, boost::listS, boost::directedS, vertex1, edge1> Graph; Graph g; std::vector<double> distances(num_vertices(g)); dijkstra_shortest_paths(g, from, weight_map(get(&edge1::cost, g)) .distance_map(make_iterator_property_map(distances.begin(), get(vertex_index, g)))); I have a problem with the VertexIndexMap (I guess is this the problem :) ) as I'm using a adjacenty_list with VertexList=listS does not have an internal vertex_index property. So, Please can you help me to fix this ? what is the VertexIndexMap to be used with the listS VertexList ?? Thanks -- K.H

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