July 2002 - Boost-users - lists.boost.org

boost::shared_ptr and stl algorithms
by Bill Eidson 15 Apr '05

15 Apr '05

std::vector< boost::shared_ptr<T> > TVec; I want to write a function object to run std::for_each. to do somework against members of T and accumulate results in functor. My attempts have failed in VC7 with memory errors in my operator() method. struct fo { bool operator()( boost::shared_ptr<T>& t ) { return true; } }; Thanks in advance bille

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BGL and reversing / moving edges
by joshrose 17 Dec '03

17 Dec '03

G'day, I was hoping someone might be able to tell me if they've run into any situations using BGL where they needed to move (or reverse (i.e. flip the source and target)) an edge within a graph implemented as an adjacency_list. I'm working on an implementation of an algorithm for max. weight bipartite matching ("the assignment problem"), and one of the assumptions in the algorithm is that non-matched edges are directed from one subgraph, A, to the other subgraph, B, and matched edges are directed the other way. Over the course of growing the matching, a simple way to add and remove edges from the candidate set is just to reverse the edge, thus the need for some way to reverse the edge within BGL. I don't think I can just remove and then re-add the edge in the other direction, primarily because doing so will (I believe) invalidate any edge_descriptors referring to that edge. In particular, there are property maps keeping track of the weight of edges, the predecessors of certain nodes, etc. that use edge descriptors as keys. I've spent a fair bit of time reading the documentation and looking through the implementation of adjacency_lists (incl. edge_list_impl), and I'm not really sure of a way to either move an edge directly within a graph, or even to create a new edge from another s.t. they have the same edge_descriptor (in general a bad thing, probably). Anyone have any thoughts on this? Thanks, -Josh

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bug report: boost::tokenizer with VC6
by Navi Singh 09 Feb '03

09 Feb '03

The boost release 1.28.0 of the tokenizer library has the following problem: There are 5 examples, namely, simple_example_1.cpp thru simple_example_5.cpp If I change the main() in each of the 5 to to main1() thru main5() and return 0; the vc60 compiler generates an internal compiler error when parsing the file boost\iterator_adapters.hpp on line 869, where it is parsing the following lines: reference operator*() const { return policies().dereference(*this); }

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Q: Graphs. Sorting edges. Possible? How to?
by stas_fomin 07 Nov '02

07 Nov '02

Hello. I a newbie in BGL and I rewrite my LEDA code now... I have to sort (order) edges according to some functor. For example (simplified): typedef adjacency_list<vecS, vecS, bidirectionalS> MyGraph; typedef graph_traits < MyGraph >::edge_descriptor MyGraphEdge; typedef graph_traits < MyGraph >::edge_iterator MyEdgeIter; class MyCompareEdges{ public: bool operator()(MyGraphEdge e1, MyGraphEdge e2) const { return true; } }; .... { MyGraph Gr(10); MyEdgeIter ei_beg, ei_end; MyCompareEdges comp; tie(ei_beg, ei_end) = edges(Gr); std::sort(ei_beg, ei_end, comp); //Error C2676 } And I have error C2676 (below the message...). Questions: 1. Is it possible to sort edges in the graph? 2. How to... Thanks all in advance... Stas Fomin. P.S. vecS, setS, listS for edge container... - C2676. ------------------------------ d:\projects\lib\cpp_libs\libboost\boost\iterator_adaptors.hpp(264) : error C2676: binary '+=' : 'class std::list<struct boost::list_edge<unsigned int,struct boost::no_property>,class std::allocator<struct boost::list_edge<unsigned int,struct boost:: no_property> > >::iterator' does not define this operator or a conversion to a type acceptable to the predefined operator d:\projects\lib\cpp_libs\libboost\boost\iterator_adaptors.hpp (911) : see reference to function template instantiation 'void __thiscall boost::default_iterator_policies::advance(struct boost::iterator_adaptor<class std::list<struct boost::lis t_edge<unsigned int,struct boost::no_property>,class std::allocator<struct boost::list_edge<unsigned int,struct boost::no_property> > >::iterator,struct boost::detail::undirected_edge_iter_policies,class boost::detail::edge_desc_impl<struct boost::b idirectional_tag,unsigned int>,class boost::detail::edge_desc_impl<struct boost::bidirectional_tag,unsigned int>,class boost::detail::edge_desc_impl<struct boost::bidirectional_tag,unsigned int> *,struct boost::multi_pass_input_iterator_tag,int> &,i nt)' being compiled Error executing cl.exe.

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[BGL] How to change the type of vertex_descriptor??
by Erik Arner 14 Sep '02

14 Sep '02

Hi, I have a BGL graph in the following manner: typedef adjacency_list < vecS, vecS, directedS, no_property, property <edge_weight_t, int, property <edge_weight2_t, double> > > Graph; I also have: typedef graph_traits<Graph>::vertex_descriptor Vertex; Now, the default vertex_descriptor seems to be unsigned int. How do I change this to int? Also, where (in which file) is the default set? On another note: the online reference manual is pretty good in my opinion, but it's hard to get a real overview of the contents. It also lacks an index, making it hard to look up questions like the one above. Is the book any better in this respect? Any other references worth looking up - books or webpages? Thanks, Erik

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[BGL] Problem with kevin-bacon sample
by Nicolas Guilhot 14 Sep '02

14 Sep '02

Hi all, I compiled the kevin-bacon sample on a linux box without any problem, but when I try to run the program, I obtain an error output instead of what is expected. Any help would be appreciated. Here is the output off the program : kevin-bacon: /boost_1_27_0/boost/token_iterator.hpp:75: void boost::detail::tokenizer_policy<Type, TokenizerFunc>::increment (Iterator &) [with Iterator = boost::iterator_adaptor<boost::detail::token_iterator_base<const char *>, boost::detail::tokenizer_policy<basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> >, boost::char_delimiters_separator<char, string_char_traits<char> > >, basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> >, const basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> > &, const basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> > *, forward_iterator_tag, ptrdiff_t>, Type = basic_string<char, string_char_traits<char>, __default_alloc_template<true, 0> >, TokenizerFunc = boost::char_delimiters_separator<char, string_char_traits<char> >]: Assertion `b.base().valid_' failed. Abandon Thanks for any answer. Nicolas

2 1

regex performance
by Paul Dubuc 17 Aug '02

17 Aug '02

I'm doing some performance comparisons between Rogue Wave's Regexp class (http://www.roguewave.com/support/docs/tlsref/rwcregexp.cfm) and boost::regex using simple expressions like "^metal.*" and "[0-9]+" with regex_search(). regex is slower by a factor of 6, measuring cpu time (on a SunBlade 100 runing Solaris 8). Is there anything I can do to speed it up? I tried using different values of boost::regbase::flag_type_ to adjust how the regular expressions are interpreted, but with little effect. Any other ideas? (I'm using boost_1_27_0.) Thanks, -- Paul M. Dubuc

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uBLAS Observation: terrible execution speed for prod(matrix,prod(matrix,prod(matrix,matrix)))
by Walter Bowen 05 Aug '02

05 Aug '02

Hi, I am new to uBLAS. I am looking to see if it will be useful for my application (I develop 6-Degrees-of-freedom flight simulations used to analyze avionics systems.) I have benchmarked a few lines of code with RogueWave's Math.h++ (testing for execution speed) and made the following observation. Observation 1) For matrix products of two small (~3-by-3) matrices ( i.e., prod(smallMat1, smallMat2) ) uBLAS executes MUCH FASTER than Math.h++. Observation 2) For matrix produces of two large matrices (100 by 100) uBLAS and Math.h++ give similar execuation speed. Obervation 3) (This is the kicker...) for strung-together matrix products like "Mat1 * Mat2 * Mat3 * Mat4 * Mat5", which I am implementing as "prod(Mat1, prod(Mat2, prod( Mat3, prod(Mat4,Mat5) ) ) ) Math.h++ is MUCH MUCH FASTER than uBLAS. -- by ~2 orders OF MAGNITUDE! I believe that this is a characteristic of the scalability of template expressions. My question is this: Is there a way I an instruct uBLAS not to use template expressions when for strung-together matrix products? Regards, Walt

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collection container
by Bohdan 01 Aug '02

01 Aug '02

Has boost any plans on creating container, that holds data by pointer, not by value? Rationale: It is impossible to use normally vector<...> for types that do not have copy constructor. Interface of vector< shared_ptr<...> > doesn't seems to be very convenient( for example with std::algorithms ). And most of all it is not good idea to show vector< shared_ptr<...> > interface to user of my lib, that wants to have container::iterator with normal behavior. AFAIK majority of existing libraries have/need such container ? As to me it is strange that neither stl nor boost have such class. I'm missing 'something' and there are important reasons for not doing this ?

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Creating groups of regular expressions
by cyndi_r2002 01 Aug '02

01 Aug '02

Hi, I have started using Regex++ and like it a lot but is there a way to use grouping constructs using Regex++ / any alternative that would provide the same functionality? Thanks, Cyndi

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