December 2011 - Boost-users

[BGL] getting an edge_descriptor of a reverse_graph
by Alex Hagen-Zanker 06 Jan '12

06 Jan '12

I upgraded from boost 1.45 to 1.48 and there are some breaking changes related to reverse_graph The main problem that I encounter is that boost::edge(u ,v, graph) returns a edge_descriptor to the graph that underlies reverse_graph, rather than reverse_graph itself . The following therefore does not compile: template<typename Graph> void foo(Graph& graph) { boost::graph_traits<Graph>::edge_descriptor e = boost::edge(0, 1, graph).first; } int main() { boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS> graph(2); foo(graph); // this line compiles foo(boost::make_reverse_graph(graph)); // this line does not compile } Do you have suggestions how to rewrite foo(Graph& graph) in order to generically work for both plain and reversed graphs? For now I have rewritten the boost::edge function in reverse_graph.hpp to return a pair<reverse_graph_edge_descriptor, bool> but that does not seem right. Thanks, Alex

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Boost::shared::memory consistency
by Josmon Paul 05 Jan '12

05 Jan '12

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[BGL] Finding the descriptor for a given vertex
by Kelvin Chung 05 Jan '12

05 Jan '12

Suppose I have the following: template <class T> class Graph { // Adapter class that I use for my purposes typedef typename boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS, T> innerGraph; typedef typename boost::graph_traits<innerGraph>::vertex_descriptor VertexDescriptor; innerGraph G; public: void addVertex(const T& vertex); bool containsVertex(const T& vertex) const; void addEdge(const T& from, const T& to); // More stuff here }; The intent of this adapter class is to basically abstract out all the mentions of stuff like the descriptors and such. So a good helper function to this end would be a function that retrieves the VertexDescriptor for a given T, if it exists. Is there such a function already in the BGL, or do I have to manage that separately (ie. having an external map)?

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[Phoenix][v3] Argument/State dependent return type of actors?
by Josef Weinbub 05 Jan '12

05 Jan '12

Hi Recently I made myself familiar with Phoenix v3, more specifically with actors. I did a few test implementations, and I wondered if there is a way to access the argument types (nested in the context's environment) and/or the type of the state(s) (nested in the proto expression) for the actor's result type declaration. Have a look at the following actor dummy implementation, especially at the line ''typedef int result_type;'': (for the sake of completeness, the complete actor implementation is provided) ------------------------------------------------------------ BOOST_PHOENIX_DEFINE_EXPRESSION( (boost)(phoenix)(myactor) , (boost::phoenix::meta_grammar) ) struct myactor_eval { // ------------------------ // the result type can not be made dependable from // one of the actors argument types .. it is // typedef int result_type; // ------------------------ template <typename StateExpr, typename Context> result_type operator()(StateExpr const& state_expr, Context & ctx) const { return -1; } }; namespace boost { namespace phoenix { template <> struct default_actions::when< rule::myactor> : boost::phoenix::call< ::myactor_eval> {}; template <typename T> typename expression::myactor<T>::type const inline myactor(T& t) { return expression::myactor<T>::make(t); } }} ------------------------------------------------------------ As I already stated, I wonder if there is a way to have access to the argument and state types for the result type, maybe as it was possible in Phoenix v2 via a nested template struct which got the same template parameters as the functor, like the simple example in the following: ------------------------------------------------------------ struct myactor_eval { template <typename StateExpr, typename Context> struct result { typedef typename result_of::env<Context>::type Environment; typedef typename remove_reference< Environment>::type::args_type Args; typedef typename result_of::value_at_c< Args, 0>::type Parameter; // make the result type argument dependent! typedef typename Parameter::value_type type; }; ... }; ------------------------------------------------------------ I do hope that I haven't overlooked something in the docs, sorry if I did. Thanks for your support! Cheers, Josef Weinbub

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[Container] deque emplace() requirements
by Szymon Gatner 04 Jan '12

04 Jan '12

Hi, question: why container::deque<T>::emplace_back() requires T to be copyable? Shouldn't it just be using placement new operator with passed c-tor params? Unless growing of deque causes elements to be copied which is not what I want at all (hence deque and not vector). Cheers, Simon -- Szymon Gatner The Lordz Games Studio www.thelordzgamesstudio.com

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[phoenix] ambiguity between std::begin/end and phoenix::begin/end due to ADL
by Nathan Ridge 04 Jan '12

04 Jan '12

Hello, I am running into a problem where an unqualified call to begin() on a range type whose template parameters include a Boost.Phoenix type (for examle filtered_range<Pred, R> where Pred is a phoenix function) is ambiguous because, in addition to the intended std::begin, phoenix::begin is being found by ADL. What can be done about this? There exists precedent for placing boost::xxx::begin/end functions in ADL barrier namespaces because C++11 encourages unqualified calls to begin/end (specifically, this was done for boost::range::begin/end). Should the same thing be done for Phoenix? Here is a minimal example that reproduces the problem: #include <iterator> #include <boost/range/adaptor/filtered.hpp> #include <boost/phoenix/phoenix.hpp> using std::begin; int main() { using boost::phoenix::arg_names::arg1; using boost::adaptors::filtered; int v[5]; const auto& f = v | filtered(arg1 < 0); begin(f); } And here are the errors, with GCC 4.7: test.cpp: In function 'int main()': test.cpp:15:12: error: call of overloaded 'begin( const boost::range_detail::filtered_range< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less , boost::proto::argsns_::list2< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal , boost::proto::argsns_::term< boost::phoenix::argument<1> >, 0l > >, boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal , boost::proto::argsns_::term<int>, 0l > > >, 2l > >, int [5] > & )' is ambiguous test.cpp:15:12: candidates are: In file included from string:53:0, from c++/4.7.0/bits/locale_classes.h:42, from ios_base.h:43, [STL Decryptor: Suppressed 3 more STL standard header messages] from test.cpp:1: c++/4.7.0/bits/range_access.h:58:5: decltype ( __cont.begin() ) begin( const boost::range_detail::filtered_range< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost::proto::argsns_ ::list2< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term< boost::phoenix::argument<1> >, 0l> >, boost ::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term<int>, 0l> > >, 2l> >, int [5]>; decltype (__cont.begin()) = boost::filter_iterator< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost::proto::argsns_ ::list2< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term< boost::phoenix::argument<1> >, 0l> >, boost ::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term<int>, 0l> > >, 2l> >, int *> &) c++/4.7.0/bits/range_access.h:48:5: decltype ( __cont.begin() ) begin( const boost::range_detail::filtered_range< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost::proto::argsns_ ::list2< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term< boost::phoenix::argument<1> >, 0l> >, boost ::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term<int>, 0l> > >, 2l> >, int [5]>; decltype (__cont.begin()) = boost::filter_iterator< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost::proto::argsns_ ::list2< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term< boost::phoenix::argument<1> >, 0l> >, boost ::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term<int>, 0l> > >, 2l> >, int *> &) In file included from boost/boost/phoenix/stl/container.hpp:11:0, from boost/boost/phoenix/stl.hpp:16, from boost/boost/phoenix/phoenix.hpp:18, from test.cpp:4: boost/boost/phoenix/stl/container/container.hpp:794:1: const boost ::phoenix::detail::expression::function_eval< boost::phoenix::stl::begin, boost::range_detail::filtered_range< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost::proto::argsns_ ::list2< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term< boost::phoenix::argument<1> >, 0l> >, boost ::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term<int>, 0l> > >, 2l> >, int [5]>; boost::phoenix::detail::expression::function_eval< boost::phoenix::stl::begin, A0>::type = boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::phoenix::detail::tag::function_eval, boost::proto ::argsns_::list2< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost::proto ::argsns_::term<boost::phoenix::stl::begin>, 0l>, boost ::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost::proto ::argsns_::term< boost::range_detail::filtered_range< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost ::proto::argsns_::list2< boost::phoenix::actor< boost::proto::exprns_ ::basic_expr< boost::proto::tagns_::tag ::terminal, boost::proto ::argsns_::term< boost::phoenix ::argument<1> >, 0l> >, boost::phoenix::actor< boost::proto::exprns_ ::basic_expr< boost::proto::tagns_::tag ::terminal, boost::proto ::argsns_::term<int>, 0l> > >, 2l> >, int [5]> >, 0l> >, 2l> > >::type boost::phoenix::begin( const boost::range_detail::filtered_range< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost::proto::argsns_ ::list2< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term< boost::phoenix::argument<1> >, 0l> >, boost ::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost ::proto::argsns_::term<int>, 0l> > >, 2l> >, int [5]>; boost::phoenix::detail::expression::function_eval< boost::phoenix::stl::begin, A0>::type = boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::phoenix::detail::tag::function_eval, boost::proto ::argsns_::list2< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost::proto ::argsns_::term<boost::phoenix::stl::begin>, 0l>, boost ::proto::exprns_::basic_expr< boost::proto::tagns_::tag::terminal, boost::proto ::argsns_::term< boost::range_detail::filtered_range< boost::phoenix::actor< boost::proto::exprns_::basic_expr< boost::proto::tagns_::tag::less, boost ::proto::argsns_::list2< boost::phoenix::actor< boost::proto::exprns_ ::basic_expr< boost::proto::tagns_::tag ::terminal, boost::proto ::argsns_::term< boost::phoenix ::argument<1> >, 0l> >, boost::phoenix::actor< boost::proto::exprns_ ::basic_expr< boost::proto::tagns_::tag ::terminal, boost::proto ::argsns_::term<int>, 0l> > >, 2l> >, int [5]> >, 0l> >, 2l> > &) Thanks, Nate

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property type trait
by Amir Yazdanbakhsh 02 Jan '12

02 Jan '12

Hi, I new to boost graph library. The thing that I have in my mind is to find the type of property that passed to a function and execute something based on that. I implemented two bundled properties each for vertex and edge. I want to implement a general function, say print a property, if the passed property is a vertex property the function should iterate over vertices and print out them and if it's edge property it should iterate over edges. Is it any way to do that? Thanks Best Regards, A. Yazdanbakhsh >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> PhD. Student School of Electrical and Computer Engineering University of Wisconsin-Madison E-mail: yazdanbakhsh(a)wisc.edu <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

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[multi_array]bug in strides calculation with some storage orderings
by Larry Evans 01 Jan '12

01 Jan '12

If I understand correctly, the multi_array storage order determines which strides are larger than others. In short: if( order[I]>order[I+1]) then stride[I]>stride[I+1] However, the output from the attached code shows that this is not always true. In the attached code, the mono_tonic_print function tests the conditions and prints out the results. The following partial output: :count=3 :permut_v={ 1, 2, 0} :permut_i={ 2, 0, 1} :ma.ordering(*)==permut_v=1 :multi_array_strides:strides()={ 12, 1, 3} :monotonically increasing={ 0, 0} :is_mono_tonic=0 :expected_strides:{ 4, 8, 1} :monotonically increasing={ 1, 1} :is_mono_tonic=1 :count=4 :permut_v={ 2, 0, 1} :permut_i={ 1, 2, 0} :ma.ordering(*)==permut_v=1 :multi_array_strides:strides()={ 4, 8, 1} :monotonically increasing={ 0, 0} :is_mono_tonic=0 :expected_strides:{ 12, 1, 3} :monotonically increasing={ 1, 1} :is_mono_tonic=1 shows that the multi_array code fails this monotonic constrait when the order is one of: :permut_v={ 1, 2, 0} :permut_v={ 2, 0, 1} The code also shows a possible solution. This possible solution uses the inverse permutation instead of the original permutation to calculate the strides, as shown in the expected_strides function. There's also a macro, NO_INVERT_PERMUT, which, if defined, has expected_strides reproduce the multi_array strides, which may help narrow down the source of the error in multi_array's stride calculation. The output is also attached. If macro INDENT_OUTPUT is defined, the code requires: http://svn.boost.org/svn/boost/sandbox/variadic_templates/boost/iostreams/f… http://svn.boost.org/svn/boost/sandbox/variadic_templates/boost/iostreams/u… http://svn.boost.org/svn/boost/sandbox/variadic_templates/boost/utility/tra… http://svn.boost.org/svn/boost/sandbox/variadic_templates/boost/utility/ind… If you don't want to download those, then the output will not be nicely indented as shown in the attached output. HTH. -regards, Larry

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iterate over vertices with special propoerty
by Amir Yazdanbakhsh 01 Jan '12

01 Jan '12

Hi, I want to write an iterator which returns the vertices with a special property. For example have an functions which takes a graph and a string and returns an iterator over all the vertices that have this string as their name. Thanks Best Regards, A. Yazdanbakhsh >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> PhD. Student School of Electrical and Computer Engineering University of Wisconsin-Madison E-mail: yazdanbakhsh(a)wisc.edu <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

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[inteprocess] timed_lock absolute time
by Edward Diener 31 Dec '11

31 Dec '11

Is the "absolute time" mentioned when using a mutex and timed_lock a local time or a UTC time ? I am guessing a local time but I just want to make sure.

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