December 2011 - Boost-users

[BGL] Issue using connected_components
by Nicolas Saunier 07 Dec '11

07 Dec '11

Hi, here is a simplified code sample that I cannot get to work. I use bundled properties for an undirected graph and I do not find what should be the type of the component map (or property map) that should be passed as the second argument of the connected_components function. The sample is useless since only integers are for vertices. #include <boost/graph/adjacency_list.hpp> #include <boost/shared_ptr.hpp> #include <boost/graph/connected_components.hpp> using namespace boost; using namespace std; struct FeatureTrajectory { int id; }; struct FeatureConnection { float minDistance; float maxDistance; }; struct VertexInformation { shared_ptr<FeatureTrajectory> feature; }; typedef adjacency_list < listS, listS, undirectedS, VertexInformation, FeatureConnection> FeatureGraph; int main() { FeatureGraph g; FeatureGraph::vertex_descriptor u, v; FeatureGraph::edge_descriptor e; u = add_vertex(g); v = add_vertex(g); bool unused; tie(e, unused) = add_edge(u, v, g); g[e].minDistance = 0.; g[e].maxDistance = 1.; g[u].feature = shared_ptr<FeatureTrajectory>(new FeatureTrajectory()); g[u].feature->id =11; g[v].feature = shared_ptr<FeatureTrajectory>(new FeatureTrajectory()); g[v].feature->id =12; cout << num_vertices(g) << " " << num_edges(g) << endl; vector_property_map< graph_traits<FeatureGraph>::vertices_size_type > components(num_vertices(g)); int num = connected_components(g, &components[0]); return 0; } The final error is: /usr/include/boost/graph/connected_components.hpp:46: error: no matching function for call to ‘put(long unsigned int*&, void*&, long unsigned int&)’ Can someone help me get it to work and to understand property maps? Thanks! Nicolas -- Nicolas Saunier, ing. jr, Ph.D. Professeur Adjoint / Assistant Professor Département des génies civil, géologique et des mines (CGM) École Polytechnique de Montréal http://nicolas.saunier.confins.net

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Boost.Math and Math Constants
by Paul A. Bristow 07 Dec '11

07 Dec '11

Boost.Math has always had an inconspicuous collection of useful math constants, mainly those that are used internally. The presentation of these was as a function-template, called for example, as pi<double>(). using namespace boost::math::constants; return pi<Real>() * r * r; This leads to some rather ugly equations and is most unpopular with scientific and engineering users. John Maddock has now added a new cunning feature that allows the vast majority of users who just want a built-in double to get the constants quickly as plain variables. So in non-template code, users can write using boost::math::double_constants; double area = pi * r * r; and users can read the equations easily. (Float and long double are similarly available in their own namespaces). The original mechanism which can be used for higher multiprecision user-defined floating-point types appears unchanged but has been improved to work better with UDTs and high precision types. Some draft detailed docs about just these new proposals are at http://boost-sandbox.sourceforge.net/libs/math_constants/doc/html/index.html We would like to be sure that 1 This additional mechanism of presenting constants is acceptable. 2 It is acceptable to add more constants (current new list is about 60 constants). Are there important constants that you think we have missed? Do we need a mini-review? Other views? Paul PS 1 Are there important constants that you think we have missed? 2 Please tell me of mistakes and typos in the draft docs. --- Paul A. Bristow, Prizet Farmhouse, Kendal LA8 8AB UK +44 1539 561830 07714330204 pbristow(a)hetp.u-net.com

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[range] discrepancy between size and vector ::size
by giecrilj＠stegny.2a.pl 07 Dec '11

07 Dec '11

The following code gives me a warning: void trigger (::std ::vector < int > const &v) { ::boost ::size (v) == v. size (); } and the warning is "signed and unsigned in comparison". I understand that (size == end - begin) and that the latter expression is a difference; however, isn't the difference guaranteed to be positive? Also note that no range function ever uses range_size ::type. I suggest that ::boost ::size should return range_size ::type. Chris

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How to pass additional arguments to a boost test case?
by Marc Magrans de Abril 07 Dec '11

07 Dec '11

Dear colleagues, I would like to pass additional command line arguments to a given boost test. For example, if I execute the following from the command line: mytest.exe --log_level=all --param1=value1 --param2=value2 then I would like to be able to get param1 and param2 parameters inside the test cases doing: BOOST_AUTO_TEST_CASE(read_ param_from_command_line) { std::cout << "Param1=" << some_function("param1") << std::endl; std::cout << "Param2=" << some_function("param2") << std::endl; } What s the recommended approach in this case? Thanks, marc

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signature discrepancy between equal_range and upper_bound
by giecrilj＠stegny.2a.pl 06 Dec '11

06 Dec '11

The algorithm equal_range takes the Value by constant reference while the algorithm upper_bound takes Value by value. Why is that? (Note that standard algorithms take a constant reference.)

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[Units] How do you declare a plane angle to be dimensionless?
by Stephen Torri 06 Dec '11

06 Dec '11

Boost ver: 1.45 Compiler: Visual Studio 2008 I am trying to figure out how to declare a plane angle to be dimensionless. In the code I have so far I am using: typedef boost::units::make_system<radii_base_unit, minute_base_unit, boost::units::angle::radian_base_unit >::type myproject_system_t; I have one velocity in radii^1.5/min and a second velocity in radian/min. When I divide the radii^1.5/min by radian/min I am expecting to see radii to be the final dimension. What I am seeing is the denominator has radians in it. Here is my equation ke = radii^1.5/min n = radian/min a1 = ( ke / n ) ^ (2/3) The 'min' dimension cancel out so I am left with radii^1.5/radian before applying the power of 2/3. Applying the power of 2 I see the units are radii^3/radian^2 and then the 1/3 to get a final of radii/radian^(2/3). According to the almighty Wikipedia the radian angle is a dimensionless term. I am wondering what is the recommended course of action I should be taking here? Stephen

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[function] How to use function with templated member functions
by Christian Henning 06 Dec '11

06 Dec '11

Hi there, I would like to boost::function with a templated member function. Please consider the following code: struct my_reader { my_reader(bool full) { if( full ) { _read_function = &my_reader::read_full<int>; } else { _read_function = &my_reader::read_partial<int>; } } void read() { _read_function(this); } private: template< typename T > void read_full() { std::cout << "reading full image" << std::endl; } template< typename T > void read_partial() { std::cout << "reading partial image" << std::endl; } boost::function<void (my_reader*)> _read_function; }; int main(int argc, char* argv[]) { my_reader r(false); r.read(); return 0; } This doesn't compile with Visual Studio 2010 since the compiler cannot: "cannot convert from 'overloaded-function' to 'boost::function<Signature>'" Is there is way to make this happen? Regards, Christian

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Using boost::asio::io_service with boost::packaged_task
by Kelvin Chung 05 Dec '11

05 Dec '11

I'm trying to create a thread pool / task queue like system via boost::asio::io_service and boost::packaged_task rather than attempt to make 800+ threads for 800+ tasks that I have to make. (I'm not sure of the various concurrency issues that I might have, so reducing thread creation overhead is probably one of my big refactorings in my project.) A cursory glance from various sources reveals that I could do something like the following: template <class Ret> class TaskWrapper { // Wrapper around a boost::shared_ptr<boost::packaged_task<Ret>>, as boost::asio::io_service::post() // requires copyable input boost::shared_ptr<boost::packaged_task<Ret>> task; boost::unique_future<Ret> future; public: TaskWrapper(boost::shared_ptr<boost::packaged_task<Ret>>& task_) : task_(task) {} void operator()() { (*task)(); } boost::unique_future<Ret> get_future() { return future; } }; class TaskQueue { boost::asio::io_service io_service; boost::asio::io_service work; boost::thread_group threads; void run() { io_service.run(); } public: TaskQueue(std::size_t size = boost::thread::hardware_concurrency()) : work(io_service) { for (std::size_t i = 0; i < size; ++i) { // Create threads in pool threads.create_thread(boost::bind(&TaskQueue::run, this)); } } ~TaskQueue() { io_service.stop(); threads.join_all(); } template<class Ret> boost::unique_future<Ret> schedule(TaskWrapper<Ret>& task) { io_service.post(boost::bind(&TaskWrapper<Ret>::operator(), boost::ref(task))); return task.get_future(); } }; There are a few questions that I'd like to ask with this: * Would you recommend this? * To retrieve the results, I'd still have to extract all the futures (from TaskQueue::schedule() returns) into a list of boost::shared_futures, and then call boost::wait_for_all() on the list, right? * If a TaskWrapper itself posts other tasks, would a priority inversion or resource starvation issue occur (I keep thinking that it will, for some reason). How should I address this?

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[BGL] clear_vertex in subgraph
by Avishay Ben Shabtai 05 Dec '11

05 Dec '11

> > > According to Ticket #4753 <https://svn.boost.org/trac/boost/ticket/4753> clear > vertex should work on subgraph BUT according to documentation clear_vertex > should remove all edges of specified vertex but in the boost 1.47 > implementation of clear_vertex of subgarph it removes only the out_edges() > is there a prbolem with documentation or the issue was not fixed? > > The code of subgraph is: > > template <typename G>void > clear_vertex(typename subgraph<G>::vertex_descriptor v, subgraph<G>& g) { > while (true) { > typedef typename subgraph<G>::out_edge_iterator oei_type; > std::pair<oei_type, oei_type> p = out_edges(v, g); > if (p.first == p.second) break; > remove_edge(*p.first, g); > } > } > > Thanks > > Avishay > >

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lexical_cast<uint_value_t<10>::least>("7") = 55
by Nathan Ridge 05 Dec '11

05 Dec '11

Whoops! uint_value_t<10>::least is unsigned char... Can something be done about this, like having uint_value_t<10>::least be something that looks and acts like an unsigned char but is recognized by lexical_cast to be an integer type, not a character type?

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