July 2011 - Boost-users - lists.preview.boost.org

Problem with dijkstra_shortest_paths
by Stephen Woodbridge 01 Jul '11

01 Jul '11

Hi all, I am C programmer floundering in a C++ world! I have the function that I call from C that builds a graph, runs dijkstra_shortest_paths(), then extracts the results and passes them back to a C array of structs. Code is in pastebin: http://pastebin.com/xi7vLpTx This seems to work and everything looks ok, EXCEPT the edge ids are not correct. I suspect this is because I'm not doing something correctly and I have been messing with this for a couple weeks without success, so I think its time to ask for help. So in the function: graph_add_edge(G &graph, int id, int source, int target, float8 cost) id is the edge id source is the node id at the start of the edge target is the node_id at the end of the edge cost is the cost to traverse the edge from source to target I would really appreciate it if someone could look at this and point out what I might be doing wrong. Thanks in advance, -Steve

3 11

Meta State Machine PseudoExit transitions
by Johan Gielens 01 Jul '11

01 Jul '11

Hello, I'm trying to implement a PseudoExitState in my boost meta state machine. This is the situation: http://i55.tinypic.com/2a83yar.png. Currently, when going from Transport to either Situation A or B, it throws an "no_transition" in the SubState for the "convertible event" needed by the PseudoExit state. (This is event6 in the example described below) According to the documentation (http://www.boost.org/doc/libs/1_46_1/libs/msm/doc/HTML/ch03s02.html#d0e930) and the corresponding example, there should be some kind of transition triggered by "event6" from SubState2 to Substate1 (see http://www.boost.org/doc/libs/1_46_1/libs/msm/doc/HTML/examples/DirectEntry…, in the transition table for SubFsm2). I don't see an arrow in the state diagram between SubState2 and SubState1, nor can I figure out why I would want such a transition. In my SubState's transition table, I have defined the transition from Transport to PseudoExit1 and 2: g_row< Transport , Sensor , Exit1 , &SubFront::SDownstreamCheck >, g_row< Transport , Sensor , Exit2 , &SubFront::SDownstreamNoCheck > and in the TopState from PseudoExit1 and 2 to SituationA and B: _row< Sub::exit_pt< SubFront::Exit1 > , TransportDone , SituationA >, _row< Sub::exit_pt< SubFront::Exit2 > , TransportDone , SituationB >, So do i have to handle an "TransportDone" event in the SubState? And what are my Start and End states? I would appreciate your help :) Best Regards, Johan

2 7

Re: [Boost-users] Boost-users Digest, Vol 2769, Issue 5
by Tom Tan 01 Jul '11

01 Jul '11

------------------------------ > > Date: Thu, 30 Jun 2011 15:00:13 -0400 (EDT) > From: Jeremiah Willcock <jewillco(a)osl.iu.edu> > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] [Graph]questions regarding > boost::graph::adjacency_list constructor prototype > > On Thu, 30 Jun 2011, Tan, Tom (Shanghai) wrote: > > > > > While studying boost.graph, I stumbled upon this constructor definition: > > > > ????template <class EdgeIterator> > > > > ??? adjacency_list(EdgeIterator first, EdgeIterator last, > > > > ????????????????????????? vertices_size_type n, > > > > ????????????????????????? edges_size_type = 0, > > > > ????????????????????????? const GraphProperty& p = GraphProperty()) > > > > ????? : Base(n, first, last), m_property(new graph_property_type(p)) > > > > { } > > > > I have 2 questions here: > > > > -????????? What does ?edges_size_type = 0,? means here?? Assigning a value to a TYPE, instead of a parameter? Can > > anyone please point me to an explanation of this grammar usage? > > It's like if the code was "edges_size_type x = 0", but since the parameter > is not used, removing the name avoids compiler warnings. Nice to know this trick. Never knew that the 'x' can be omitted in this case. > > > > > -????????? Why the necessary of edges_size_type = 0 parameter,? since there?s a range pair of ?EdgeIterator first, > > EdgeIterator last?? > > It is not necessary, since the value of that parameter is never used. It > is probably there match the interface of some other constructor, either in > adjacency_list or some other graph class. I guessed so but it's better to confirmed. Thanks for the help. -Tom

1 0

[Range] Select forward or reverse traversal at compile time?
by Alastair Rankine 01 Jul '11

01 Jul '11

Given a bidirectional range R, is it possible to select at compile time whether we want to iterate forwards or backwards? Below is a test app. At the commented line, I would like to transparently construct a forward or reverse range, ie either [begin(range), end(range)] or [rbegin(range), rend(range)] respectively, depending on the definition of the Reversed template parameter. Just to be clear, the desired output is: forward: abc reversed: abc I can make this work by using a functor class with partial specialisation to construct the iterator_range, using begin/end or rbegin/rend respectively. But it's a bit ugly and it would seem like something that boost range would provide anyway? (Note that boost::reverse() is NOT what I am after.) #include <boost/assign/list_of.hpp> #include <boost/range/algorithm/copy.hpp> #include <boost/range.hpp> #include <vector> #include <iostream> template <typename Reversed, typename Range> std::string Print(const Range& range) { typedef boost::iterator_range< typename boost::mpl::eval_if< Reversed, boost::range_reverse_iterator<const Range>, boost::range_iterator<const Range> >::type> IterRange; // want to convert it to a forward range here IterRange forwardRange(range); std::string result; boost::copy(forwardRange, std::back_inserter(result)); return result; } int main(int argc, char* argv[]) { using boost::assign::list_of; std::vector<char> a = list_of('a')('b')('c'); std::vector<char> b = list_of('c')('b')('a'); std::cout << "forward: " << Print<boost::mpl::false_>(a) << std::endl << "reversed: " << Print<boost::mpl::true_>(b) << std::endl; return 0; }

3 5