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Iterator Adaptor Question
by Hickman, Greg 01 Nov '02

01 Nov '02

The following code illustrates a problem I'm having trying to use iterator_adaptor. Basically, I have a container of shared pointers to mutable, and I'd like to provide a const_iterator to clients that disallows modification of both the shared pointer as well as the pointee. Specifically, I'd like to prevent clients from writing the two lines preceeding the return from main below. Can anyone help? Thanks, Greg #include <boost/iterator_adaptors.hpp> #include <boost/shared_ptr.hpp> #include <vector> using namespace boost; using namespace std; struct Shape { virtual ~Shape() {} virtual void draw() const = 0; virtual void update() = 0; }; struct Concrete_shape : Shape { void draw() const {} void update() {} }; typedef shared_ptr<Shape> Shape_ptr; typedef shared_ptr<const Shape> Const_shape_ptr; struct Picture { typedef vector<Shape_ptr> Shapes; // Declare a const_iterator that converts // to the underlying Shape_ptr to a // Const_shape_ptr. Since the returned // Const_shape_ptr is a temporary, clients // shouldn't be allowed to modify it. typedef iterator_adaptor< Shapes::const_iterator, default_iterator_policies, value_type_is<Const_shape_ptr>, reference_is<const Const_shape_ptr>, iterator_category_is<input_iterator_tag> > const_iterator; const_iterator begin() const { return const_iterator(shapes_.begin()); } Shapes shapes_; }; int main(int argc, char* argv[]) { Picture pic; const Picture& cpic = pic; pic.shapes_.push_back(Shape_ptr(new Concrete_shape)); Picture::const_iterator i = cpic.begin(); // I'd like to prevent clients from writing... i->reset(new Concrete_shape); *i = Const_shape_ptr(new Concrete_shape); return 0; }

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Property Map deep copy
by Björn Lindberg 01 Nov '02

01 Nov '02

I have an external iterator_property_map to an adjacency_list, using std::vector to store std::string as values. I need to copy this map, but a deep copy so that all the strings are unique to the copy. Is there an easy way to do this? I thought about constructing a new property map from a copy of the underlying vector, but this presents two other questions: (i) will the vertex-to-string mappings of the old map still be valid in the constructed copy? (ii) is there a way to extract the underlying vector from the property map? I couldn't find information on this in the online documentation. Björn

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[BGL] How to prune a BFS or exit a BFS
by kweeheong 01 Nov '02

01 Nov '02

I have a custom BFS visitor used to traverse a graph. Is there a built-in way to - prune off a vertex's descendants from the search - exit a BFS These ( pruning and terminating ) are separate situations. I believe the following will work; however, I do not know how to access the relevant data structures. - To prune off a vertex's descendents from the search In the custom BFS visitor's discover_vertex event, set the color of all its adjacent descendants to "black". - To exit a BFS In the custom BFS visitor's discover_vertex event, once the required vertex is found, empty the queue of vertices. How can I access a vertex's color and a BFS's queue? Or is there a better way?

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How to pass result of boost::bind to arg of template function ?
by hugo duncan 31 Oct '02

31 Oct '02

Hi, I want to pass the result of a boost::bind as an argument of a templated function of a class, and am struggling to find a signature that will let me do this. Is this possible? if so what signature should the function have ? Any help much apreciated Hugo #include "boost/function/function1.hpp" #include "boost/bind.hpp" class another_class {}; class my_class { public: typedef another_class ObjectType; //! this works fine passing a boost::function object template <class ReturnType> void add(const boost::function1<ReturnType,ObjectType>& arg) { boost::function1<ReturnType,ObjectType> fn_obj=arg; } //! this should work when passed the result of a boost::bind template <class ReturnType> void add(?what goes here? & arg) { function1<ReturnType,ObjectType> fn_obj(arg); } }; int fn(another_class,int) { return 1; } int main(int, char**) { my_class c; c.add(boost::bind(&fn,_1,1)); }

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[bgl] breadth_first_search for shortest paths (fwd)
by Joel Young 31 Oct '02

31 Oct '02

Dear Jeremy, et al, I am trying to implement a shortest paths algorithm on a directed graph. As I have unit edge weights, I would rather use breadth_first_search rather than dijkstra. // Is this a good candidate for addition? template <class Map, class Tag> struct vertex_marker : public boost::base_visitor<vertex_marker<Map,Tag> > { typedef Tag event_filter; vertex_marker(Map p_map,int p_val) : m_map(p_map),m_val(p_val) { } template <class Vertex, class Graph> void operator()(Vertex v,const Graph&) { boost::put(m_map,v,m_val); } Map m_map; int m_val; }; template <class Map, class Tag> vertex_marker<Map,Tag> mark_vertices(Map p_map, Tag, int p_v) { return vertex_marker<Map,Tag>(p_map,p_v); } boost::breadth_first_search( mygraph, rootnode, boost::visitor(boost::make_bfs_visitor( std::make_pair( boost::record_distances( boost::get(boost::vertex_distance,mygraph), boost::on_tree_edge()) , std::make_pair( mark_vertices( boost::get(boost::vertex_distance,mygraph), boost::on_initialize_vertex(), std::numeric_limits<int>::max()) , mark_vertices( boost::get(boost::vertex_distance,mygraph), boost::on_start_vertex(), 0) ) ) )) ); The problem is that on_start_vertex does not seem to be implemented for breadth_first_search, but it is for depth_first. For dijkstra, the start node seems to be automaticly zeroed. I guess I could mod Am I missing something really obvious here or is there an inconsistency across the algorithms? Shouldn't on_start_vertex be used for all of the graph algorithms? Also, I can't seem to find documentation on neighbor_bfs.hpp Thanks, Joel

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Debug regex++ in VC6
by r_gharavi 31 Oct '02

31 Oct '02

When I build a stand-alone debug xll with regex++ (static linking), Excel refuses to accept it as an addin. It works fine in release mode. Due to reasons beyond my control :-), I am using VC6 STL. Any pointers would be appreciated. Thanks.

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d_heap bug
by Tsvetomir Valtchev 31 Oct '02

31 Oct '02

[I tried to contact the library's author, dietmar.kuehl@claas- solutions.de, but the message bounced back.] Dear Dietmar, I was looking for a better heap class than the one in STL and I was delighted to come across your d_heap class included in the Boost library. Unfortunately, I had a number of problems with it, and I figured you might be interested in some feedback. First, the class didn't compile with VC.NET (and probably won't with VC 6 either). This might be due to non-conformance on the part of Microsoft's compiler and some known limitations with template support, but for some of the issues I think they were due to the non- conformance of the code itself. Second, to my dismay, the code turned out to be seriously flawed. The following simple fragment, for example, causes a crash: THeap::pointer ptrs[10]; ptrs[0] = heap.push(12); ptrs[1] = heap.push(16); heap.remove(ptrs[0]); heap.remove(ptrs[1]); After some debugging and deciphering of the code, I found that the remove() function didn't handle a special case where the node to be 'sifted up' coincided with the last "hole" left in the tree. I think pop() had a similar problem. (In my fixed version, I have expressed pop() in terms of remove(), which resolves the problem and also avoids some code duplication.) I hope some day you get around to publishing an improved version. Another suggestion I have is some way to make sure that the pointer's passed back by client code are valid. Extensive use of assertions throughout the code might also prevent various programming errors. Regards, // Chango V.

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Regex++ and UTF-8
by Gitit 31 Oct '02

31 Oct '02

Hi, We want to use regex++ (version 3.31) with UTF-8 strings. I tried to match a UTF-8 character of 2 bytes to the regex "." and the match failed. It seems regex++ handles these 2 bytes as two separate characters. 1) Is there a "native" way in the regex++ library for using UTF-8 strings? Can we use UTF-8 strings to compare against a compiled regex (the regex is in ASCII only)? Can the regex itself hold UTF-8 characters? 2) Is converting to wchar_t our only option? As far as I understand, wchar_t does not cover the entire range of characters covered by UTF-8, so it may not be enough. Any other ideas? thanks, Gitit.

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Re: [Boost-Users] Re: regex: flag for "global" search?
by dick.bridges＠tais.com 30 Oct '02

30 Oct '02

The boost::regex_search example bumps the start to march through the sub-expressions and the boost::regex_grep examples demonstrate using the 'callback' for each term. I was kinda hoping the library provided a "convenience version" that would take something like "(\\w+)(?:\\.(\\w+))*" and populate the match_results as if the terms had been expanded <e.g.> "(\\w+)(?:\\.(\\w+))?(?:\\. (\\w+))?(?:\\.(\\w+))?"</e.g.> Perhaps to some arbitrary limit? Oh well, given the riches provided, a little while loop now and then is surely a small price to pay. ;) Thanks for the response. I'm continually amazed at the ethos fostered by Boost group members. "Edward Diener" <eddielee@tropic To: boost-users(a)yahoogroups.com soft.com> cc: Sent by: news Subject: [Boost-Users] Re: regex: flag for "global" search? <news(a)main.gmane .org> 10/29/2002 04:54 PM Please respond to Boost-Users Use boost::regex_grep. The boost::regex_search only finds the first match. <dick.bridges(a)tais.com> wrote in message news:OF6181960C.1A0F5C63-ON88256C61.006996C6@tais.net... > I'm trying to capture the sub-expressions in a fqdn (e.g., > one.two.three.com.) One piece of Perl-speak for the expression is: "/ > (\w+)\./g". I've been using boost_search and trying variations on "(?: > (\\w+)\\.)+" but I can't seem to get all the sub-expressions into the > match_results. > > There's got to be a flag I've been overlooking. Any suggestion will be > appreciated. Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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regex: flag for "global" search?
by dick.bridges＠tais.com 30 Oct '02

30 Oct '02

I'm trying to capture the sub-expressions in a fqdn (e.g., one.two.three.com.) One piece of Perl-speak for the expression is: "/ (\w+)\./g". I've been using boost_search and trying variations on "(?: (\\w+)\\.)+" but I can't seem to get all the sub-expressions into the match_results. There's got to be a flag I've been overlooking. Any suggestion will be appreciated. TIA

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