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passing variable into template parameters.
by chun ping wang 02 May '06

02 May '06

Its more of a c++ question but i wonder how would I pass constant variables into template parameters such as nth_index_iterator. Example: void func(const int& var) { nth_index_iterator<var>::type; } Is this possible whats the work around this limitation?

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Re: [Boost-users] [smart_ptr] Resetting an intrusive_ptr
by Nat Goodspeed 02 May '06

02 May '06

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org [mailto:boost-users- > bounces(a)lists.boost.org] On Behalf Of Scott Meyers > Sent: Tuesday, May 02, 2006 1:00 PM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] [smart_ptr] Resetting an intrusive_ptr > > Peter Dimov wrote: > > The reason for p = 0 working in intrusive_ptr's case is that > intrusive_ptr > > has an assignment operator taking a raw pointer. The other smart pointer > > types do not. > > I understand that, my question was more about why this operation is > supported only for intrusive_ptr. [Nat] The library discourages casual conversion from Foo* to shared_ptr<Foo> because it is a Bad Thing when you instantiate a second shared_ptr<Foo> for the same Foo* value. Now you have two different reference counts floating around on the heap. When either goes to zero, every shared_ptr<Foo> value based on the other reference count becomes a land mine. On the other hand, intrusive_ptr is designed to be able to cope with casual conversion of exactly that type. That's why, unlike shared_ptr, the intrusive_ptr constructor that accepts a dumb pointer is not marked 'explicit'. Simple dumb-pointer assignment works for the same reason. Concerning the missing reset() method, I can only surmise that the author considered it unnecessary, given assignment support. I for one wouldn't object to it being added.

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[smart_ptr] Resetting an intrusive_ptr
by Scott Meyers 02 May '06

02 May '06

Suppose I have an auto_ptr, shared_ptr, or scoped_ptr. If I want to set it to null, I do this (assuming the pointer is named p): p.reset(); // okay If I try this, p = 0; // error I get an error during compilation. In other words, reset works, but assignment of the null pointer does not. But suppose p is an intrusive_ptr. Now p.reset(); // error fails, and p = 0; // okay succeeds. In other words, assignment works, but reset does not. I find this, er, unintuitive. Does anybody know why intrusive_ptr marches to its own nullifying drummer? Thanks, Scott

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WG: defining a function<>-object with a return value of the same type (recursive declaration)
by Oliver.Kowalke＠qimonda.com 02 May '06

02 May '06

Hello, how can I define a function<> object which returns a value of the same type: // doesn't work with gcc-4.1 class X; typedef function< X() > X; X x1 = bind(...); X x2 = x1(); Regards, Oliver

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Re: [Boost-users] passing variable into template parameters.
by Nat Goodspeed 02 May '06

02 May '06

From: boost-users-bounces(a)lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of chun ping wang Sent: Tuesday, May 02, 2006 12:54 AM To: boost-users(a)lists.boost.org Subject: [Boost-users] passing variable into template parameters. Its more of a c++ question but i wonder how would I pass constant variables into template parameters such as nth_index_iterator. Example: void func(const int& var) { nth_index_iterator<var>::type; } Is this possible whats the work around this limitation? [Nat] Could you just make func() a template function, and have 'var' be a template parameter rather than a runtime function parameter?

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incremental_components, component_index for listS, listS adjacency_list
by Sean Kelly 02 May '06

02 May '06

Hi All, I couldn't figure out how to use the component_index facility of the incremental components algorithm when operating on an listS, listS adjecency_list so I rolled my own as per below. Any suggestion on how to use the provided interface are appreciated. thanks Sean using namespace boost; typedef graph_traits<BlockDependencyGraph>::vertices_size_type size_type; typedef BlockDependencyGraph::vertex_descriptor vertex_descriptor; typedef BlockDependencyGraph::vertex_iterator vertex_iterator; BlockDependencyGraph& graph = _blk_dep_view->get_graph(); // Disjoint sets requires Rank to map vertex_descriptors onto integers typedef std::map<vertex_descriptor, int> rank_storage_t; rank_storage_t rank_map; typedef associative_property_map<rank_storage_t> rank_t; // Disjoint sets requires Parent to map vertex_descriptors onto vertex_descriptors typedef std::map<vertex_descriptor, vertex_descriptor> parent_storage_t; parent_storage_t parent_map; typedef associative_property_map<parent_storage_t> parent_t; disjoint_sets<rank_t, parent_t> component_set(make_assoc_property_map(rank_map), make_assoc_property_map(parent_map)); initialize_incremental_components(graph, component_set); incremental_components(graph, component_set); // Not at all clear how to extract components using component_index interface // when graph is listS, listS adjacency_list... so we roll our own. // // Index vertices by representative component in a multimap typedef std::map<vertex_descriptor, std::vector<vertex_descriptor> > components_t; components_t components; vertex_iterator curr(0), end(0); for(tie(curr, end) = vertices(graph); curr != end; ++curr) { components[component_set.find_set(*curr)].push_back(*curr); } // Print all components size_t n_c(0); for(components_t::const_iterator c = components.begin(); c != components.end(); ++c, ++n_c) { std::cout << "component " << n_c << std::endl; for(std::vector<vertex_descriptor>::const_iterator element = c->second.begin(); element != c->second.end(); ++element) { std::cout << graph[*element]->get_name() << std::endl; } }

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Fusion. transform_view example
by John Christopher 02 May '06

02 May '06

Hello, The example at the bottom of: http://spirit.sourceforge.net/dl_more/fusion_v2/libs/fusion/doc/html/fusion… does not compile; I am using MinGw 3.4.2. #include <iostream> #include <boost/fusion/sequence.hpp> #include <boost/fusion/algorithm.hpp> using namespace boost::fusion; struct square { template <typename T> struct result { typedef int type; }; template <typename T> int operator()(T x) const { return x * x; } }; typedef vector<int, short, double> vector_type; int main (int argc, char ** argv) { vector_type vec(2, 5, 3.3); transform_view<vector_type, square> transform(vec, square()); std::cout << transform << std::endl; // return 0; } More specifically it is the line std::cout << transform << std::endl; that seems to create the problem. I was also wondering why operator() of square return int and not T. Thanks

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Re: [Boost-users] Timer
by Andy Little 02 May '06

02 May '06

"Vivek Bhat" <bhat.vivek(a)gmail.com> wrote > Hello, I'm a Mechanical Engineer (see: programming-knowledge defficient) and > I need some code to output an elapsed time, accurate to within at least > hundredths of a second. Hi Vivek. Actually I think you are on the wrong boost list. The one you want for this sort of query is the boost user list gmane.comp.lib.boost.user. I have cross posted this item there and you should send any followups there only too. > It appears to me as though the 'timer' > library<http://www.boost.org/libs/timer/timer.htm>is ideal for this > application, but when I try to run the simple code given > in the documentation, I get errors regarding missing .hpp files. I'm > assuming that I have made errors in downloading and installing the boost > libraries. I tried to read the 'getting started' section, but I'm having > difficulty understanding. Are there any more simple 'getting started' > instructions available for programming dunces running Windows? As far as I know Boost.Timer is just a wrapper for the C standard timer functions in <ctime>. Anyway it would be helpful to provide more details of the compiler you are using and the actual error messages you are getting too. Hope this helps regards Andy Little

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[program_options] Abort trap by store
by Pascal Vizeli 02 May '06

02 May '06

Hi, I habe a problem with store(parse_config_file(...), ...); I don't know why... That isn't my first program with program_options but it is my first program with parse_command_line and parse_config_file in one. Here is my code. First I parse the command line, second I parse the config file. Is it a very simple script. With my debuger (gdb and ddd) I can see, that the problem is here: bpo::store(bpo::parse_config_file(conf_file, desc_file), vm); (at the "end" from script). vm is global definiert. The Namspace bpo ist boost::program_options I use the gcc 3.3.5 and I compile static with: /usr/local/lib/libboost_program_options-gcc-1_33_1.a My OS is OpenBSD What I make false? My script is at the end. Sorry for my bad english. I thanks for Help, Dear, Pascal Vizeli [cpp] bpo::variables_map vm_cmd; bpo::options_description desc_file("config file"), desc_cmd("command line"); // Make options descriptions desc_cmd.add_options() ("config,c", bpo::value<std::string>(), "The Config file") ("help,h", "produce help message") ; desc_file.add_options() ("port", bpo::value<int>()->default_value(6667), "IRC Server Port") ("server", bpo::value<char *>(), "IRC Server IP") ("nick", bpo::value<std::string>(), "Bot Nick") ("user", bpo::value<std::string>(), "username hostname servername :realname") ("nickserv", bpo::value<std::string>(), "Nickserv Identify string") ("oper-pw", bpo::value<std::string>(), "Oper Password") ("mode", bpo::value<std::string>(), "Mode for Bot") ("logchan", bpo::value<std::string>(), "A #Chan for logs") ("logchan_status", bpo::value<int>(), "Logchan On or Off") ("invite-chan", bpo::value<int>(), "Invite for logchan?") ("invite-command", bpo::value<std::string>(), "Invite Command") ("re-chan", bpo::value<int>(), "Refresh Channellist until SEC") ("logfile", bpo::value<std::string>(), "File for logs") ("chroot", bpo::value<char *>(), "Set the chroot dir (path)") ; // Parse CMD bpo::store(bpo::parse_command_line(argc, argv, desc_cmd), vm_cmd); bpo::notify(vm_cmd); if(vm_cmd.count("help")){ std::cout << desc_cmd << std::endl; std::cout << desc_file << std::endl; exit(0); } if(!vm_cmd.count("config")){ printo_err("Config file not found! Use --help for Infos"); exit(0); } // Open Config file std::ifstream conf_file(vm_cmd["config"].as<std::string>().c_str()); if(conf_file.is_open()){ // Parse Config file bpo::store(bpo::parse_config_file(conf_file, desc_file), vm); // Here is the false say my debuger bpo::notify(vm); }else{ printo_err("can't open the conf file!"); exit(0); } [/cpp]

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[BGL] parallel edges
by John Krajewski 02 May '06

02 May '06

How do I make a graph that will just ignore when I attempt to add a parallel edge? Is there a way to set this on the graph, or is it only determined by the type of storage structures I'm using with the graph? I want to use a vecS to store the edges, but I dont want to allow parallel edges. -John

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