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

[lexical_cast] Fast conversion from boost::iterator_range<std::string::iterator>?
by Michel Morin 13 Oct '11

13 Oct '11

lexical_cast made optimizations for some types (such as `std::string`) to achieve better performance. But, from my experience, it seems that lexical_cast does not make any optimization for `boost::iterator_range<std::string::iterator>`. Is there any plan to add optimization for such iterator ranges? Currently, - `lexical_cast<int>(std::string(iter_rng.begin(), iter_rng.end()))` is faster than `lexical_cast<int>(iter_rng)`. - Assuming it is safe to use `std::atoi`, `std::atoi(&iter_rng.front())` is faster than both of the above two methods. (`iter_rng` is an instance of `boost::iterator_range<std::string::iterator>`.) Regards, Michel

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[xpressive] treating special literals as non-regex
by Ovanes Markarian 13 Oct '11

13 Oct '11

Hello *, I ran into a problem, that I use some regex to split a string by some delimiters. My interface to the outer world is non-regex. A user can pass anything like delimiter. E.g. $d$ can be a valid delimiter. If I use sregex_token_iterator with regex created as: as_xpr("$d$") are $ treated as regex special characters and I have to escape them or can I safely use them in this context? If I have to escape the special characters is there any helper function like protect("$d$"). Many thanks for help, Ovanes

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help with boost::spirit:parsing out a list of menuitems
by Littlefield, Tyler 13 Oct '11

13 Oct '11

Hello: I have a client I'm writing, where the server sends data to the client to display as a menu in one instance. I wanted to use boost::spirit to parse this out. So, here's the code. I have three questions: 1) What can I do better/differently? 2) When I parse out my menuitem, if there's no flag, can it be set to 0 by default somehow? 3) Where is menuitem returned? Is there a way I can push it to a queue since I'll have more? My actual parser will look something like: pstart >> item >> *(delem >> item) >> pend; Here is the code I have currently: struct menuitem { std::string name; int flag; int choice; }; BOOST_FUSION_ADAPT_STRUCT( menuitem, (std::string, name) (int, flag) (int, choice)) namespace ascii = boost::spirit::ascii; namespace qi = boost::spirit::qi; //I'd like to just take a char* here, since that's my payload. copying the char* to a std::string will take extra time, is there a way to do that? BOOL Menu::Parse(const std::string &data, int length) { std::string::const_iterator it, itEnd; it = data.begin(); itEnd = data.end(); //we construct a few parsers to make things easier. qi::rule<std::string::const_iterator, char, ascii::space_type> pstart = qi::char_('['); qi::rule<std::string::const_iterator, char, ascii::space_type> pend = qi::char_(']'); qi::rule<std::string::const_iterator, char, ascii::space_type>delem = qi::char_('|'); qi::rule<std::string::const_iterator, menuitem(), ascii::space_type>item = qi::char_("a-zA-Z0-9 -.?!$@") >> qi::char_('(') >> -qi::int_ >> qi::char_(':') >> qi::int_ >> qi::char_(')'); if (!qi::phrase_parse(it, itEnd, pstart >> item >> pend, ascii::space)) { return false; } return true; } -- Take care, Ty Web: http://tds-solutions.net The Aspen project: a light-weight barebones mud engine http://code.google.com/p/aspenmud Sent from my toaster.

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Boost message_queue: when I receive an object, how can I remove it from the queue?
by pietro 13 Oct '11

13 Oct '11

I noticed that, when I get an object from a Boost message_queue with the *receive() member functions, that object remains in the queue. So if I read the same message_queue multiple times, I keep getting copies of the same objects, even if nothing has been inserted from the producer's side. Is there a way to remove an object from the queue once it has been read? In message_queue I found no member function that allows to do it. E.g.: (this is pseudo code; the consumer is shown and the producer would be in a separate process) boost::scoped_ptr<boost::interprocess::message_queue> pMQueue; message_queue::remove("myQueue"); pMQueue.reset(new message_queue(open_or_create, "myQueue", 100, sizeof(MyClass))); MyClass token; std::vector<MyClass> tokens; size_t recvdSize = 0; float timeDelay = 100; // milliseconds bool dataAvailable = true; // If I do this block twice, I receive the same tokens twice while(dataAvailable) { ptime t = microsec_clock::universal_time() + milliseconds(timeDelay); dataAvailable = pMQueue->timed_receive(&token, sizeof(token), recvdSize, 0, t); if(dataAvailable && recvdSize > 0) tokens.push_back(token); else ... } Note: in this example, MyClass' objects are fixed sized POD member variable objects only. -- View this message in context: http://boost.2283326.n4.nabble.com/Boost-message-queue-when-I-receive-an-ob… Sent from the Boost - Users mailing list archive at Nabble.com.

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[graph] vertex property Graph type cyclic definition problem. forward declaration not possible.
by Christoph 13 Oct '11

13 Oct '11

Hi, i would like to use the bundled properties feature of the boost graph library to specify the vertex properties of my graph. The problem is that i would like to have some graph type dependent descriptor type map defined within these vertex properties. Here is the example: // begin code #include <iostream> #include <boost/graph/adjacency_list.hpp> struct vertex_properties { vertex_properties () : color (-1) {} int color; std::list <int> free_colors; std::map<int,link_graph_traits::edge_descriptor> used_colors; // this is a cycle def problem }; struct edge_properties { edge_properties () : color (-1) {} int color; }; struct graph_properties { int delta; }; typedef boost::adjacency_list < boost::listS, boost::vecS, boost::bidirectionalS, vertex_properties,// this is a cycle problem edge_properties, graph_properties> link_graph; typedef boost::graph_traits <link_graph> link_graph_traits; int main(int argc, char** argv) { link_graph g; return 0; } // end code This example won't compile because the 'struct vertex_properties' contains a variable declaration of a std::map which contains the type ('link_graph_traits::edge_descriptor') as a template parameter that is not defined yet. I tried to forward declare the 'struct vertex_properties;' and move the definition of 'struct vertex_properties {...};' behind the graph type definition but then the compiler complained about. The forward declaration code, that does not compile, too follows: // begin code #include <iostream> #include <boost/graph/adjacency_list.hpp> struct vertex_properties; struct edge_properties { edge_properties () : color (-1) {} int color; }; struct graph_properties { int delta; }; typedef boost::adjacency_list < boost::listS, boost::vecS, boost::bidirectionalS, vertex_properties, edge_properties, graph_properties> link_graph; typedef boost::graph_traits <link_graph> link_graph_traits; struct vertex_properties { vertex_properties () : color (-1) {} int color; std::list <int> free_colors; std::map <int, link_graph_traits::edge_descriptor> used_colors; }; int main(int argc, char** argv) { link_graph g; return 0; } // end code I do not want to use (void*) and std::reinterpret_cast to work around this problem. I hope that you can help me with a technique not using casts. I assume that there may be a possibility to first declare the graph type without the vertex_properties struct and then 'adding' the vertex_propterties struct after defining the graph. best regards Christoph

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Quaternions and SLERP
by Yves Rogez 13 Oct '11

13 Oct '11

Hello, I'm currently searching for a BLAS and geometrical library in C++ for ray-tracing simulation. I would like to know if Boost provides an implementation of the SLERP (Spherical Linear Interpolation) with Quaternions. As far as I could read in the Boost::Quaternions docs, it is not integrated, maybe it is elsewhere in boost ? I also found QVM which is not integrated with boost but extensively uses it. Is that in your mind a reliable solution ? (I have to compute a huge set of quaternion interpolations and compositions during my simulation steps). Thanks in advance for your replies, Regards, Yves

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Boost asio deadline_timer, bug?
by Allan Nielsen 13 Oct '11

13 Oct '11

Hi Is this a bug, or am I doing something wrong? #include <iostream> #include <boost/asio.hpp> #include <boost/bind.hpp> using namespace std; using namespace boost::asio; struct A { A(io_service & service) : timer1(service), timer2(service) { timer1.expires_from_now( boost::posix_time::seconds(5) ); timer1.async_wait(boost::bind(&A::handler, this, _1)); timer2.expires_from_now( boost::posix_time::seconds(2) ); timer2.async_wait(boost::bind(&A::interrupt, this, _1)); } void handler(const boost::system::error_code &ec) { cout << "Forbidden handler" << endl; assert(0); } void handler_interrupted(const boost::system::error_code &ec) { cout << "Hello world" << endl; } void interrupt(const boost::system::error_code &ec) { cout << "Interrupted" << endl; int res = timer1.cancel(); assert(res > 0); timer1.expires_from_now( boost::posix_time::milliseconds(0) ); timer1.async_wait(boost::bind(&A::handler_interrupted, this, _1)); } int count, max, timeout1, timeout2; deadline_timer timer1; deadline_timer timer2; }; int main() { io_service service; A a(service); service.run(); return 0; }

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[Accumulators] Calling extractors on empty accumulator_set
by Dylan Klomparens 12 Oct '11

12 Oct '11

Hello all, I am curious, what mean is obtained from this code snippet? boost::accumulators::accumulator_set<int, boost::accumulators::features<boost::accumulators::tag::mean> > Accumulator; int Mean = boost::accumulators::mean(Accumulator); It appears to be non-zero when I test it. Is there some way I can tell that the average was taken for an empty data set? I was looking around in the documentation for the accumulator library, but was unable to find an answer to this question. Thanks in advance! -- Dylan

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using numpy instead of numeric
by Leila Baghdadi 12 Oct '11

12 Oct '11

Hello, I am very new to boost, I had a few files which build and run fine with boost , but return a numeric array, I now need to change my code to return a numpy array as I am sending it in another python package for further processing, I have been searching the web trying to find a simple example to do this conversion but so far was unsuccessful, The sample of my code is attached, any help is greatly appreciated! Leila

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boost::iterator_facade and assignment operation
by Arun Ramasamy 12 Oct '11

12 Oct '11

HI, I'm using the boost iterator_facade class to implement a random access iterator for my class. When I try to assign the iterators to one another, the compiler fails saying 'operator =' function is unavailable". Sample code from my implementation below: |class MyClass{ class Iterator : public boost::iterator_facade<Iterator, T, boost::bidirectional_traversal_tag>{ protected: void increment(); bool equal(const Iterator& rhs)const; //etc || //... Note - no method implemented to support assignment | | } }| I'd assumed that it'll be possible to assign iterators to each other. Why is the assignment operator not supported by iterator_facade. It implements other operations (like ++ and ==)by making the derived version implement private methods (like increment and equal). Am I missing something. The boost documentation doesn't mention why this is not supported. Thanks AR

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