February 2010 - Boost-users

Strange iterator_traits of iterator_facade
by Swerts, Benjamin 26 Feb '10

26 Feb '10

Hello all, I have a class that is templated on an iterator type. As it only works with bidirectional and random access iterators, I thought I would impose that as follows: template<typename T> class A { A() { checkIterator(std::iterator_traits<T>::iterator_category()); }; template<typename Tag> void checkIterator( Tag ); void checkIterator( std::bidirectional_iterator_tag ) {}; void checkIterator( std::random_access_iterator_tag ) {}; void checkIterator( boost::random_access_traversal_tag ) {}; }; This works when T is a standard iterator but not when it's one of my iterator_facade subclasses. For example: class const_iterator : public iterator_facade<const_iterator, const B, boost::random_access_traversal_tag, B> When using this class with A<const_iterator> I get a linker error because the checkIterator function is called with: boost::detail::iterator_category_with_traversal<struct std::input_iterator_tag,struct boost::random_access_traversal_tag> I certainly cannot add a specialization of checkIterator with this tag to class A. Could anyone shed some light on this problem? I'm working with Boost 1.39.0 on MSVC2008SP1. Thanks a lot in advance! Greets, Ben

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[boost-users][filesystem] some missing function
by Sascha Ochsenknecht 26 Feb '10

26 Feb '10

Hi, in Boost.Filesystem I can find a function: template <class Path> std::time_t last_write_time(const Path& p); which is corresponding to st_mtime (last modification time) of the stat structure. Within the stat structure, their are also st_atime and st_ctime defined, but there are no corresponding functions. Is there a special reason for that? Maybe not portabel? Couldn't they be added? E.g. template <class Path> std::time_t last_access_time(const Path& p); template <class Path> std::time_t last_status_change_time(const Path& p); Cheers, Sascha

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understanding Xcode and Boost
by David Rangel 26 Feb '10

26 Feb '10

Hello, Thanks to Igor R for helping me get started with the compilation problems of the regex test program at http://www.boost.org/doc/libs/1_35_0/more/getting_started/unix-variants.htm… Xcode. I renamed all id occurrences to idd in the regex headers, but still get errors. Also, I don't understand why this is necessary for Xcode but not using the command line compilation suggested in the getting started guide. Is Xcode generally more problematic when using libraries like Boost or GSL? Is there a better recommended development environment than Xcode, or is it simple once the error is tracked down? Thanks again for any input. Message: 7 Date: Wed, 24 Feb 2010 23:52:22 +0200 From: Igor R <boost.lists(a)gmail.com> To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] Xcode and Boost Message-ID: <cfe0a3cf1002241352v15440e32wc44f9885861e2efc(a)mail.gmail.com > Content-Type: text/plain; charset=UTF-8 > I am interested in using Xcode on OSX to develop some code, and have been > having some troubles compiling the regex example given at: > http://www.boost.org/doc/libs/1_35_0/more/getting_started/unix-variants.html > I can compile using the command line, but not in Xcode. Rename all the occurrences of local variables named "id" in the relevant regex headers.

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Re: [Boost-users] result_of protocol
by Hicham Mouline 26 Feb '10

26 Feb '10

>---------------------------------------------------------------------------------- >struct extract_rule { > > template <typename Sig> struct result; > > template <typename Holder> >struct result< extract_rule(const Holder) > { > typedef const typename Holder::type& type; > }; > template <typename Holder> > typename result< extract_rule(const Holder) >::type > operator()( const Holder& h ) const > { > return h.rule; > } >}; >---------------------------------------------------------------------------------- >1> with >1> [ >1> Sig=extract_rule (const onevariantrule<parameters_t,0,boost::spirit::istream_iterator> ) >1> ] >The template onevariantrule<> is defined _before_ extract_rule. >------------------------------------------------------------------------------------------- >template <typename parameters_t, unsigned n, typename Iterator> >struct onevariantrule { > typedef .... type; >}; >------------------------------------------------------------------------------------------- >Holder matches onevariantrule<parameters_t,0,boost::spirit::istream_iterator>. >That template instantiation is indeed a class. Both specializations template <typename Holder> struct result< extract_rule(const Holder) > { }; and template <typename Holder> struct result< extract_rule(const Holder& ) > { ///// the reference was missing here, doh! typedef const typename Holder::type& type; }; were needed. Sorry for the spam,

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Boost.ASIO "deasynchronisation"
by Igore Dmit. 26 Feb '10

26 Feb '10

Hello, I'm developing networking library that provides RTMP-like networking using Boost.ASIO library. My problem is that any synchronous-access function breaks into many little functions that do some part of job and invoke async operation with "next" function as a handler, it makes the code really ugly and obfuscating. E.g. void hadshake that reads N bytes from peer, responds with those bytes + same count of other bytes, reads N bytes back and checks that they are the same. It breaks into: void start_handshake_wait(); void handle_handshake_wait(const boost::system::error_code&, std::size_t, buffer_ptr &); void handle_handshake_wait_write_dup(..same as above..); void handle_handshake_wait_write_mine(...); void handle_handshake_wait_read_mine_check(...); Every function uses boost::bind, so for some quite simple operation a lot of code is produced. Receiving a chunk of data breaks into: void read_header_head(); // header size depends on first byte void parse_header_head(); void parse_header_body(); void parse_chunk_body(); The only idea I came to is to use some tricks like coroutines. (Sorry for big listings) template<class T> class Context : public boost::enable_shared_from_this< Context<T> > { public: typedef boost::shared_ptr<Context<T> > ptr; private: typedef boost::shared_ptr<T> objptr_t; typedef void (T::*funcptr_t) (const BSYSECode&, std::size_t, Context<T>::ptr, buffer_ptr); objptr_t objptr_; funcptr_t funcptr_; public: std::map< std::string, buffer_ptr > buffers; int state; Context(objptr_t op, funcptr_t fp) : objptr_(op), funcptr_(fp), buffers(), state(0) { } template<typename AsyncReadStream> void async_read(AsyncReadStream &s, buffer_ptr buf) { boost::asio::async_read(s, *buf, boost::bind(funcptr_, objptr_, BASIOPErr, BASIOPBytes, this->shared_from_this(), buf)); } template<typename AsyncWriteStream> void async_write(AsyncWriteStream &s, buffer_ptr buf) { boost::asio::async_write(s, *buf, boost::bind(funcptr_, objptr_, BASIOPErr, BASIOPBytes, this->shared_from_this(), buf)); } }; #define CTX_PROLOG(c) \ if(!c) \ return; \ \ if(c->state == 0) { \ #define CTX_READ(c, s, b) \ c->state=__LINE__; \ c->async_read(s, b); \ return; \ } else if(c->state == __LINE__) { \ #define CTX_WRITE(c, s, b) \ c->state=__LINE__; \ c->async_write(s, b); \ return; \ } else if(c->state == __LINE__) { \ #define CTX_EPILOG \ } buffer_ptr is actually a shared_ptr to buffer, it's used to get buffer back to pool as it goes out of scope. With all this handshake becomes something more readable (to me, but it still cryptic; again, sorry for posting that much): class Handshaker : public boost::enable_shared_from_this<Handshaker> { private: Connection::ptr conn_; public: typedef boost::shared_ptr<Handshaker> ptr; typedef Context<Handshaker> context; Handshaker(Connection::ptr conn) : conn_(conn) { } void shake() { context::ptr ctx(new context(shared_from_this(), &Handshaker::perform)); perform(BSYSECode(), 0, ctx, buffer_ptr()); } private: void perform(const BSYSECode& err, std::size_t sz, context::ptr ctx, buffer_ptr buf) { if(err) return; CTX_PROLOG(ctx); CTX_READ(ctx, conn_->socket(), conn_->pool()->allocate(HandshakeSize)); CTX_WRITE(ctx, conn_->socket(), buf); ctx->buffers["mybuf"] = conn_->pool()->allocate(HandshakeSize); CTX_WRITE(ctx, conn_->socket(), ctx->buffers["mybuf"]); CTX_READ(ctx, conn_->socket(), conn_->pool()->allocate(HandshakeSize)); buffer_ptr mybuf = ctx->buffers["mybuf"]; buffer_ptr hisbuf = buf; if(boost::asio::buffer_size(*mybuf) != boost::asio::buffer_size(*hisbuf)) return; if(memcmp( boost::asio::buffer_cast<void*>(*mybuf), boost::asio::buffer_cast<void*>(*hisbuf), boost::asio::buffer_size(*mybuf) )) return; CTX_EPILOG; } }; Finally, the question: is there any library that provides functionality like that? I'd like to stick with it cause it looks like my implementation is really bad, HUGE bunch of limitations on code written that way, cryptic look, usage of macro, any local variable has to resort in ctx to survive async call.

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Re: [Boost-users] result_of protocol
by Hicham Mouline 26 Feb '10

26 Feb '10

-----Original Message----- >From: "Hicham Mouline" [hicham(a)mouline.org] >Date: 26/02/2010 09:40 AM >To: boost-users(a)lists.boost.org >Subject: Re: result_of protocol. >---------------------------------------------------------------------------------- >struct extract_rule { > > template <typename Sig> struct result; > > template <typename Holder> >struct result< extract_rule(const Holder) > { > typedef const typename Holder::type& type; > }; > template <typename Holder> > typename result< extract_rule(const Holder) >::type > operator()( const Holder& h ) const > { > return h.rule; > } >}; >---------------------------------------------------------------------------------- >1> with >1> [ >1> Sig=extract_rule (const onevariantrule<parameters_t,0,boost::spirit::istream_iterator> ) >1> ] >The template onevariantrule<> is defined _before_ extract_rule. >------------------------------------------------------------------------------------------- >template <typename parameters_t, unsigned n, typename Iterator> >struct onevariantrule { > typedef .... type; >}; >------------------------------------------------------------------------------------------- >Holder matches onevariantrule<parameters_t,0,boost::spirit::istream_iterator>. >That template instantiation is indeed a class. In the snippet above, I replaced Holder by what the compiler tells me it is in the error log, as ------------------------------------------------------------ struct extract_rule { template <typename Sig> struct result; template <typename Holder> struct result< extract_rule(const Holder) > { typedef const onevariantrule<parameters_t,0,boost::spirit::istream_iterator>::type& type; }; ------------------------------------------------------------ And this works. If msvc is able to see that Holder is that particular template instantiation in the error log, isn't it able to know then that Holder is a class? regards,

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[graph] parallel named graph and redistribute
by Andreas Zilian 26 Feb '10

26 Feb '10

Hello boost.graph users, I would like to use the PBGL with named vertices and later redistribute the graph. Unfortunately, I cannot compile the attached code, which - following the documentation - should work, since redistribute() just needs a property_map containing the new rank id's. A minimal example is shown below and a more verbose in the attachment. The example on redistribution in the tests of course works, but uses no named vertices. Are there any users of the parallel BGL who managed to solve this issue? And how? Moreover, could the new (serial) labeled_graph be an option? Thank you very much, Andreas #include <boost/graph/use_mpi.hpp> #include <boost/graph/distributed/adjacency_list.hpp> #include <boost/graph/distributed/mpi_process_group.hpp> using namespace boost; using boost::graph::distributed::mpi_process_group; //----------------------------------------------------------------------------- struct Topo { friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int version) { ar & user_id & rank_id ; } Topo( int uid=0, int rid=-1 ) : user_id(uid), rank_id(rid) {} int user_id; int rank_id; friend std::ostream& operator<< (std::ostream& o, const Topo& t) { o << "uid = " << t.user_id << ", rid = " << t.rank_id; return o; } }; //----------------------------------------------------------------------------- // named vertices in a graph namespace boost { namespace graph { template<> struct internal_vertex_name< Topo > { typedef multi_index::member< Topo, int, &Topo::user_id > type; }; template<> struct internal_vertex_constructor< Topo > { typedef vertex_from_name< Topo > type; }; }} typedef adjacency_list< vecS, distributedS< mpi_process_group, vecS >, directedS, Topo > Graph; int main(int argc, char* argv[]) { boost::mpi::environment env(argc,argv); Graph g; property_map< Graph, int Topo::*>::type rid_map = get(&Topo::rank_id, g); g.redistribute( rid_map ); return 0; }

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result_of protocol
by Hicham Mouline 26 Feb '10

26 Feb '10

Hello, I get the following msvc2008 error: error C2825: 'Holder': must be a class or namespace when followed by '::' in the following code ---------------------------------------------------------------------------------- struct extract_rule { template <typename Sig> struct result; template <typename Holder> struct result< extract_rule(const Holder) > { typedef const typename Holder::type& type; }; template <typename Holder> typename result< extract_rule(const Holder) >::type operator()( const Holder& h ) const { return h.rule; } }; ---------------------------------------------------------------------------------- 1> with 1> [ 1> Sig=extract_rule (const onevariantrule<parameters_t,0,boost::spirit::istream_iterator> ) 1> ] The template onevariantrule<> is defined _before_ extract_rule. ------------------------------------------------------------------------------------------- template <typename parameters_t, unsigned n, typename Iterator> struct onevariantrule { typedef .... type; }; ------------------------------------------------------------------------------------------- Holder matches onevariantrule<parameters_t,0,boost::spirit::istream_iterator>. That template instantiation is indeed a class. It has the inner field called "type". Any ideas would be appreciated,

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for help, some error of boost regx
by pirate-king 26 Feb '10

26 Feb '10

Hello everyone, When I use boost_1_41_0 of regx in vs2005, I met this runtime error: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::regex_error> > I search a lot, but there is not valid method to solve it. Can you do me a favor to give me the way to solve it. Thanks a lot my code is #include <boost/regex.hpp> #include <iostream> boost::regex e("(\\d{3, 4})[- ]?(\\d{4)})[- ]?(\\d{4})[- ]?(\\d{4})"); void print_captures(const std::string& regx, const std::string& text) { boost::regex e(regx); boost::smatch what; std::cout << "Expression: \"" << regx << "\"\n"; std::cout << "Text: \"" << text << "\"\n"; if (boost::regex_match(text, what, e, boost::match_extra)) { unsigned i, j; std::cout << "** Match found **\n Sub-Expressions: \n"; for (i = 0; i < what.size(); ++i) std::cout << " $" << i << " = \"" << what[i] << "\"\n"; std::cout << " Captures:\n"; for (i = 0; i < what.size(); ++i) { std::cout << " $" << i << " = {"; for (j = 0; j < what.captures(i).size(); ++j) { if (j) std::cout << ", "; else std::cout << " "; std::cout << "\"" << what.captures(i)[j] << "\""; } std::cout << "}\n"; } } else { std::cout << "** No match found **\n"; } } int main(int , char* []) { print_captures("(([[:lower:]]+)|([[:upper:]]+))+", "aBBcccDDDDeeeeeee"); return 0; }

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io_service run thread exits on network disconnect (chat server example)
by A.Agrawal＠patrick.com.au 26 Feb '10

26 Feb '10

Hello, My code is similar to the one in chat_server example in boost documentation. In my program I use boost asio to communicate with server. Client has following code to connect to the server: Class Members: class DJClient { tcp::socket *_socket; boost::asio::io_service io_service; boost::thread *t; ............................MORE........................................... } void DJClient::Connect() //To Connect to the server { tcp::resolver resolver(io_service); tcp::resolver::query query("10.21.7.5", "50000"); tcp::resolver::iterator endpoint_iterator = resolver.resolve(query); _socket = new tcp::socket(io_service); tcp::endpoint endpoint = *endpoint_iterator; _socket->async_connect(endpoint, boost::bind(&DJClient::handle_connect, this, boost::asio::placeholders::error, ++endpoint_iterator)); t = new boost::thread(boost::bind(&boost::asio::io_service::run, &io_service)); return; } //Callback function after connection has been attempted, also reads data asynchronously from the server void DJClient::handle_connect(const boost::system::error_code& error, tcp::resolver::iterator endpoint_iterator) { if (!error) { boost::asio::async_read(*_socket, boost::asio::buffer(_inbound_data_length), boost::bind(&DJClient::handle_read_data_length, this, boost::asio::placeholders::error)); } else if (endpoint_iterator != tcp::resolver::iterator()) { _socket->close(); tcp::endpoint endpoint = *endpoint_iterator; _socket->async_connect(endpoint, boost::bind(&DJClient::handle_connect, this, boost::asio::placeholders::error, ++endpoint_iterator)); } } Client writes to the server using the following code, this happens in the main thread (the one that called Connect), asynchronously void DJClient::GetAllWIs(const char* oow_id) { io_service.post(boost::bind(&DJClient::write_wis_for_oow_req, this, oow_id)); } void DJClient::write_wis_for_oow_req(const char* oow_id) { boost::asio::async_write(*_socket, oow_id, boost::bind(&DJClient::handle_write, this, boost::asio::placeholders::error)); } Everything works fine without any problem until network cable is unplugged. After network cable is unplugged, a call to GetAllWI does not call write_wis_for_oow_req. I can see an exit thread message in Visual Studio output window. I suspect that io_service::run exits and io_service is no longer valid and that is why it does not call the method. My program needs to handle this scenario and Client should be able to detect network problem and reconnect. 1. It would be great help if someone can suggest a way to handle this scenario. Is there a way to know this io_service::run has exited. 2. I can see in watch window that io_service._impl.stopped changes its value from 0 to 1. But I do not know how to access it programmatically. Any response will be greatly appreciated as I am not very experience in using boost. Thanks in advance Anil Agrawal Patrick Technology & Systems

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