July 2010 - Boost-users - lists.boost.org

Re: [Boost-users] Annoying compiler warnings in asio/error.hpp
by Hite, Christopher 16 Jul '10

16 Jul '10

> What you describe here is the opposite of what is stated in the lib. > As far as I understand the author's intention by declaring a global variable > static: introdcution of an own copy of this var in each compilation unit. The author just wanted a constant which you ask for a name/message. Actually the variable ssl_category is not used anywhere. They call get_ssl_category() which has a static function variable. That is another good trick to create a global variable which exists in all compilation scopes. Code like this in a header will generate on instance of X shared between compilation scopes. Class X{} inline X& getOneAndOnlyX(){ static X x; return x; } Anyways I'm guessing you could just kick ssl_category. I can't find these constants documented anywhere in the reference. ssl_category isn't used in tests. Some of the others are used, but since they are the same as what the inline functions would return. Perhaps the author was afraid in a multi threaded environment functions like getOneAndOnlyX() aren't safe. I know gcc by default generates atomic ops so only one X is constructed. Perhaps the idea was to ensure all these things were created before main() gets a chance to start threads. I don't have a checkout. Maybe someone could svn blame the file and find out who defined these things and ask them what they were thinking. Chris

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[Serialization] Why not allowing reset_object_address on object serialized throw a pointer ?
by Alain KOCELNIAK 16 Jul '10

16 Jul '10

This issue has already been discussed but was never addressed : http://lists.boost.org/boost-users/2008/11/42417.php https://svn.boost.org/trac/boost/ticket/4044 I don't understand why objects loaded as pointer can't be relocated : - These objects are stored in basic_iarchive_impl::object_id_vector as the others, so, technically speaking, we can change their "address" - There is situations where it is mandatory : for example when data, sharing some objects, are serialized / dispatched in separate archives => without relocating service at loading, sharing of object is not possible. For the moment, I workaround the limitation with a hack in the method basic_iarchive_impl::reset_object_address : I remove the "safeguard" which checks that the method is applied on a tracked object and immediately after the concerned object is read : ================================================ for(i = moveable_objects_recent; i < moveable_objects_end; ++i){ if(old_address == object_id_vector[i].address) break; } for(; i < moveable_objects_end; ++i){ ================================================ is replaced by ================================================= for(i = 0; i < object_id_vector.size(); ++i){ ================================================= I think that the limit can be properly removed by handling in "basic_iarchive_impl::load_pointer" the "moveable_objects_..." variables as it is done in "basic_iarchive_impl::load_object" As objects created by the serialization system are marked with "loaded_as_pointer" = true (this data is used by basic_iarchive_impl::delete_created_pointers) I think this data should be set to false by "reset_object_address". Is there other implication ? Alain.

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returning pointer to Boost::assign::map_list_of
by alapex0310＠gmail.com 16 Jul '10

16 Jul '10

Hi, I am new to Boost::Assign. I have a std::map<std::string, unsigned char> and I have a SomeClass with constructor SomeClass(std::string, std::map<std::string, unsigned char>*) and I want to pass the pointer to the result of map_list_of to SomeClass like this: SomeClass *psc = new SomeClass("SomeClassName",map_list_of("one",1)("two",2)("three",3)("four",4)("five",5); In the example at http://www.boost.org/doc/libs/1_43_0/libs/assign/doc/index.html#intro , the map_list_of is definitely returning a small map. I don't want to pass the map object itself but the pointer to the map object returned by map_list_of. Please help me. -Best regards

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[asio] creating acceptor on the stack causes seg-fault
by Steve Lorimer 16 Jul '10

16 Jul '10

Hi folks, I have the following class: using namespace boost::asio; // basic tcp server class server { boost::thread thread; ip::tcp::acceptor acceptor; io_service io_svc; // tcp_srv_conn object which will become the local end-point of the next incoming connection tcp_srv_conn_p new_conn; void loop(unsigned short port); void on_accept(const boost::system::error_code &err); public: server(); virtual ~server(); void serve(unsigned short port); void serve(const std::string &svc); void close(); }; and the constructor for server looks like this: server::server() : acceptor(io_svc), new_conn(new tcp_srv_conn(io_svc)) { } If I create a server object on the stack: server s; I get a segmentation fault deep inside the asio internals (something to do with a mutex), originating from initialising acceptor with my io_service object: acceptor(io_svc) Here is a stack trace of the core file: Marked in red is (#6) my server constructor and (#7) the basic_socket_acceptor constructor Core was generated by `tcp_srv.debug -p 12'. Program terminated with signal 11, Segmentation fault. #0 0x00007f8de6c3ed21 in pthread_mutex_lock () from /lib64/libpthread.so.0 (gdb) backtrace #0 0x00007f8de6c3ed21 in pthread_mutex_lock () from /lib64/libpthread.so.0 #1 0x0000000000421153 in boost::asio::detail::posix_mutex::lock (this=0x8) at /usr/include/boost/asio/detail/posix_mutex.hpp:71 #2 0x0000000000422db7 in scoped_lock (this=0x7f8de58d7a70, m=...) at /usr/include/boost/asio/detail/scoped_lock.hpp:36 #3 0x0000000000426e22 in boost::asio::detail::service_registry::use_service<boost::asio::socket_acceptor_service<boost::asio::ip::tcp> > (this=0x0) at /usr/include/boost/asio/detail/service_registry.hpp:94 #4 0x000000000042573a in boost::asio::use_service<boost::asio::socket_acceptor_service<boost::asio::ip::tcp> > (ios=...) at /usr/include/boost/asio/impl/io_service.ipp:195 #5 0x000000000042427d in basic_io_object (this=0x7f8de58d7bd0, io_service=...) at /usr/include/boost/asio/basic_io_object.hpp:72 #6 0x0000000000422fd7 in basic_socket_acceptor (this=0x7f8de58d7bd0, io_service=...) at /usr/include/boost/asio/basic_socket_acceptor.hpp:77 #7 0x000000000041fe63 in server (this=0x7f8de58d7b90) at src/tcp_srv.cpp:9 #8 0x000000000040d4d2 in app::start_here (this=0x7fffaab13b2f, ac=3, av=0x7fffaab13cd8) at test/server_test.cpp:65 Am I doing something stupid? How should I be creating my io_service and acceptor objects? TIA Steve

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boost::serialization trouble
by Sebastian Weber 16 Jul '10

16 Jul '10

Hi! I am experiencing quite odd errors with the serialization library: My program compiles fine, but crashes when static constants are declared, i.e. before the program even starts with main(). The debugger tells me that some singleton declared in the seralization library conflicts: Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000000 0x0000000100003aaf in H5::DataType::DataType () at singleton.hpp:149 149 BOOST_DLLEXPORT T & singleton<T>::instance = singleton<T>::get_instance(); Any suggestions would be great here. What makes it even harder to understand is the fact that the exact same code runs perferctly on a Linux machine, whereas the crash is on MacOS 10.6. My setup here is a boost 1.43.0 compiled with gcc 4.5 from pacports (or apples gcc 4.2, no difference). It seems that the singleton does things which are not allowed on a 10.6 MacOS machine... Many thanks for help, Sebastian Weber

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boost lambda wiht bind to stringstream::str
by Conoscenza Silente 16 Jul '10

16 Jul '10

Hi all I am trying to get familiar with boost lambda. Below I am using std::transform algorithm but when I try to call std::stringstream::str() function using lambda::bind I receive the following error message: TestBoost15Jul.cpp:49: error: no matching function for call to ‘bind(<unresolved overloaded function type>, const boost::reference_wrapper<std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> > >)’ Do you also know if is the right way to return the string that must be stored in the second vector used by std::transform? Regards AFG // C++ #include <iostream> #include <algorithm> #include <vector> #include <sstream> #include <string> // boost #include <boost/assign.hpp> #include <boost/assign/list_of.hpp> #include <boost/assign/std/vector.hpp> #include <boost/lambda/core.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> #include <boost/function.hpp> int main( int argc, char** argv ){ namespace bl = boost::lambda; using namespace boost::assign; std::vector< std::string > vIn = list_of("a")("b")("c")("d"); std::vector< std::string > vOut; std::stringstream outFmt; int nCount = 2; bl::var_type< int >::type _nCount( bl::var(nCount) ); bl::var_type< std::stringstream >::type _outFmt( bl::var(outFmt) ); std::transform( vIn.begin(), vIn.end(), vOut.begin(), ( _outFmt << bl::_1 << "=%" << _nCount << "%", _nCount++, bl::bind( &std::stringstream::str , boost::ref(outFmt) )() // this call to bind has some problem ) ); std::cout << outFmt.str() << std::endl; return 1; }

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Default weight map doesn't work for weighted grid graph in A-star search
by W.P. McNeill 16 Jul '10

16 Jul '10

I am trying to write a simple example of an a-star search over a 2-dimensional grid using the Boost Graph Library. The source is hosted here: http://github.com/wpm/Boost-Searchable-Grid-Example. My intent is for this to be a resource for other people writing a-star searches. I am seeing an error about a missing weight map when I try to compile the call to astar_search(). As far as I can tell, everything is in order. I hoping someone has insight into what I'm missing. My graph class is a rank-2 grid graph called weighted_grid defined like so: typedef grid_graph<2> weighted_grid; I have a simple map that returns a weight of zero for every edge. struct edge_weight_map { typedef float value_type; typedef float reference; typedef edge_descriptor key_type; typedef readable_property_map_tag category; reference operator[](key_type e) const { // All edges have a weight of zero. return 0; } }; I associate this map with the weighted_grid class by specializing property_map. template<> struct property_map<weighted_grid, edge_weight_t> { typedef edge_weight_map type; typedef edge_weight_map const_type; }; I've defined valid expression functions for this property map along with a Euclidean distance heuristic and a visitor that throws an exception when a goal vertex is reached. The complete source is viewable at the URL given above. With these definitions I can do concept checks on the ReadablePropertyMap, ReadablePropertyGraph, VertexListGraph, and AStarHeuristic concepts. I can instantiate a weighted_grid. I can get the edge weight map using get(edge_weight, g) and the vertex index map using get(vertex_index, g). I think I have written everything I need to do a-star search. However, the following call does not build: vertex_descriptor source = vertex(0, g), goal = vertex(3, g); astar_search(g, source, euclidean_heuristic(goal), visitor(astar_goal_visitor(goal)) ); I get a long error spew. The first relevant problem appears to be here: ... /opt/local/include/boost/graph/astar_search.hpp:350: instantiated from ‘void boost::detail::astar_dispatch1(VertexListGraph&, typename boost::graph_traits<G>::vertex_descriptor, AStarHeuristic, CostMap, DistanceMap, WeightMap, IndexMap, ColorMap, const Params&) [with VertexListGraph = boost::grid_graph<2ul, size_t, size_t>, AStarHeuristic = boost::euclidean_heuristic, CostMap = boost::detail::error_property_not_found, DistanceMap = boost::detail::error_property_not_found, WeightMap = boost::edge_weight_map, IndexMap = boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t>, ColorMap = boost::detail::error_property_not_found, Params = boost::bgl_named_params<boost::astar_goal_visitor, boost::graph_visitor_t, boost::no_property>]’ /opt/local/include/boost/graph/astar_search.hpp:372: instantiated from ‘void boost::astar_search(VertexListGraph&, typename boost::graph_traits<G>::vertex_descriptor, AStarHeuristic, const boost::bgl_named_params<P, T, R>&) [with VertexListGraph = boost::weighted_grid, AStarHeuristic = boost::euclidean_heuristic, P = boost::astar_goal_visitor, T = boost::graph_visitor_t, R = boost::no_property]’ main.cpp:36: instantiated from here ... (Line 36 main.cpp is the last line of the astar_search call.) This error message seems to be telling me that the weight map property for edges is missing, but I think I have properly implemented the get(edge_weight, g) function the documentation says is used to create the default weight map. Any idea what I'm doing wrong? Thanks.

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serialization using archive
by Long P 16 Jul '10

16 Jul '10

Hi I have come across the example for serialization in http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/example/serializat… In the following method async_write, the data typename T is put into an archive before being sent out. I would need to do the same thing here but the archive should be binary stream because I need to send this data to a third party application which expects a binary stream. Does anyone know how to do it? Thanks & Regards Long /// Asynchronously write a data structure to the socket. template <typename T, typename Handler> void async_write(const T& t, Handler handler) { // Serialize the data first so we know how large it is. std::ostringstream archive_stream; boost::archive::text_oarchive archive(archive_stream); archive << t; outbound_data_ = archive_stream.str(); // Format the header. std::ostringstream header_stream; header_stream << std::setw(header_length) << std::hex << outbound_data_.size(); if (!header_stream || header_stream.str().size() != header_length) { // Something went wrong, inform the caller. boost::system::error_code error(boost::asio::error::invalid_argument); socket_.io_service().post(boost::bind(handler, error)); return; } outbound_header_ = header_stream.str(); // Write the serialized data to the socket. We use "gather-write" to send // both the header and the data in a single write operation. std::vector<boost::asio::const_buffer> buffers; buffers.push_back(boost::asio::buffer(outbound_header_)); buffers.push_back(boost::asio::buffer(outbound_data_)); boost::asio::async_write(socket_, buffers, handler); } _________________________________________________________________

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postpone thread execution
by Lloyd 15 Jul '10

15 Jul '10

Hi, In boost::thread, when a thread is created, it starts execution at that instance itself. Instead of this, is it possible to postpone the execution? Thanks, Lloyd ______________________________________ Scanned and protected by Email scanner

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boost::lexical_cast<> with hex strings?
by anony 15 Jul '10

15 Jul '10

I'd like to do something like: boost::uint16_t b(std::lexical_cast<boost::uint16_t>("xa")); I have no control of the string stream that lexical_cast uses internally, so how could I implement this? P.S.: There are a lot of false statements made about this functionality on the web, some people claim that boost::lexical_cast<> can do the conversion out of the box, but this is not so in my tests.

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