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[boost.python] How to get derived class from base class in Python?
by Marcin Kalicinski 08 Jul '07

08 Jul '07

This may potentially be unrelated to Boost.Python, but how to do an equivalent of C++ dynamic_cast in Python, having all the classes wrapped using boost.python? See below: // All the components inherit from Component class Component { }; class ComponentA: public Component { }; class ComponentB: public Component { }; // Find a component by name Component *FindComponent(const char *name); // In C++ result of FindComponent may be dynamic_casted to appropriate type: void f() { Component *c = FindComponent("a"); ComponentA *a = dynamic_cast<ComponentA *>(c); } How to do this in Python (all Component classes are wrapped)? def f(): c = FindComponent("a") # Unforunately Python sees c as an instance of Component, not as ComponentA which it really is a = ??? Thanks, Marcin

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Re: [Boost-users] [Serialization] link errors serializing user types via pointer
by Sean Cavanaugh 08 Jul '07

08 Jul '07

Ok well in trying to get the serialization library working on my environment, I am having trouble loading user types via pointer. I've simplifed the class in question down to a struct containing PODs. Changing the trivial example to save and load via a local stack variable (i.e. ar & pass-by-reference) does work, however the real program I am trying to save a graph of structures foo with pointers to bar, I'm back to the original link error when trying to load the graph back, even when the root type passed into serialize is a reference type. My environment is WinXP w/ msvc8sp1 (aka visual studio 2005 sp1), and boost 1.34 pseudoprogram: #include <iostream> #include <fstream> #include "boost/serialization/access.hpp" #include "boost/archive/text_iarchive.hpp" #include "boost/archive/text_oarchive.hpp" struct MyVector3 { float X; float Y; float Z; MyVector3() {} MyVector3(float x, float y, float z) : X(x), Y(y), Z(z) {} }; template<class Archive> void serialize(Archive & ar, MyVector3& v, const unsigned int version) { ar & v.X; ar & v.Y; ar & v.Z; } int main(int argc, const char** argv) { // Saving via pointer works --- std::string filename("TestVector.raw"); MyVector3* WriteVector = new MyVector3(1.1f, 2.2f, 3.3f); std::ofstream ofs(filename.c_str()); boost::archive::text_oarchive oa(ofs); oa & WriteVector; ofs.close(); // Loading via pointer does not --- MyVector3* ReadVector = NULL; std::ifstream ifs(filename.c_str()); boost::archive::text_iarchive ia(ifs); ia & ReadVector; // <--- commenting this line out makes the link error go away, but then you can't load anything ifs.close(); } Link error is error LNK2019: unresolved external symbol "public: class boost::archive::detail::basic_pointer_iserializer const * __thiscall boost::archive::detail::basic_iarchive::load_pointer(void * &,class boost::archive::detail::basic_pointer_iserializer const *,class boost::archive::detail::basic_pointer_iserializer const * (__fastcall*)(class boost::serialization::extended_type_info const &))" (?load_pointer@ basic_iarchive@detail@archive@boost@@ QAEPBVbasic_pointer_iserializer@234@AAPAXPBV5234@P6IPBV5234@ ABVextended_type_info@serialization@4@@Z@Z) referenced in function "public: static void __fastcall boost::archive::detail::load_pointer_type<class boost::archive::text_iarchive,struct MyVector3 *>::invoke(class boost::archive::text_iarchive &,struct MyVector3 * &)" (?invoke@?$load_pointer_type@ Vtext_iarchive@archive@boost@@PAUMyVector3@@@ detail@archive@boost@@SIXAAVtext_iarchive@34@AAPAUMyVector3@@@Z) error LNK2019: unresolved external symbol "public: static class boost::archive::detail::basic_pointer_iserializer const * __fastcall boost::archive::detail::archive_pointer_iserializer<class boost::archive::text_iarchive>::find(class boost::serialization::extended_type_info const &)" (?find@?$archive_pointer_iserializer@ Vtext_iarchive@archive@boost@@@ detail@archive@boost@@SIPBVbasic_pointer_iserializer@234@ ABVextended_type_info@serialization@4@@Z) referenced in function "public: static void __fastcall boost::archive::detail::load_pointer_type<class boost::archive::text_iarchive,struct MyVector3 *>::invoke(class boost::archive::text_iarchive &,struct MyVector3 * &)" (?invoke@?$load_pointer_type@ Vtext_iarchive@archive@boost@@PAUMyVector3@@@ detail@archive@boost@@SIXAAVtext_iarchive@34@AAPAUMyVector3@@@Z) error LNK2019: unresolved external symbol "void const * __fastcall boost::serialization::void_upcast(class boost::serialization::extended_type_info const &,class boost::serialization::extended_type_info const &,void const * const,bool)" (?void_upcast@ serialization@boost@@YIPBXABVextended_type_info@12@0QBX_N@Z) referenced in function "void * __fastcall boost::serialization::void_upcast(class boost::serialization::extended_type_info const &,class boost::serialization::extended_type_info const &,void * const)" (?void_upcast@ serialization@boost@@YIPAXABVextended_type_info@12@0QAX@Z)

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Grabbing web page content
by Scott Meyers 07 Jul '07

07 Jul '07

I'm looking for an easy way to grab the contents of a web page, i.e., something like this (ignoring error handling): std::string pageContent = getPageContent("http://www.interestingsite.com/funkypage.html"); Is there a Boost library that will give me this kind of interface? I know I can build this on top of asio, but I'd prefer something where I don't have to do much more work than the above. If there's no Boost library, I'd welcome suggestions for other cross-platform ways to achieve this. Thanks, Scott

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Re: [Boost-users] Grabbing web page content
by Chad Walters 07 Jul '07

07 Jul '07

>> If there's no Boost library, I'd welcome >> suggestions for other cross-platform ways to achieve this. > > Most Un*x systems have libcurl, which will do this. > I don't know about Windows, but this looks promising > <http://sourceforge.net/projects/curl/> See http://curl.haxx.se/libcurl/ Lots of *nix flavors and Windows are supported. There is also a pointer to curlpp, which provides OO C++ bindings: rrette.com/textpattern/index.php?s=cURLpp Chad Walters

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[filesystem] building for cygwin
by frederic.bron＠alcan.com 07 Jul '07

07 Jul '07

In the documentation, it is written what follows for compiling with cygwin. Basically set BOOST_POSIX_API when building for cygwin and BOOST_WINDOWS_API when building for windows (i.e. -mno-cygwin). My question is: how to set BOOST_POSIX_API in user-config.jam? I have tried <define>BOOST_POSIX_API but it did not work. I have tried <cflags>-DBOOST_POSIX_API <cxxflags>-DBOOST_POSIX_API... and the -DBOOST_POSIX_API is given to g++ but I still have the windows behaviour. For example cout << boost::filesystem::path("/cygdrive/c/toto").file_string() ; gives \cygdrive\c\toto. Can you help to get the POSIX behaviour when compiling without "-mno-cygwin"? Regards, F. Bron The library's implementation code automatically detects the current platform, and compiles the POSIX or Windows implementation code accordingly. Automatic platform detection during object library compilation can be overridden by defining either BOOST_POSIX_API or BOOST_WINDOWS_API macros. With the exception of the Cygwin environment, there is usually no reason to define these macros, as the software development kits supplied with most compilers only support a single platform. The Cygwin package of tools supports traditional Windows usage, but also provides an emulation layer and other tools which can be used to make Windows act as Linux (and thus POSIX), and provide the Linux look-and-feel. GCC is usually the compiler of choice in this environment, as it can be installed via the Cygwin install process. Other compilers can also use the Cygwin emulation of POSIX, at least in theory. Those wishing to use the Cygwin POSIX emulation layer should define the BOOST_POSIX_API macro when compiling bother user programs and the Boost.Filesystem's object-library. Avis : Ce message et toute pièce jointe sont la propriété d'Alcan et sont destinés seulement aux personnes ou à l'entité à qui le message est adressé. Si vous avez reçu ce message par erreur, veuillez le détruire et en aviser l'expéditeur par courriel. Si vous n'êtes pas le destinataire du message, vous n'êtes pas autorisé à utiliser, à copier ou à divulguer le contenu du message ou ses pièces jointes en tout ou en partie. Notice: This message and any attachments are the property of Alcan and are intended solely for the named recipients or entity to whom this message is addressed. If you have received this message in error please inform the sender via e-mail and destroy the message. If you are not the intended recipient you are not allowed to use, copy or disclose the contents or attachments in whole or in part.

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[Boost.Graph] Property map of a bundled property
by Ewgenij Sokolovski 07 Jul '07

07 Jul '07

Hello, I want to apply dijkstra_shortest_paths to my Graph. I have added the lengths of the edges with while adding the edges with the function add_edge(vi, vj, distance, *nodesGraph) where vi, vj are the vertex descriptors, distance is the length of the edge and nodesGraph is a pointer to my graph. Now I need to provide an appropriate property map for the bundled property "distance". In the manual I read that I have to provide a member pointer to the property value: file:///usr/share/doc/packages/boost-doc/libs/graph/doc/bundles.html But in my case I do not have a class with members like 'Highway' in the manual. In my case the bundled property is represented by a single float value. And so I need access to it, not to some members of it. I tried to write weight_map(get(&float, myGraph)) instead of weight_map(get(&Highway::miles, map)) in the example, but then I get a compiler message "expected primary expression before "," token". So how can I access the distance? Or comes the compiler message due to some other bug in my code? Ewgenij -- Psssst! Schon vom neuen GMX MultiMessenger gehört? Der kanns mit allen: http://www.gmx.net/de/go/multimessenger

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[serialization] DLL woes
by Anders Wang Kristensen 07 Jul '07

07 Jul '07

Hi, I'm trying to serialize a class using two functions located in different DLLs. I can serialize fine by calling one function, but when I call the second it triggers an assertion in extended_type_info.cpp: // make sure that attempt at registration is done only once assert(lookup(eti) == m_self->m_map.end()); Apparently the class is registered twice, but how do I avoid that? -- Anders

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[1.34.0][serialization][iostreams] Memory leaks
by Ying 07 Jul '07

07 Jul '07

The attached code works fine with version 1.33.1 but generates memory leaks with 1.34.0. Not sure it's a bug in Serialization or Iostreams. Compiler: Visual Studio 2005 SP1 Thanks, Ying http://www.lw-works.com - Clipboard Recorder #include <cstdlib> //#include <boost/array.hpp> #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> //#include <boost/serialization/deque.hpp> #include <boost/iostreams/categories.hpp> #include <boost/iostreams/filter/zlib.hpp> #include <boost/iostreams/filtering_stream.hpp> #include <boost/iostreams/concepts.hpp> // sink, source #include <boost/iostreams/stream.hpp> #include <vector> #if _MSC_VER # ifdef _DEBUG # include <crtdbg.h> # ifndef new # define new new(_NORMAL_BLOCK, __FILE__, __LINE__) # endif # ifndef malloc # define malloc(size) _malloc_dbg(size, _NORMAL_BLOCK, __FILE__, __LINE__) # endif # endif #endif namespace cmn{ namespace iostreams{ template<typename Container> class container_sink { public: typedef typename Container::value_type char_type; typedef boost::iostreams::sink_tag category; container_sink(Container& container) : container_(container) { } std::streamsize write(const char_type* s, std::streamsize n) { container_.insert(container_.end(), s, s + n); return n; } Container& container() { return container_; } private: Container& container_; }; // class container_sink }} // namespace cmn::iostreams namespace cmn{ namespace iostreams{ template<typename Container> class container_source { public: typedef typename Container::value_type char_type; typedef boost::iostreams::source_tag category; container_source(Container& container) : container_(container), pos_(0) { } std::streamsize read(char_type* s, std::streamsize n) { using namespace std; streamsize amt = static_cast<streamsize>(container_.size() - pos_); streamsize result = (min)(n, amt); if (result != 0) { std::copy( container_.begin() + pos_, container_.begin() + pos_ + result, s ); pos_ += result; return result; } else { return -1; // EOF } } Container& container() { return container_; } private: typedef typename Container::size_type size_type; Container& container_; size_type pos_; }; // class container_source }} // namespace cmn::iostreams namespace cmn{ template<class T, class Container> bool compress_object(Container& v, const T& o) { typedef cmn::iostreams::container_sink<Container> sink; boost::iostreams::stream<sink> outs(v); boost::iostreams::filtering_stream<boost::iostreams::output> fs; fs.push(boost::iostreams::zlib_compressor()); fs.push(outs); boost::archive::text_oarchive oa(fs); oa << o; return true; } template<class T, class Container> bool decompress_object(const Container& v, T& o) { //ASSERT(v.size()); if(!v.size()) return false; typedef cmn::iostreams::container_source<const Container> source; boost::iostreams::stream<source> ins(v); boost::iostreams::filtering_stream<boost::iostreams::input> fs; fs.push(boost::iostreams::zlib_decompressor()); fs.push(ins); boost::archive::text_iarchive ia(fs); ia >> o; return true; } } // namespace cmn int main() { _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | /*_CRTDBG_CHECK_ALWAYS_DF | _CRTDBG_CHECK_CRT_DF | */_CRTDBG_LEAK_CHECK_DF); std::string data; std::vector<char> buf; cmn::compress_object(buf, data); cmn::decompress_object(buf, data); return 0; }

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[Graph] I could not get the reversed graph!
by jiangfan shi 06 Jul '07

06 Jul '07

HI, All, I could not get a instance of reversed graph by calling make_reverse_graph(g). That is, I have following type: typedef adjacency_list< listS, listS, bidirectionalS, property<vertex_index_t, std::size_t>, no_property> G; typedef reverse_graph<G, G&> ReverseG; //Maybe something wrong here. After I call make_revserse_graph(G) as following, I could not get a instance of modified graph by accessing some fields of ReverseG. ReverseG tmp=boost::make_reverse_graph(g); //I try to get the reservsed graph here. The only field is tmp.m_g, which is G& type and the original graph, but is not the reversed graph. Thanks. Jiangfan

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Boost is a finalist in the SourceForge.net Community Choice Awards
by David Abrahams 06 Jul '07

06 Jul '07

According to http://sourceforge.net/awards/cca we're nominated in this category: Best Technical Design: The project most likely to inspire awe with its technical perfection If you think Boost deserves this award, go to http://sourceforge.net/awards/cca and vote for us. I'm not sure what we'd win, but it's always nice to be recognized. Cheers! -- Dave Abrahams Boost Consulting http://www.boost-consulting.com The Astoria Seminar ==> http://www.astoriaseminar.com

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