July 2007 - Boost-users - lists.preview.boost.org

[serialization] minor comment error
by Sean Cavanaugh 09 Jul '07

09 Jul '07

In basic_binary_oarchive.hpp there exists a comment which is obviously the result of an uncorrected cut-and-paste (it looks like the comment just needs to be deleted) ///////////////////////////////////////////////////////////////////////// // class basic_text_iarchive - read serialized objects from a input text stream template<class Archive> class basic_binary_oarchive : public detail::common_oarchive<Archive>

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Re: [Boost-users] [serialization] hacking serialization : handles to pointers
by Sean Cavanaugh 08 Jul '07

08 Jul '07

On 7/8/07, Robert Ramey <ramey(a)rrsd.com> wrote: > > Sean Cavanaugh wrote: > > Ok I've spent a good chunk of my day making a set of custom archive > > class, based on the portable_binary_iarchive and > > portable_binary_oarchive. > > > > > > I have a non-virtual class hierarchy named Asset, in memory this is a > > cyclic graph, but my requirements are that this structure cannot be > > serialized all at once, it has to be broken up at boundaries. So > > the archiver serializes the first Asset* (which is always the root > > object passed into operator&). This object serializes as normally as > > per the boost serialization code, except except that when subsequent > > Asset*'s are encountered > > > > ?which point to a previously serialized object? or any subsequent > > Asset *? > > > > I send the pointer into an AssetManager class and translate the > > Asset* into a ResourceID, and serialize the ResourceID instead of the > > object. This is done by directly calling operator& inside > > save_override. > > > ******* > Hmmm this sounds to me exactly equivalent to what the serialization > system does by default for tracked objects. Objects serialized > through pointers are tracked by default. Your "ResourceID" seems a > re-implemenation of the "object id" used by the serialization libary > to track This is true, but the serialization libraries view of the id's only have archive scope, which means the same id's are used for totally different things when you use multiple archives. My ResourceID's have to be globally unique, in the sense they are GUIDs or relative pathnames, which can then be mapped to a fully qualified pathname and can be loaded on demand. As far as the archive class is concerned its a user defined translation (proxy-to-real and real-to-proxy) that exists for certain types. So in this case its conceptually an archive of archives. With the outermost archive being the filesystem, and the innermost being a single object (a file). The file only contains one object, and all links to other objects are handles (a filename). So the innermost code when it is loading from the filesystem, it knows that it wants a pointer to another object, but it only has its name. So it has to ask the filesystem class to translate the name into an object, which it can do because it can lookup if its already loaded and return that, or literally open another file based archive and read it in on demand, and return that. The archive class doesn't care about the specifics really, it just needs the means to achieve the result. So the archive's base class code should be doing this in a conceptual way: for_each type X, if has_user_defined_translation<X*> implement : on_save -> translate type X* to type ProxyX via a function : ProxyX RealToProxy(X* x), serialize the ProxyX on_load -> read ProxyX translate to X*, via a function : X* ProxyToReal(ProxyX& px), return the X* Except that this on_save and on_load example needs to have yet another template argument, on whether the first occurence of X should be literally saved or not, since we might be saving a hierarchy of Bar's that always save handles to Foo's at all times. > > > ... > > > > I also have to hard-code the full list of derived Asset types and > > manually provide specializations for all of them in save_override and > > load_override. > > > **** > Well, since they're different - I would expect each of them to have a > different serialize function. If all the serialize functions are the > same, it would seem that something should be moved from the derived > class to the base class. > > > > If I use the base class, I end up slicing my class down to its base, > > and cannot serialize it. > > > **** > serializing through a base class pointer solves this problem as well. In my currently kind-of-working hacked up version of the archive classes the methods load_override are nearly identical when specializing for AssetModel, AssetTexture, etc. The behavior is constant (proxy-to-real translation or vice-versa) but the type is not. I can slice them here safely on saving, but not on loading (since the C++ code in the serialize method 'ar & foo', is expecting a more-derived type to be filled in). > I can't make serialize virtual, since the intrusive serialize methods > > are templates, but it certainly would solve the problem if it were > > possible. > > *** > I suspect that if the other changes suggested were implemented this > would disappear as a problem. I don't think I've tried it, but > rather than including boiler plate code in each derived class, one > might try adding a "mix-in" base class which contains the serialize > function. I'll play around with alternatives, I basically spent the day learning the archive templates by watching the code flow. > > > In addition the bodies of all of my overrides are completely > > identical except for the classname (AssetModel, AssetTexture, etc). > > > > Which means I'll be wrapping the bodies of a generic save_override > > and load_override in a macro, and have to manually add all Asset > > derived classes to a list of classes inside my archive class. Which > > means that my archiver cannot be generic, even though I have managed > > to make it a template in the sense that the passed in asset manager > > and base asset types are template parameters. > > > *** > looks to me that you've gotten off on the wrong foot and stuck with it. That isn't possible with learning new code :) This is what the path of least resistance yielded, with the docs and examples provided by boost. Basically this is as far as I got without having to directly hack on the existing boost code, and having to deal with a crash course on the code flow and internal data structure of everything. > > > *** me this is exactly the wrong approach. Now you've coupled your > classes > to be serialized to a specific archive. This means you won't be able to > use > any other archive type and you've defeated one of the main benefits to the > serialization library. Perhaps it wasn't a suitable library for your > task. The library can do what I want, because I have the source code :) Anyway the classes aren't coupled to the archive with what I've come up with so far, its the other way around. I definitely do not want my classes to understand archiving beyond a very basic sense of having to call operator& on most of their fields, since I plan on having several wildly different archive classes calling the serialize methods on my classes. So I have a working implementation, how do I make it better? > > **** > Maybe you might try doing it in the simplest way. > > I can't see how what you want to do is different than what everyone else > uses the library for. And I can't see how what you want to do is > different > than what the examples do. > > I could get the behavior I want by altering the serialize methods, but then it would be ill formed for other archives. I could also template specialize the serialize methods for the archive in question, but then I would have to write more than one. Its the archives job to interpret what to do when you call ar & foo. I anticipate having more data than I can load, so I need to load and save at an object level. But I still need to write the serialize methods as if they all could fit in memory, since I plan on having other archive classes that do operate on the graph of what is loaded at runtime (i.e. to compute garbage collection). In essence the archive classes need to be made to be programmable for these behaviors to work: Graph of Foo: Saving: save the first Foo*, translate all further Foo*'s into a user defined handle with a user defined function and save that instead. Loading: load the first Foo*, assume all further Foo*'s are saved with a user defined handle, translate them back into live objects on demand, and also use the existing caching scheme to prevent having to translate the same user-defined handle over and over. Graph of Bar: Saving: save all Bar's, but save all occurences of Foo*'s as handles Loading: save all Bar's, but load all occurences of Foo*'s from handles Garbage Collecting Foo: 'Saving' : archive an array of live root level Foo objects, build a list of all Foo* that are reachable through serialization. Compare this list to the full list of Foo objects, and unload the ones that are missing.

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How to use boost iostream with zlib
by Meryl Silverburgh 08 Jul '07

08 Jul '07

Hi, Can you please tell me how can I use boost iostream with zlib to inflate an byte stream? Where can I find an example? Thank you.

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non-boost: project idea help. Java expert apperciated.
by chun ping wang 08 Jul '07

08 Jul '07

Dear boost community. Right now I am planning on doing somewhat of a mock boost for java. http://cs.calstatela.edu/wiki/index.php/Current_MS_Students/Chun_ping_Wang. I am not going to use the name boost but i want to know a.) a good name for it. b.) five common non-ui files you think Java needs that it is missing. All implementation can be done using low level arrays and iterators (if needed). Thanks

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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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