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Re: [Boost-users] MPL. Nested Lambdas
by dilas dilas 22 Feb '10

22 Feb '10

Steven Watanabe wrote: >dilas dilas wrote: >> Please, tell me if one can write nested lambda expressions like >> >> " >> template<class Result, class Seq, class Elem> struct pairs: bm::fold<Seq, >>Result, bm::push_back<_1,bm::pair<Elem, _2 > > >{}; >> template<class Seq1, class Seq2> >> struct AllPairs: bm::fold<Seq1, bm::vector<>, pairs<_1,Seq2,_2> >{}; >> " >> >> without using intermediate metafunctions. >This ought to work, since the placeholders in AllPairs will be expanded >before >pairs is ever invoked. Here I've presented the example of "intermediate metafunction" i.e pairs. And I'm speaking about writing just one metafunction using nested construction. Is it possible? Yours respectfully, Dilas

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Re: [Boost-users] [fusion] runtime unsigned to a template argument compile-time unsigned
by Hicham Mouline 22 Feb '10

22 Feb '10

-----Original Message----- From: "Larry Evans" [cppljevans(a)suddenlink.net] Date: 22/02/2010 07:23 PM To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] [fusion] runtime unsigned to a template argument compile-time unsigned On 02/22/10 10:02, Larry Evans wrote: > On 02/21/10 05:27, Hicham Mouline wrote: > [snip] >>> >> 3. Can I generate an array of function pointers to the various >> at<>() functions and call the right one at runtime? > > The 2 attached files show how this can be done. > > Obviously, instead of: > > typedef > void(* > method_type > )(void) > ; > > you'd have: > > typedef > double(* > method_type > )(void) > ; > This could even be done for heterogeneous return types; however, in that case, a tagged variant. The tag for this variant would be the field index. In the attached code, this would be something like the super_numerals. ------------------------ This looks like it should go, already is in some library? I have many places where I read the index, and I would like to use the index as the template argument, thanks very much, will do,

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[fusion] runtime unsigned to a template argument compile-time unsigned
by Hicham Mouline 22 Feb '10

22 Feb '10

Hi, I have a struct adapted as a fusion sequence. My user inputs at runtime the index of the member she is interested in. Assuming all members are convertible to double, the only solution I found so far is: double f(unsigned index) { switch(index) { case 0: return boost::fusion::at_c<0>( sequence ); case 1: return boost::fusion::at_c<1>( sequence ); . case 6: return boost::fusion::at_c<6>( sequence ); } } To generate this: 1. 0 to fusion::result_of::size<Seq>::type::value - 1 is the range I want. 2. I can't use PP to generate the cases inside the switch 3. Can I generate an array of function pointers to the various at<>() functions and call the right one at runtime? I am basically looking for the runtime version of at_c. Regards,

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Accessing an element of multi_index_container using iterator_to
by Andrew Kokkalis 22 Feb '10

22 Feb '10

First of all, i'm a programmer with no much experience using Boost Libraries. I'm using Boost for academic purposes and here's my problem. I simply want to access an element of a multi_index_container, by using the iterator_to iterator. the container has entries that are <word(string), word_id(int), tf_idf(float)> and is indexed by unique order for the first two values :word and word_id. *Declaration of my container is below:* *struct counterpart { string word; int id; float tf_idf; counterpart(string word_, int id_) { word = word_; id = id_; tf_idf = 0.0; } }; struct word_name{}; //or word char struct word_id{}; struct word_tf_idf{}; typedef multi_index_container< counterpart, indexed_by< ordered_unique< tag<word_name>, BOOST_MULTI_INDEX_MEMBER(counterpart, string, word)>, ordered_unique< tag<word_id>, BOOST_MULTI_INDEX_MEMBER(counterpart, int, id)>, ordered_non_unique< tag<word_tf_idf>, BOOST_MULTI_INDEX_MEMBER(counterpart, float, tf_idf)> > > word_index;* word_index word_set; int word_count_id = 1; >From main, I insert some "entries" like below. *This a test main* *int main(void){ //insert to word_set pair<word_index::iterator, bool> word_pair; if((word_pair = word_set.insert(counterpart("apple", word_count_id))).second) //word does not exist word_count_id++; }* I want to access the entry inserted, as i could do with a map. ex map["apple"] The reason i do this, is because i want to get the value of a unique word_id, by accessing the name of the word and a unique word name by accessing a word_id. This of course is not possible, so i have to use iterator_to. But i cannot think how to do this. Should i prepeare a pair as donne when inserting? Also how a value or an entire entry is returned? In which form? Thank you all and I hope you can help me! Andrew Kokkalis undergraduate student of Informatics and Telecomunications University of Athens, Greece

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Re: [Boost-users] Foreach For iterating two containers
by Pete Bartlett 21 Feb '10

21 Feb '10

Gokulakannan Somasundaram wrote: >Meanwhile, a gentleman helped me by providing this code. Posting it here for any comments >#include <boost/typeof/typeof.hpp> > >#define FOREACH_2(def1, def2, r1, r2) \ > > for(std::pair<BOOST_TYPEOF((r1).begin()), \ > BOOST_TYPEOF((r2).begin())> _it12_((r1).begin(),(r2).begin()),\ > > _e12_((r1).end(), (r2).end()); \ [...] If you don't mind the "weight" of BOOST_TYPEOF just for a for loop, it's not bad as some of the complexity is hidden in that inner macro. However bear in mind in falls short of the original FOREACH because it uses its arguments r1 and r2 repeatedly which may be inefficient, or even flat out wrong, if r1 and/or r2 are temporaries. Also, there is an open ticket against some extra functionality in Boost.Foreach - BOOST_FOREACH_FIELD I think it is called. If that macro came to pass, I think you could solve your use case with a make_zip_range. Pete

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[graph] linking error read_graphviz
by Tillmann Vogt 21 Feb '10

21 Feb '10

Hello, My aim is to parse the graphviz-dot format with boost. The two examples from the getting-started web page build fine (in Ubuntu 9.10 and also Windows 7) Building graph-thingie.cpp in VC9.0 with boost 1.42 gives this error: example.obj : error LNK2001: unresolved external symbol "bool __cdecl boost::detail::graph::read_graphviz(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class boost::detail::graph::mutate_graph *)" (?read_graphviz@graph@detail@boost@@YA_NABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@PAVmutate_graph@123@@Z) 1>C:\Users\till\Documents\Visual Studio 2008\Projects\example\Release\example.exe : fatal error LNK1120: 1 unresolved externals The next thing I tried was building the "boost_graph" library separately by executing bjam in libs/graph/build which generated C:\Program Files (x86)\boost\boost_1_42\bin.v2\libs\graph\build\msvc-9.0\debug\libboost_graph-vc90-mt-1_42.lib and also a .lib in the release folder. The two new libs seem to be same as in boost/lib/ because they have the same size. So the question is: Do I really have to build "boost_graph" library separately to use the GraphViz readers, like it says on http://www.boost.org/doc/libs/1_42_0/libs/graph/doc/read_graphviz.html? I tried several compiler options and have all 8 variations of libboost_graph-vc90 ... .lib in /boost/lib, but no idea how the compiler magically choses the right one. I don't know what to try next, since I get similar errors on Ubuntu 9.10 (on Ubuntu boost 1.38 is preinstalled).

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Foreach For iterating two containers
by Gokulakannan Somasundaram 21 Feb '10

21 Feb '10

Hi, Is it possible to use Boost Foreach to iterate over two containers simultaneously? I have done my preliminary search in the lists and i couldn't find a solution. I am asking for a solution to iteration like this std::vector<int>::iterator iter1; std::vector<std::string>::iterator iter2; for( iter1 = cont1->begin(), iter2 = cont2->begin(); iter1 != cont1->end() || iter2 != cont2->end(); ++iter1, ++iter2 ) { int x = *iter1; std::string y = *iter2; ..... } If this is not present, please consider this as a feature request. The syntax below can also be considered forboth( int x, std::string y, cont1, cont2 ) { } Thanks, Gokul.

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[Filesystem V3] Filesystem Version 3 beta 1 available for download and comment
by Beman Dawes 21 Feb '10

21 Feb '10

The first beta release of Boost.Filesystem Version 3 is now available. The documentation can be viewed at http://mysite.verizon.net/beman/v3/index.htm Important differences from the prior version: http://mysite.verizon.net/beman/v3/v3.html The beta can be downloaded from the Boost vault. See http://www.boostpro.com/vault/index.php?&direction=0&order=&directory=Files… Installing the beta is described at http://mysite.verizon.net/beman/v3/install_distro.html I'm concerned about breaking existing code. While some workarounds have been provided already, I'd open to further suggestions as to how to mitigate code breakage. The tentative plan for integrating V3 into the boost release cycle involves several steps: * For the first boost release cycle, ship V2 as the default, but V3 is present and can be activated by users. * For an additional boost release cycle, ship V3 as the default, but V2 is present (but deprecated) and can be activated by users. * For the following boost release cycle, V2 is removed and no longer supported. The plan is to go through as many beta cycles as needed to reach stability. Although quite a bit of testing has already been done, this is definitely beta software that isn't ready yet for production use. Any comments appreciated. --Beman

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FW: [serialization] Polymorphic serialization with polymorphic archives problem...
by Bogdan 21 Feb '10

21 Feb '10

Hi Damien, Thank you for your quick reply. I believe I followed the rules: 1. polymorphic_derived1 and polymorphic_derived2 do include the serialization of the base class via "ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(polymorphic_base); " 2. there is no usage of BOOST_CLASS_EXPORT ( and there shouldn't be any: according to the documentation, in a dll setup one must declare BOOST_CLASS_EXPORT_KEY in the headers containing the classes to be serialized and BOOST_CLASS_EXPORT_IMPLEMENT in the .cpp files). In my example, there are exactly three declarations of BOOST_CLASS_EXPORT_KEY: one in polymorphic_base.hpp, and two in polymorphic_derived2.hpp one for polymorphic_derived1 and another for polymorphic_derived2. Similarly, there are only three usages of BOOST_CLASS_EXPORT_IMPLEMENT. 3. for deeper hierarchies where every class can be potentially serialized, one should probably register all the classes and not just the most derived children. I have the feeling that the type of deployment (dll vs exe) is the crux of the problem. For that, I created four different scenarios with the same source files and I got the following results: 1. all files in one exe with the serialization library linked statically - WORKS AS EXPECTED. 2. all files in one exe with the serialization library linked as a dll - WORKS AS EXPECTED. 3. serialization files in a separate dll. Both the main executable and my dll link with the dll version of the serialization library: main.exe my_serialization.dll boost_serialization.dll my_serialization.dll boost_serialization.dll Builds OK but FAILS at runtime , at run time I get a C++ exception BEFORE main() in basic_serializer_map.cpp around the line 48: 'archive_exception::multiple_code_instantiation with the message "code instantiated in more than one module - polymorphic_base"' 4. serialization files in a separate dll. Both the main executable and my dll link with the static version of the serialization library: main.exe my_serialization.dll boost_serialization.lib my_serialization.dll boost_serialization.lib Builds OK but FAILS at runtime while trying to serialize with the following exception thrown in oserializer.hpp(line 424):struct polymorphic::save(): 'unregistered void cast class polymorphic_derived1<-polymorphic_base in function 'int __cdecl main(int,char *[])'' The source code in the scenarios above is identical with the exception of dllexport/dllimport declaration needed for dlls. Whenever the serialization code is relegated to a different library it seems there are problems with boost serialization: - if boost is linked as a static lib into a user dll, the class serializers do not get registered at all with their associated map singleton. - if boost is linked as a dynamic lib into a user dll, the class serializers register twice with the map singleton of the polymorphic base archive. I don't want to add them here but I can provide any of the projects above to those interested. Thank you all, Bogdan ============================================================================ ============== > Hi, > I have the same scenario, and it's not a problem. > If i understand (my english is poor, sorry) well. > But there is differences: > - I use GCC compilers (but boost is portable). > - I use static linking. > Probably this differences should not have consequences on the result. > I didn't read your code... Had you follow this rules ? > - Register child class (a simple way is using the BOOST_CLASS_EXPORT > macro). > - In the serialize method of your child class, call the > serialization of parent's class (optional). I use > BOOST_SERIALIZATION_BASE_OBJECT's macro. > > If you register child class it should be ok... > Regards, > Damien. > >

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non-blocking read
by David Kaplan 21 Feb '10

21 Feb '10

I'm trying to implement a non_blocking read as follows (based on some code on the net): void util::net::set_result(optional<boost::system::error_code>* a, boost::system::error_code b) { a->reset(b); } template <typename MutableBufferSequence> optional<boost::system::error_code> util::net::read_non_blocking(ip::tcp::socket *sock, const MutableBufferSequence& buffers, int timeoutSec) { optional<boost::system::error_code> timer_result; deadline_timer timer(sock->io_service()); timer.expires_from_now(boost::posix_time::seconds(timeoutSec)); timer.async_wait(boost::bind(set_result, &timer_result, _1)); optional<boost::system::error_code> read_result; async_read(*sock, buffers, boost::bind(set_result, &read_result, _1)); sock->io_service().reset(); while (sock->io_service().run_one()) { if (read_result) timer.cancel(); else if (timer_result) { sock->cancel(); throw system_error(boost::system::error_code(errc::timed_out, get_generic_category())); } } return read_result; } I call the code as follows: util::net::read_non_blocking(Module::_socket, buffer(buf, 4), 1); (_socket is a ptr of type tcp::socket) However I'm having problems linking: undefined reference to `boost::optional<boost::system::error_code> util::net::read_non_blocking<boost::asio::mutable_buffers_1>(boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >*, boost::asio::mutable_buffers_1 const&, int) Also, what will this code return exacty?

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