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[Boost.Container] missing image in the documentation
by ilya shlyakhter 01 Apr '13

01 Apr '13

At the URL http://www.boost.org/doc/libs/1_53_0/doc/html/container/non_standard_contai… the illustration of stable vector is missing.

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How should I define a wchar_t type for use in mbtowc? [Android] [Serialization]
by Wesley Paugh 01 Apr '13

01 Apr '13

I'm attempting to port Serialization code to Android. Android-ndk-r8d does not have mbtowc implemented, which Serialization apparently uses, somewhere. I would like to recreate this function myself, rather than find another Serialization library entirely or write one myself. The function leverages the wchar_t type, which also does not appear to built into android-ndk-r8d. What is boost serialization expecting this type to be? Can I grab an implementation of it from off of a shelf somewhere?

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Problems using for_each
by Michael Powell 31 Mar '13

31 Mar '13

Hello, I am struggling making for_each work right. I am using Sourcery targeting ARM. AFAIK, GCC is actually 4.7.2, and I am flagging -std=c++11. I'm not really picky how we get for_each done (or constructs like it). I'd like to avoid "macro-expansion" for obvious reasons (i.e. debug), and the always-infamous verbosity of a for loop, if possible. I've got the following: vector<rgb_type*> all; rgb_type rgb; rgb_type rgb2 = rgb.clone(); for_each(all.begin(), all.end(), cout << _1->r() << endl); With errors: _1 was not declared in this scope. (C++ Problem) That or, void rgb_printer_func(rgb_type* prgb) { cout << prgb->r() << endl; } for_each(all.begin(), all.end(), rgb_printer_func); With errors: Invalid arguments Candidates are: #1 for_each(#0, #0, #1) (Semantic Error) Thank you. Regards, Michael Powell

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Building Boost 1.53
by Michael Powell 30 Mar '13

30 Mar '13

Hello, I believe we're on the home stretch building boost and getting productive with it. But I have a couple of questions. When we run ./b2 to build boost with the PREFIX option, what actually lands there? I'm thinking we just locate that in our /path/to/boost/, which ends up being ./tools/boost_1_53_0 from our project workspace perspective. But, there are other insights I don't know about I am certain. Thanks much. Regards, Michael Powell

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[lockfree] Queue with shared_ptr as elements
by sguazt 30 Mar '13

30 Mar '13

Hello, Is it possible to use lockfree::queue with shared_ptr as element types? For instance, ---[code]--- #include <boost/lockfree/queue.hpp> #include <boost/smart_ptr.hpp> class foobar { }; int main() { typedef boost::shared_ptr<foobar> element_type; typedef boost::lockfree::queue<element_type> queue_type; queue_type queue; } ---[/code]--- If I compile the above code I get the following error: ---[error]--- boost_lockfree_mwmr_queue.cpp:13:13: required from here ~/projects/svn/boost-trunk/boost/lockfree/queue.hpp:81:5: error: invalid application of ‘sizeof’ to incomplete type ‘boost::STATIC_ASSERTION_FAILURE<false>’ ~/projects/svn/boost-trunk/boost/lockfree/queue.hpp:85:5: error: invalid application of ‘sizeof’ to incomplete type ‘boost::STATIC_ASSERTION_FAILURE<false>’ ---[/error]--- If I use "foobar" or "foobar*" as element_type, it works. I'm using - GCC 4.7.2 with the following options enabled: -Wextra -Wall -ansi -pedantic - boost SVN trunk version Thank you very much for helping. Best, -- Marco

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[fusion] [mpl] binary mpl::transform on empty std::tuple
by Nathan Ridge 30 Mar '13

30 Mar '13

Hello, Fusion provides adaptation code for treating an std::tuple as a Fusion sequence, and adaptation code for treating Fusion sequences as MPL sequences, but it seems that in the case of a binary mpl::transform on an empty std::tuple, the two do not work well together. When trying to compile the following code: #include <boost/mpl/transform.hpp> #include <boost/mpl/back_inserter.hpp> #include <boost/mpl/vector.hpp> #include <boost/fusion/adapted/std_tuple.hpp> #include <boost/fusion/adapted/mpl.hpp> #include <boost/fusion/mpl.hpp> struct first { template <typename T, typename U> struct apply { typedef T type; }; }; int main() { typedef std::tuple<> fusion_sequence1_type; typedef std::tuple<> fusion_sequence2_type; typedef boost::mpl::transform<fusion_sequence1_type, fusion_sequence2_type, first, boost::mpl::back_inserter<boost::mpl::vector<>> >::type result_type; } I get the following errors: In file included from test.cpp:4: In file included from boost/fusion/adapted/std_tuple.hpp:13: In file included from boost/fusion/adapted/std_tuple/detail/begin_impl.hpp:10: boost/fusion/adapted/std_tuple/std_tuple_iterator.hpp:45:13: error: implicit instantiation of undefined template 'std::tuple_element<0, std::tuple<> >' : std::tuple_element<Iterator::index, ^ boost/fusion/iterator/value_of.hpp:34:28: note: in instantiation of template class 'boost::fusion::std_tuple_iterator<std::tuple<>, 0>::value_of<boost::fusion::std_tuple_iterator<std::tuple<>, 0> >' requested here struct apply : Iterator::template value_of<Iterator> {}; ^ boost/fusion/iterator/value_of.hpp:51:15: note: in instantiation of template class 'boost::fusion::extension::value_of_impl<boost::fusion::iterator_facade_tag>::apply<boost::fusion::std_tuple_iterator<std::tuple<>, 0> >' requested here : extension::value_of_impl<typename detail::tag_of<Iterator>::type>:: ^ boost/fusion/iterator/mpl/fusion_iterator.hpp:46:45: note: in instantiation of template class 'boost::fusion::result_of::value_of<boost::fusion::std_tuple_iterator<std::tuple<>, 0> >' requested here typedef typename fusion::result_of::value_of<Iterator>::type type; ^ boost/mpl/iterator_category.hpp:27:22: note: in instantiation of template class 'boost::mpl::fusion_iterator<boost::fusion::std_tuple_iterator<std::tuple<>, 0> >' requested here typedef typename Iterator::category type; ^ boost/mpl/pair_view.hpp:152:20: note: in instantiation of template class 'boost::mpl::iterator_category<boost::mpl::fusion_iterator<boost::fusion::std_tuple_iterator<std::tuple<>, 0> > >' requested here typename iterator_category<iter1_>::type ^ boost/mpl/aux_/has_tag.hpp:20:1: note: (skipping 5 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all) BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF(has_tag, tag, false) ^ boost/mpl/has_xxx.hpp:244:65: note: expanded from macro 'BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF' , boost::mpl::aux::type_wrapper<BOOST_MSVC_TYPENAME U::name>* = 0 \ ^ boost/mpl/transform.hpp:75:7: note: in instantiation of template class 'boost::mpl::fold<boost::mpl::pair_view<std::tuple<>, std::tuple<> >, boost::mpl::vector<mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::bind2<boost::mpl::push_back<mpl_::na, mpl_::na>, mpl_::arg<1>, boost::mpl::bind2<first, boost::mpl::bind1<boost::mpl::first<mpl_::na>, mpl_::arg<2> >, boost::mpl::bind1<boost::mpl::second<mpl_::na>, mpl_::arg<2> > > > >' requested here : fold< ^ boost/mpl/transform.hpp:114:1: note: in instantiation of template class 'boost::mpl::aux::transform2_impl<std::tuple<>, std::tuple<>, first, boost::mpl::back_inserter<boost::mpl::vector<mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> > >' requested here BOOST_MPL_AUX_INSERTER_ALGORITHM_DEF(4, transform2) ^ boost/mpl/aux_/inserter_algorithm.hpp:44:7: note: expanded from macro 'BOOST_MPL_AUX_INSERTER_ALGORITHM_DEF' : aux::name##_impl<BOOST_MPL_PP_PARAMS(arity, P)> \ ^ boost/mpl/eval_if.hpp:38:22: note: in instantiation of template class 'boost::mpl::transform2<std::tuple<>, std::tuple<>, first, boost::mpl::back_inserter<boost::mpl::vector<mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> > >' requested here typedef typename f_::type type; ^ boost/mpl/transform.hpp:138:1: note: in instantiation of template class 'boost::mpl::eval_if<boost::mpl::or_<boost::mpl::is_na<first>, boost::mpl::is_lambda_expression<std::tuple<> >, boost::mpl::not_<boost::mpl::is_sequence<std::tuple<> > >, mpl_::bool_<false>, mpl_::bool_<false> >, boost::mpl::transform1<std::tuple<>, std::tuple<>, first>, boost::mpl::transform2<std::tuple<>, std::tuple<>, first, boost::mpl::back_inserter<boost::mpl::vector<mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> > > >' requested here AUX778076_TRANSFORM_DEF(transform) ^ boost/mpl/transform.hpp:125:22: note: expanded from macro 'AUX778076_TRANSFORM_DEF' typedef typename eval_if< \ ^ test.cpp:21:25: note: in instantiation of template class 'boost::mpl::transform<std::tuple<>, std::tuple<>, first, boost::mpl::back_inserter<boost::mpl::vector<mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> > >' requested here typedef boost::mpl::transform<fusion_sequence1_type, ^ c++/4.8.0/tuple:672:12: note: template is declared here struct tuple_element; ^ 1 error generated. Seems like something is trying to call value_of on the begin iterator of the tuple, which in the case of an empty tuple is a past-the-end iterator. If I use non-empty tuples instead: typedef std::tuple<int> fusion_sequence1_type; typedef std::tuple<int> fusion_sequence2_type; It works fine. Unary mpl::transform works fine in either case. Am I doing something wrong, or is this a bug? Thanks, Nate

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Elegant solution to interview question about boost::fusion::vector
by Stuart 29 Mar '13

29 Mar '13

Hello everyone, I have stumbled over m2pq36bk97.fsf(a)boostpro.com in comp.lang.c++.moderated. I had never used boost before but I always try to solve interview questions. I found a solution that works, but I have the feeling that there must be a more elegant solution. The problem that was presented in the interview was the following: typedef boost::fusion::vector<int, double, float> row; std::vector<row> M; template <typename T> typename T::value_type Accumulate (T const &t) { typedef typename T::value_type value_type; return std::accumulate (t.begin (), t.end (), value_type ()); } Provide a function fun so that Accumulate (fun<0>(M)); computes the sum of the first column of M, or more generally Accumulate (fun<x>(M)); computes the sum of the xth column of M. The solution that was provided in m2pq36bk97.fsf(a)boostpro.com did not work out of the box, but I was able to fix it into the following solution: // Functor that extracts nth element of row vector. template <unsigned N> struct tuple_at { template <class Vector> typename boost::fusion::result_of::at_c<const Vector,N>::type operator()(Vector const& t) const { return boost::fusion::at_c<N, Vector>(t); } }; template <unsigned N, class M> auto fun(M const& x) -> decltype(x | boost::adaptors::transformed(tuple_at<N>())) { return x | boost::adaptors::transformed(tuple_at<N>()); } so that int main () { M.push_back(row (1, 1.0, 2.8)); M.push_back(row (2, 0.1, 2.8)); M.push_back(row (3, 0.01, 2.8)); std::cout << Accumulate(fun<1> (M)); } prints 1.11 as expected. However, I think that I should be able to achieve the same without the template tuple_at. I tried using a lambda: template <unsigned N, class M> auto fun(M const& x) -> decltype(x | boost::adaptors::transformed( [] (typename M::value_type const& x ) { return boost::fusion::at_c<N> (x); })) { auto retval = x | boost::adaptors::transformed( [] (typename M::value_type const& x ) { return boost::fusion::at_c<N> (x); }); return retval; } Unfortunately, this does not compile ("Lambda expression in an unevaluated operand"). I'm also not sure whether boost::adaptor::transformed can work with lambdas. I also tried to generate a functor object from boost::fusion::at_c using the following code from the internet: template<typename T> std::function<T> make_function (T* t) { return { t }; } template <unsigned N, class M> auto fun (M const& x) -> decltype(make_function(&boost::fusion::at_c<N, const M>)) { auto retval = make_function(&boost::fusion::at_c<N, const M> ); return retval } but this yields an error that I can't decipher yet: at.hpp:62:15: Implicit instantiation of undefined template 'boost::fusion::extension::at_impl<boost::fusion::non_fusion_tag>::apply<const std::__1::vector<boost::fusion::vector<int, double, float, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>, std::__1::allocator<boost::fusion::vector<int, double, float, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>>>, mpl_::int_<2>>' The ideal solution would be one where I don't have to write the functor object manually. Even more elegantly, I should be able to leave out the return type and let the compiler figure it out automatically. Unfortunately, I use llvm gcc 4.2, so the automatic return type evaluation is out of reach (although boost without this feature seems to be quite cumbersome). Can anyone provide some insights? Thanks in advance, Stuart

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[chrono][thread] Best way to wait?
by Klaim - Joël Lamotte 29 Mar '13

29 Mar '13

Hi, can someone clarify: 1. what is the difference between: const auto wait_time = boost::chrono::miliseconds( 8 ); boost::mutex mutex; boost::unique_lock<boost::mutex> lock( mutex ); boost::condition_variable wait_condition; wait_condition.wait_for( lock, wait_time ); and const auto wait_time = boost::chrono::miliseconds( 8 ); boost::this_thread::sleep_for( wait_time ); 2. are there other ways to wait? (I mean make the thread sleep, not looping until it's time) Joel Lamotte

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Some questions about vertex removal in subgraph
by Nicholas Mario Wardhana 29 Mar '13

29 Mar '13

Hi all, In the last few days I have been implementing partial I/O for a subgraph by saving and loading a subgraph (although actually it is only partial if we see it from the parent graph's point of view). So far, by modifying some code in Boost, I managed to save a child graph to a file, and also load two subgraphs which share a vertex without having that vertex duplicated. However, in addition to save and load, I also need to clear (i.e. remove all nodes and edges from) a subgraph, and I found that remove_vertex is not implemented; only remove_edge is. I noticed that as of now (March 2013) there is no plan to implement it [1]. I cannot use Jeremiah's suggestion there (and also in [2]) to use filtered_graph, because I need to physically remove the nodes and edges from memory, so I am thinking to implement it myself. I have a few questions about this. 1) Jeremiah said that "In particular, local vertex descriptors in subgraphs are indices into an std::vector, and so removing a vertex would invalidate many other vertex descriptors." [1] Am I right to assume that this statement is about m_global_vertex, which is of std::vector<vertex_descriptor> type? 2) Removing a vertex from a regular graph involves calling g.m_vertices.erase(..) (adjacency_list.hpp, line 1951). I found that m_vertices is also of type std::vector. So why does vertex removal work for regular graph, but supposedly not for subgraph? I use Boost version 1.53.0, and my subgraph configuration is typedef adjacency_list<vecS, vecS, undirectedS, property<vertex_index_t, int, VertexProperty>, property<edge_index_t, int, EdgeProperty> > RegularGraph; typedef subgraph<RegularGraph> Subgraph; where VertexProperty and EdgeProperty are respectively bundled properties for vertex and edge. Thank you very much! Best regards, Nicholas Mario Wardhana References: [1] https://svn.boost.org/trac/boost/ticket/4752 [2] http://boost.2283326.n4.nabble.com/Can-t-link-subgraphs-because-remove-vert…

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Re: [Boost-users] header-only libraries
by dib 27 Mar '13

27 Mar '13

> > >> I'd like to use the program_options library, but am reluctant to > >> require my users to build parts of Boost. Is there a strong > >> reason that this library cannot be header-only? > > You can build the necessary Boost CPP files as part of your own > build. > Asio (which is header-only) offers the possibility for "optional separate compilation" by including some ".../impl/src.hpp" in a source file and defining either "BOOST_ASIO_SEPARATE_COMPILATION" or "BOOST_ASIO_DYN_LINK", which very nicely lets the user choose which one suits best for his needs. Is there a reason why this isn't done for other libs like program_options, regex, etc., or has it (at least sometimes) just not been done because nobody wanted to do this extra-work? It is a very frequently asked question if/why not there is a header-only version, and although it is sometimes really not possible to make it header-only, most libs should work that way. Furthermore, in my experience specially commercial projects are reluctant to use libraries that have to be shipped with the own product, whereas it is no problem as long as they are "hidden" inside the binary.. Of course there are some disadvantages as shown in the discussion on stackoverflow, but giving the user a choice where possible should hugely increase acceptance and usage of those libraries. Greetings, dib PS: I just tried it with program_options and at least with my programs on linux it works fine, don't know how it is on other platforms or if I was just lucky: copy the src-files from libs/program_options/src to the include/boost/program_options/impl and do it "the asio-way", including the source files in a separate .cpp in my projects.. works fine and no linking is required any more.

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