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safe check if lockfree::queue is empty
by niXman 02 Apr '13

02 Apr '13

Hi, I read the docs about lockfree::queue::empty() and understang what this way is not safe in multithreaded program. The question is, how can I verify that the queue is empty? Will it be correct the following code? bool empty() { T *tmp = 0; if ( queue.pop(tmp) ) { queue.push(tmp); return false; } return true; } Thanks. -- Regards, niXman ___________________________________________________ Dual-target(32 & 64-bit) MinGW compilers for 32 and 64-bit Windows: http://sourceforge.net/projects/mingwbuilds/ ___________________________________________________ Another online IDE: http://liveworkspace.org/

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Good lock_guard<mytype> example
by Michael Powell 02 Apr '13

02 Apr '13

Hello, The pattern goes something like this: boost::lock_guard<mytype> guard(*this). However, compiler is asking for a lock or unlock. I don't know what this is, or what it should be. Thank you... Regards, Michael Powell

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Newbie Interprocess message_thread user
by John Davies 01 Apr '13

01 Apr '13

I'm new to Boost and new to Linux. But old to Windows. So I'm doing some initial development in Windows XP. I have two executables made in different projects. I planned on using a message_queue to communicate between the two applications. But sending a message from one app does not make it to the other. I can add and handle messages from one thread to another within the same application. SO I know I have things partially setup correctly. But now I'm at a complete loss. Should two exe files be able to communicate through Boost message_queues? Or am I misunderstanding the whole thing?

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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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