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Bidirectional breadth first search?
by Amanda Robson 08 Nov '14

08 Nov '14

Hi Does anyone know if Boost already supports bidirectional breadth first search? If not, how feasible would it be to extend boost’s bfs implementation to become bidirectional? Thanks. Amanda

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iterator adaptor not inheriting pointer typedef
by Matei David 08 Nov '14

08 Nov '14

Hi, I have some questions about the Boost Iterator library. I've recently discovered the "hard way", meaning through impenetrable TMP error messages :), that when using boost::iterator_adaptor, the derived iterator type does not (always??) inherit the pointer typedef of the base iterator type. I mean, the iterator_adaptor glue class does not have this typedef. So, for example, I have a Base_Iterator type with: Base_Iterator::pointer != Base_Iterator::value_type* If I do: class Derived_Iterator : public boost::iterator_adaptor< Derived_Iterator, Base_Iterator > {...} then, strangely I find: Derived_Iterator::value_type == Base_Iterator::value_type (OK) Derived_Iterator::pointer == Base_Iterator::value_type* != Base_Iterator::pointer (not OK) I looked at the documentation, and I did find a mention of this, but only for iterator_facade, here: http://www.boost.org/doc/libs/develop/libs/iterator/doc/iterator_facade.html The corresponding page for iterator_adaptor does not mention the pointer typedef at all. While for facade using a plain pointer seems ok (no other reasonable default), I would argue that for adaptor this is not ok. Is this expected behaviour or a bug? Within the same setting, and in what could be a related issue, I also found that the intermediate boost::iterator_adaptor<> class does not seem to contain the default/common sense definition: Base_Iterator operator->() const { return this->base(); } I didn't look inside the source code of boost::iterator_adaptor, but I found a situation where I have to put this definition explicitly inside Derived_Iterator for my code to compile (without it, it doesn't). Does this sound like expected behaviour? Thanks M

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Flyweight: constexpr user defined literals
by Akim Demaille 08 Nov '14

08 Nov '14

Hi all, Hi Joaquin, I'm using flyweights of strings (aka symbols) for my "format" arguments: a key that specifies the kind of output that should be produced by the printing routines. Sometimes, I have code that roughly resembles to: print_entry_(src, dst, o, dot2tex_ ? symbol("latex") : symbol("text")); My question is: do we have constexpr constructors with Flyweight in such a way that I could have something like: print_entry_(src, dst, o, dot2tex_ ? "latex"sym : "text"sym); and have a single construction of these guys not matter how many times I go throw this piece of code, or should I build them once for all in say a member? print_entry_(src, dst, o, dot2tex_ ? sym_latex : sym_text); I've seen nothing about "constexpr" in the doc.

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Re: [Boost-users] iterator_facade Boost 1.57
by Matei David 08 Nov '14

08 Nov '14

On Tue, 04 Nov 2014 14:07:09 +0000 (UTC) gast128 wrote: > Dear all, > > Just trying out 1.57, since we are already 5 releases behind due to > all kinds of compilation errors with Boost and our software. Below > simplified code doesn't compile on vs2010: > > template <typename DerivedType> > struct IteratorFacade : public boost::iterator_facade<DerivedType, > int, std::random_access_iterator_tag> > { > typedef boost::iterator_facade<DerivedType, int, > std::random_access_iterator_tag> base; > > IteratorFacade (); > virtual ~IteratorFacade (); > > friend class boost::iterator_core_access; > > reference dereference () const; > }; > > struct MyIteratorFacade : IteratorFacade<MyIteratorFacade> > { > }; > > What do I wrong? Hi, I'm gcc 4.9.1 on Ubuntu 14.04. The reason this doesn't compile is that the "reference" typedef is contained in the glue class boost::iterator_facade, which is a base class of IteratorFacade<MyIteratorFacade>. When you write "reference" inside the later, the name is not being looked up in the base class. So you should write: typename base::reference dereference() const; If you want to use "reference" in many places in IteratorFacade<>, pull the typedef from its base with: typedef typename base::reference reference; or, if using C++11: using typename base::reference; Note: whether you pull it up or not, you can always get the typedef as IteratorFacade<...>::reference, or MyIteratorFacade::reference in your case. (See the example below, where I'm not pulling it up, but I can still find it.) I would also add the observation that your construct creates an unusual derivation. Usually, the iterator class you want to define has boost::iterator_facade as its direct base. In your case, boost::iterator_facade is the base of the base of your iterator class (so, 2 levels down): MyIteratorFacade : IteratorFacade<MyIteratorFacade> : boost::iterator_facade<MyIteratorFacade, ...> I'm not sure this would cause any problems, just be on the lookout for missing constructors. For example, this compiles just fine for me: #include <type_traits> #include <boost/iterator/iterator_facade.hpp> struct MyIteratorFacade : public boost::iterator_facade<MyIteratorFacade, int, std::random_access_iterator_tag> { typedef boost::iterator_facade<MyIteratorFacade, int, std::random_access_iterator_tag> base; MyIteratorFacade (); virtual ~MyIteratorFacade (); friend class boost::iterator_core_access; typename base::reference dereference() const; }; static_assert(std::is_same< MyIteratorFacade::value_type, int >::value, "MyIteratorFacade::value_type != int"); static_assert(std::is_same< MyIteratorFacade::reference, int& >::value, "MyIteratorFacade::reference != int&"); static_assert(std::is_same< MyIteratorFacade::pointer, int* >::value, "MyIteratorFacade::pointer != int*"); static_assert(std::is_same< std::iterator_traits<MyIteratorFacade>::value_type, int >::value, "iterator_traits<MyIteratorFacade>::value_type != int"); static_assert(std::is_same< std::iterator_traits<MyIteratorFacade>::reference, int& >::value, "iterator_traits<MyIteratorFacade>::reference != int&"); static_assert(std::is_same< std::iterator_traits<MyIteratorFacade>::pointer, int* >::value, "iterator_traits<MyIteratorFacade>::pointer != int*"); I compile with: g++ -Wall -Wextra -pedantic -std=c++11 -I${BOOST_INCLUDE_1_57} -c (I'm only using c++11 for static_assert.) M

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Boost.Python C++ pointer object to python: Attribute does not exist.
by Christoff Kok 07 Nov '14

07 Nov '14

Hi, I'm struggling with the following issue in a boost.python implementation: I have a list of std::shared_ptr in C++, I am accessing this list from Python. - When I access an element in the list, the elements does not have any attributes apparently. I get an error trying to access an attribute, hasattr returns false on the attribute, but dir informs me that it exist. - When I change the C++ implementation from shared_ptr to raw ptr's everything works as expected. - I want to use shared_ptrs for what I feel: obvious reasons. Below is the C++ code and the Python code. ################### ### garage_ext.cpp ### ################### #include<memory> #include<vector> namespace boost { template<class T> T* get_pointer(std::shared_ptr<T>& p){ return p.get(); }} struct Vehicle{ virtual ~Vehicle(){} friend bool operator==(const Vehicle& lhs, const Vehicle& rhs) { return true; } int testAttribute; }; struct Boat: public Vehicle { virtual ~Boat(){} friend bool operator==(const Boat& lhs, const Boat& rhs) { return true; } int testBoatAttribute; }; struct Garage { friend bool operator==(const Garage& lhs, const Garage& rhs) { return true; } std::vector<std::shared_ptr<Vehicle>>& vehicleList() { return m_VehicleList; } std::vector<std::shared_ptr<Boat>>& boatList() { return m_BoatList; } std::vector<std::shared_ptr<Vehicle>> m_VehicleList; std::vector<std::shared_ptr<Boat>> m_BoatList; }; #include <boost/python.hpp> #include <boost/python/suite/indexing/vector_indexing_suite.hpp> class BoatWrap : public Boat, public boost::python::wrapper<Boat> { public: static std::shared_ptr<Boat> cast(std::shared_ptr<Vehicle> const& v) { return std::dynamic_pointer_cast<Boat>(v); } }; BOOST_PYTHON_MODULE(garage_ext) { using namespace boost::python; class_<Garage>("Garage") .def("vehicleList", &Garage::vehicleList, return_internal_reference<1>()) .def("boatList", &Garage::boatList, return_internal_reference<1>()) ; class_<Vehicle, std::shared_ptr<Vehicle>,boost::noncopyable>("Vehicle", no_init) .def_readwrite("testAttribute", &Vehicle::testAttribute) ; class_<BoatWrap,std::shared_ptr<Boat>,bases<Vehicle>>("Boat") .def("cast", &BoatWrap::cast) .staticmethod("cast") .def_readwrite("testBoatAttribute", &Boat::testBoatAttribute) ; implicitly_convertible<std::shared_ptr<Boat>,std::shared_ptr<Vehicle>>(); class_<std::vector<std::shared_ptr<Vehicle>> >("stl_vector_Vehicle_ptr") .def(vector_indexing_suite<std::vector<std::shared_ptr<Vehicle>> >()); class_<std::vector<std::shared_ptr<Boat>> >("stl_vector_Boat_ptr") .def(vector_indexing_suite<std::vector<std::shared_ptr<Boat>> >()); } ##################### ### Python test code ### ##################### g = Garage() l = g.boatList() newboat = Boat() l.append(newboat) boatFromList = l[0] print(type(boatFromList)) print(str(hasattr(newboat,"testBoatAttribute"))) dir(boatFromList) # The following line throws the error. print(str(hasattr(boatFromList,"testBoatAttribute"))) I created a cast method for boat. If I cast l[0] to Boat using: boatFromList = Boat.cast(l[0]) print(str(hasattr(boatFromList,"testBoatAttribute"))) works. This is all very strange to me. It feels very buggy. Could someone please help me clarify the reason for this behavious? Regards, Christoff

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reference_wrapper on Boost 1.57
by gast128 07 Nov '14

07 Nov '14

This gives also a compilation error on vs2010: void F() { boost::reference_wrapper<float (* const)(float)> wrap(&cosf); //std::reference_wrapper<float (* const)(float)> wrap(&cosf); //ok } 1>KTestCuj2005June1.cpp(182): error C2248: 'boost::reference_wrapper<T>::reference_wrapper' : cannot access private member declared in class 'boost::reference_wrapper<T>' 1> with 1> [ 1> T=float (__cdecl *const )(float) 1> ] 1> C:\work sdk\boost_1_57_0\boost/core/ref.hpp(85) : see declaration of 'boost::reference_wrapper<T>::reference_wrapper' 1> with 1> [ 1> T=float (__cdecl *const )(float) 1> ] ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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Boost on Google+
by Vladimir Prus 07 Nov '14

07 Nov '14

Hi, I've created a Google+ community for Boost, and everybody is welcome to join here: https://plus.google.com/communities/106814259809358442744 I don't have any great plan here, but a lot of tech people are active on G+, so why not? -- Vladimir Prus CodeSourcery / Mentor Embedded http://vladimirprus.com

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boost 1.57: MS VS2008: unknown pragma in type_index.hpp
by Andreas Wehrmann 06 Nov '14

06 Nov '14

Hi! I've just compiled boost 1.57 with MS VS2008 x86 and this warning came all over the place: main\lib\boost_1_57_0\boost\type_index.hpp(37) : warning C4068: unknown pragma Still, the compilation went fine and everything seems to work as usual. It's just somewhat annoying because this warning pops up very often when I compile my applications. Regards, Andreas

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[Optional] Possible bug with VS2008
by dariomt＠gmail.com 05 Nov '14

05 Nov '14

Hi, The following minimal test case does not compile with VS2008 (using Boost 1.55) #include <boost/optional.hpp> struct A { int T; }; int main() { boost::optional<A> a; } The error is, edited for clarity: boost\optional\optional.hpp(479) : error C2523: 'A::~T' : destructor tag mismatch boost\optional\optional.hpp(479) : while compiling class template member function 'void boost::optional_detail::optional_base<T>::destroy_impl(boost::optional_detail::optional_base<T>::is_not_reference_tag)' with [ T=A ] boost\optional\optional.hpp(500) : see reference to class template instantiation 'boost::optional_detail::optional_base<T>' being compiled with [ T=A ] main.cpp(8) : see reference to class template instantiation 'boost::optional<T>' being compiled with [ T=A ] After much head-scratching, I found out the culprit: the name of the integer member!! The compiler confuses the name of member 'T' with the name of the template parameter 'T' when trying to invoke its destructor... The offending code is void destroy_impl ( is_not_reference_tag ) { get_ptr_impl()->T::~T() ; m_initialized = false ; } Given that I cannot change struct A, is there a way to fix this? Is this a compiler bug or a Boost.Optional bug? Thanks in advance!

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Spirit with UI Tools
by Philipp Kraus 05 Nov '14

05 Nov '14

Hello, I would like to create a small parser with Boost.Spirit. I have run the short examples and everything works well, so I would like to create my own LL grammar. In my case I need also for documentation a EBNF or something else and in the best case I can would like to create the EBNF first and transform this into the Spirit LL grammar code. Did you know any tools to do this? My first idea is to use AntLR to create the grammar but imho it creates a LR grammar. Can you recommend a tool to define the grammar structure and generate the Spirit code? Thanks a lot Phil

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