February 2010 - Boost-users

Detect typedef in class
by Hansjoerg 25 Feb '10

25 Feb '10

Hello, is there some way to detect if a class has an typedef with boost 1.34.1? I want to detect typedef T value_type; in a class... Thanks Hansjörg

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[phoenix] How to determine if a phoenix functor is callable?
by Jesse Perla 25 Feb '10

25 Feb '10

So there any ways to implement a metafunction can_be_called on a phoenix functor s.t.: auto f = _1 + _2; static_assert(is_callable<decltype(f), double, double>::value, ""); static_assert(!is_callable<decltype(f), double, NonArithmeticType>::value, ""); static_assert(!is_callable<decltype(f), double>::value, ""); //Needs 2 args A while back, I was pointed towards the following from proto to determine if a functor was callable: http://www.boost.org/doc/libs/1_42_0/doc/html/proto/appendices.html#boost_p… pendices.implementation.function_arity This seemed to work well for most of my custom built functors, but as far as I can tell, the trick doesn't work for either boost::lambda or boost::phoenix functors (or std::tr1::bind for that matter). I can post a test case for phoenix if people think that it should work. -Jesse

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[karma] Losing attribute?
by Sebastian Redl 25 Feb '10

25 Feb '10

Hi, I've got a Karma generator that should emit a vector of records, writing out the index of every entry at the start. My code looks like this (note that GEOPOINT is a fusion-adapted struct of two doubles): typedef std::vector<GEOPOINT> Contour; typedef std::vector<Contour> Poly; rule<Iterator, GEOPOINT()> point; rule<Iterator, Contour(int)> contour; rule<Iterator, locals<int>, Poly()> polygon; rule<Iterator, Poly()> start; point = L';' << double_ << L';' << double_; contour = L";SUBPOLYGON " << lit(_r1 - 1) << L" POINTS " << lit(phoenix::size(_val)) << L" MASK XOR" << *point; polygon = L"POLYGON COUNT " << lit(phoenix::size(_val)) << *(contour(_a)[++_a]); start = polygon; This doesn't work. If I take away the modification of _a, it works, except that of course the index is 0 in every iteration. But the moment I modify _a in any way (including assigning to it anywhere in the polygon rule), suddenly contour seems to get an incorrect attribute: it never fails, but never emits points either, i.e. I get an endless string of ";SUBPOLYGON 1 POINTS 0 MASK XOR;SUBPOLYGON 2 POINTS 0 MASK XOR;SUBPOLYGON 3 POINTS 0 MASK XOR...". Any idea why that is? Sebastian

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[program_options] Parsing Config File
by Christian Meesters 25 Feb '10

25 Feb '10

Hi, I'd like to use/abuse boost::program_options to parse a configuration file like this: [project1] parameter=x ... [project2] parameter=y ... [project3] parameter=z ... and so on. Point is that I cannot now how many 'project' entries there will be in advance. Is there a way to parse this and retrieve a list of project keys from boost::program_options::variables_map? Or (the 'abuse' above already suggested that I'm not certain whether this library is the most suited one) is there a better approach? Christian

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[MPL] Filtering a sequence to leave only most-derived types
by Sebastian Redl 25 Feb '10

25 Feb '10

Hi, I've got an MPL sequence containing a (rather small) number of classes. I want to filter this sequence so that all classes that are a base of another class in the sequence are filtered out. I thought I'd do something like this (in pseudo-code): is_strict_base_of(Base, Derived) = !is_same(Base, Derived) && is_base_of(Base, Derived) Result = remove_if( Interfaces, find_if( Interfaces, is_strict_base_of(outer_value, inner_value) ) != end(Interfaces) ) where outer_value is the iteration value of the remove_if loop, and inner_value is the iteration value of the count_if loop. Yes, this is N², but since the length of the initial sequence is very unlikely to exceed 8, I can live with that. In MPL syntax: template <typename Base, typename Derived> struct is_strict_base_of : mpl::and_< mpl::not_<boost::is_same<Base, Derived> >, boost::is_base_of<Base, Derived> > {}; typedef typename mpl::remove_if< Interfaces, // Remove from Interfaces mpl::not_<mpl::equal< mpl::find_if< Interfaces, // if there is any value in interfaces // that this is a base of is_strict_base_of<???> >, mpl::end<Interfaces> > > >::type Bases; How do I represent outer_value and inner_value in this expression? It seems I can't simply put mpl::_1 and mpl::_2 there, since that gives me a static assertion failure (argument is not available). I think I have to put an apply somewhere in there, but I can't figure out where. Sebastian

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accessing a pair<> element of multi_index container, uniquely ordered
by Andrew Kokkalis 25 Feb '10

25 Feb '10

I have the following problem using a multi index container which is uniquely ordered on a pair <int,int>. Each time i want to find every pair i that contains a specific integer. The other value of the pair is irrelevant. An example: <0,1> <0,2> <0,3> <1,2> <1,3> <2,3> and I want to find all the pairs with the value 0 as the first integer. function find() wants the whole pair and iterator find(const CompatibleKey& x,const CompatibleCompare& comp)const; doesn't help ,too. * **Here is the declaration of my container** typedef pair<int, int> clusterset; struct cluster { clusterset pair; float distance; cluster(clusterset pair, float distance) : pair(pair), distance(distance) {} }; struct cluster_pair{}; struct cluster_distance{}; typedef multi_index_container< cluster, indexed_by< ordered_unique< tag<cluster_pair>, BOOST_MULTI_INDEX_MEMBER(cluster, clusterset, pair)>, ordered_non_unique< tag<cluster_distance>, BOOST_MULTI_INDEX_MEMBER(cluster, float, distance)> > > cluster_index;* Any ideas?

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Re: [Boost-users] [serialization] Polymorphic serialization withpolymorphic archives problem...
by Bogdan 25 Feb '10

25 Feb '10

Robert Ramey <ramey <at> rrsd.com> writes: > > > > ================================================== > > What is worrisome though, isomorphic serialization of > > polymorphic_derived1 as an object followed by polymorphic > > serialization through a pointer to the base class FAILS WITH ACCESS > > VIOLATION: > > > > > > ================================================== > > Isomorphic serialization of a class not related to the hierarchy as > > an object followed by polymorphic serialization through a pointer to > > the base class WORKS AS EXPECTED. > > I'm not sure what the above means. > I hoped this would help narrow the 'access violation' issue: - mixing isomorphic and polymorphic serialization seems to be problematic whenever the object using isomorphic serialization is also a part of the hierarchy for which we use polymorphic serialization. - on the other hand, if the object belongs to a totally independent class we do not have this issue. Is it possible this is also related to the registration of serializers? Bogdan

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how can I use jamfile complie WinMain?
by l.jay Yuan 25 Feb '10

25 Feb '10

how can I use jamfile complie WinMain? my cpp code: #include <windows.h> int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) { return 0; } my jamfile: exe main : [ glob-tree *.cpp *.c : .svn ] ; install . : main : <install-type>EXE ; compile use msvc7.1, I got error LNK2019(___tmainCRTStartup) can bjam do it? someone help me, please, thanks vey much!!!

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message_peek
by David Kaplan 25 Feb '10

25 Feb '10

How do I perform a peek instead of a read (which removes data from the buffer)? I found socket_base::message_peek, how do I use that together with my socket and asio::read()?

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Re: [Boost-users] [serialization] Polymorphic serialization withpolymorphic archives problem...
by Martin Lederhilger 25 Feb '10

25 Feb '10

Hello Robert, hello Bogdan, I have quite the same problem (Exception multiple_code_instantiation thrown in basic_serializer_map.cpp at line 48) as Bogdan. It can be reproduced by changing the pointer type from polymorphic_base to polymorphic_derived2 in the original test_dll_exported.cpp example, which comes with the library. void save_exported(const char *testfile) { test_ostream os(testfile, TEST_STREAM_FLAGS); test_oarchive oa(os, TEST_ARCHIVE_FLAGS); polymorphic_base *rb1 = new polymorphic_derived1; polymorphic_derived2 *rb2 = new polymorphic_derived2; // export will permit correct serialization // through a pointer to a base class oa << BOOST_SERIALIZATION_NVP(rb1); oa << BOOST_SERIALIZATION_NVP(rb2); delete rb1; delete rb2; } I think the problem is that when oa << BOOST_SERIALIZATION_NVP(rb2); is called, that the system registers an type in oserializer.hpp, which leads to creation of the singletons also in the executeable. I have this problem when serializing a shared_ptr<A> in class B in B.dll to an object of class A in A.dll. I tried to simply comment out this check, but it seems that I get problems with tracking later. I have a class hierarchy like this: C derives from B derives from A. A has a weak_ptr<A> to itself (something like boost::enable_shared_from_this). If I serialize an object of type C via a base pointer of type B the serialization walks like this: C::serialize, B::serialize, A::serialize, and again C::serialize (with a wrong this pointer - and it should not do that). Maybe my second problem depends on the first one. I hope that my report can be of help. Thanks in advance for your answers, Martin Lederhilger

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