September 2010 - Boost-users - lists.preview.boost.org

[Serialization] compilation error on boost/serialization/item_version_type.hpp
by Paul Graphov 22 Sep '10

22 Sep '10

Hello Boost Users, File mentioned in subj (included via boost/serialization/vector.hpp -> /boost/serialization/collections_save_imp.hpp) fails to compile at my Ubuntu box because of blatant use of assert function. Problem was solved by including <boost/assert.hpp> and changing assert to BOOST_ASSERT Is it a bug or just my misconfiguration? Thanks.

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Unresolved overloaded function type with local_time and function
by Nevin Liber 21 Sep '10

21 Sep '10

I'm getting the dreaded "unresolved overloaded function type" error on the following line of code: boost::function<boost::posix_time::ptime()> fn(boost::posix_time::microsec_clock::local_time); If I wrap the call to local_time() in a function or a function object, it works without any issues. I don't see any other overloads for local_time(). I'm sure it's something simple I'm just not seeing... -- Nevin ":-)" Liber <mailto:nevin@eviloverlord.com> (847) 691-1404

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[Proto]: How to use complex grammars in a domain/extension
by Roland Bock 21 Sep '10

21 Sep '10

Hi, I am trying to create a DSEL with Boost.Proto, which (among other things) should allow expressions like i == j + 3 && t != "foo" and want to prevent disallowed operators to be generated by Proto. Please consider the code below. // ----------------------------------------------------------------------- #include<boost/proto/proto.hpp> using namespace boost; typedef proto::terminal<int>::type terminal; struct addition: proto::or_ < terminal, proto::plus<addition, addition> > {}; struct equation: proto::equal_to<addition, addition> {}; struct condition: proto::or_ < equation, proto::logical_and<equation, equation> > {}; template<class Expr> struct extension; struct my_domain: proto::domain < proto::pod_generator< extension>, condition > {}; template<class Expr> struct extension { BOOST_PROTO_EXTENDS( Expr , extension<Expr> , my_domain ) }; int main() { terminal c; BOOST_PROTO_ASSERT_MATCHES(c + c, addition); // OK BOOST_PROTO_ASSERT_MATCHES(c == c, equation); // OK BOOST_PROTO_ASSERT_MATCHES(c == c, condition); // OK BOOST_PROTO_ASSERT_MATCHES(c == c&& c == c, condition); // OK extension<terminal> i; // I was hoping for the following to be legal i + i; // ERROR: operator+ not found i == i; // ERROR: operator== not found i == i&& i == i; // ERROR: operator== not found } // ----------------------------------------------------------------------- In my_domain, I can replace condition by addition, which allows i + i, but then the == operator is still missing (and the &&, too, probably). How can I solve this? Thanks and regards, Roland

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How to write a predicate for mpl::find_if that is able to work with placeholders?
by Michael Schulze 21 Sep '10

21 Sep '10

Hi list, I have a problem that bothers me since days. It seems, that I am always doing something wrong. I try to write a meta function, that is able to work with placeholders and is applicable to mpl::find_if. I understand the example from the documentation where is_same is used, which is in my understanding also a meta function. is_same gets always the current element of the sequence and compares it with the type given as second template argument to itself. Correct me if I am wrong at this point. So far so good, what I need is not the comparison to the type but instead a comparison with an encapsulated type, a kind of tag type if you want. Here is my class template template<int i> struct Slot { typedef Slot type; typedef int_<i> slot_id; }; and I would like to test whether a certain slot_id is contained within a sequence, because the Slot class template may have different further template arguments, here omitted for the sake of clarity. My created meta function is: template<typename A, typename B> struct contained : is_same< typename A::slot_id ,B> {}; A possible sequence may be defined as: typedef vector<Slot<0>, Slot<10>, Slot<15> > slots; and the find_if's invocation should look like this typedef find_if<slots, contained< _1, int_<10> > >::type t10; and a comparison with the dereferenced returned iterator should give true BOOST_MPL_ASSERT(( is_same< deref<t10>::type, Slot<10> > )); However, until now I have not much luck with my different tries because I get always compile errors that state that the mpl::arg<1> did not has slot_id type. This is totally right, however, how I reach it that not the placeholder is given to the meta function but instead the current element of the sequence to which the iterator points and for which the placeholder is a substitute. If I reflect it seems I have not fully understand how the placeholder mechanism works in detail but I would like to get it. Okey, I have two solution that work and give me the correct result for my problem. I created two different "contained" definitions and find_if invocations 1. version: template<typename Nr> struct contained1 { template <typename Slot> struct apply : ::boost::is_same< typename Slot::slot_id, Nr > {}; }; typedef find_if<slots, contained1<int_<10> > >::type t11; 2. version: struct contained2 { template<typename A, typename B> struct apply : is_same< typename A::slot_id,B>::type {}; }; typedef find_if<slots, bind< contained2, _1, int_<10> > >::type t12; Both versions work, because they are meta function classes, but the invocation of find_if and how the parameter is delivered to the predicate is not clear at least in the first version. In the second version this is clear but we need an additional bind. Is there a way, to get my initial version working, and to use a meta function instead of a meta function class. In my eyes, my initial find_if invocation is clearer and more readable e.g. for maintainers. Thanks and regards Michael

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graph: PropertyMap needs lvalue for vertex_index
by Jens Weller 21 Sep '10

21 Sep '10

Hi, I've been playing arround with boost::graph (and the layout algorithms in special). Now I encountered a little problem, I'm trying to get Kamada Kawai Spring to work, but I do get an compile error when calling put for vertex_index. So, this problem has nothing to do with KKS. My Code: typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, // Vertex properties boost::property<boost::vertex_index_t, int, boost::property<vertex_position_t, point> > // Edge properties ,boost::property<boost::edge_weight_t, double> > Graph; Graph g(scene->getNodeCount()); boost::graph_traits<Graph>::vertex_iterator vi,vi_end; int i = 0; for (boost::tie(vi, vi_end) = boost::vertices(g); vi != vi_end; ++vi) boost::put(boost::vertex_index, g, *vi, i++); put throws now a compile Error: ..\..\..\cpp\boost_1_43/boost/property_map/property_map.hpp:361: error: lvalue required as left operand of assignment The last argument of put does throw this error. I expected the code to work, as I have copied it out of the layout_tests file: http://www.boost.org/doc/libs/1_43_0/libs/graph/test/layout_test.cpp So, where is my error here? I tried some different versions and some casts, but none made this code work. And I don't think that something that trivial is broken in the testcases. regards, Jens Weller -- GRATIS: Spider-Man 1-3 sowie 300 weitere Videos! Jetzt freischalten! http://portal.gmx.net/de/go/maxdome

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this_thread::get_id() never returns occasionally
by Samuel Williams 21 Sep '10

21 Sep '10

Hi, I'm running boost on an iPhone 3G compiled with the official 3.2 SDK on a regular iPhone (i.e. not jailbroken). Sometimes I get a strange situation where calling this_thread::get_id() never returns. #0 scoped_lock [inlined] () at spinlock_gcc_arm.hpp:45 #1 boost::detail::spinlock::lock () at boost_1_44_0/boost/smart_ptr/detail/spinlock_pool.hpp:41 #2 boost::detail::sp_counted_base::weak_add_ref () at spinlock_gcc_arm.hpp:61 #3 atomic_increment [inlined] () at boost_1_44_0/boost/smart_ptr/detail/sp_counted_base_spin.hpp:364 #4 0x000b6c38 in boost::(anonymous namespace)::make_external_thread_data () at spinlock_gcc_arm.hpp:189 #5 0x000b849c in boost::this_thread::get_id () at libs/thread/src/pthread/thread.cpp:189 Is this a bug? Kind regards, Samuel

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[lexical_cast] Canonical representation for numbers?
by Francesco Biscani 21 Sep '10

21 Sep '10

Hello, does lexical_cast make some kind of guarantees on the output of arithmetic types cast as strings? I'm asking because I need to pass a lexical representation of integers and floats to the constructors of some 3rd party class that expects as input strings containing a certain representation of numbers. E.g., a float represented as string must be either in decimal or scientific notation, with "." as separator, "e" or "E" preceding the exponent, leading sign only in case of negative numbers and so on. So far I've used successfully lexical_cast for such purposes, but I'm wondering if other factors (e.g., locale) could alter the string representation of numbers. Is it safe to assume all numbers will always be cast in the same string structure regardless of platform, i18n, etc.? Cheers, Francesco.

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has_trivial_copy for optimization
by Hite, Christopher 21 Sep '10

21 Sep '10

I noticed poor performance coping a structure with a bunch of optionals. The reason is the cost of checking if the optionals are set. CPU's hate branching it breaks their pipelining. if(that->a) this->a=*that->a; At the end of the day I just wrote a copy construct which does a memcpy(), since the data types were just POD. It makes me a bit nervous since my code might break with a different impl of opitonal. Then I thought hey wouldn't it be cool if defined a metafunction that specified memcpy/memmove are allowed? It looks like has_trivial_copy<> fits the bill. // Suggested code: namespace boost{ template<typename T> struct has_trivial_copy< boost::optional<T> > : has_trivial_copy<T> {}; }//namespace boost typedef boost::optional<int> OptionalInt; BOOST_STATIC_ASSERT(( has_trivial_copy<OptionalInt>::value )); //fixed thanks to code above struct SomeOptionals{ OptionalInt a,b;}; BOOST_STATIC_ASSERT(( has_trivial_copy<SomeOptionals>::value )); //fails The second test fails. It can't imagine how to make it work without some compiler magic. I wonder if a compiler could use metafunctions to know which optimizations were legal. Similar meta function specializations could be written for boost::variant and boost::fusion::map. I could imagine contains like std::vector using this to do memmove() for example. Chris

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Using Boost.Spirit with Boost.Units
by Vitaly Budovski 21 Sep '10

21 Sep '10

Hi, I need to be able to construct expressions from a collection of basic units and prefixes. The expression is provided as a string and thus needs to be parsed first. I have been able to achieve without too much trouble. What I am having trouble with is constructing the appropriated expressions using the Boost.Units library. I'm still very new to these two boost libraries so any pointers on how to achieve what I'm after (is it possible?) would be very much appreciated. Please see my code below: ----------------------------------- #include <boost/spirit/include/phoenix.hpp> #include <boost/spirit/include/qi.hpp> #include <boost/units/systems/si.hpp> #include <boost/units/systems/si/prefixes.hpp> #include <boost/units/systems/cgs.hpp> #include <boost/units/systems/temperature/celsius.hpp> #include <boost/variant.hpp> #include <iostream> #include <string> using namespace boost::units; using namespace boost::units::si; // Most prefixes omitted for brevity. struct si_prefix_symbol_: boost::spirit::qi::symbols<char, int> { si_prefix_symbol_() { add ("k", 3) ("M", 6) ("G", 9) ("c", -2) ("m", -3) ; } } si_prefix_symbol; typedef boost::variant<quantity<cgs::mass>, quantity<length>, quantity<si::time>, quantity<absolute<si::temperature> >, quantity<absolute<celsius::temperature> >, double> variant_t; struct unit_symbol_: boost::spirit::qi::symbols<char, variant_t> { unit_symbol_() { add ("m", 1.0 * meter) ("g", 1.0 * cgs::gram) ("s", 1.0 * second) ("K", 1.0 * absolute<si::temperature>()) ("C", 1.0 * absolute<celsius::temperature>()) ; } } unit_symbol; template<class Iterator> struct unit_expression: boost::spirit::qi::grammar<Iterator, variant_t()> { unit_expression(): unit_expression::base_type(start) { using boost::spirit::int_; using boost::spirit::ascii::space; using boost::spirit::eps; using namespace boost::spirit::arg_names; start = eps[_val = 1.0] >> ( ( ( unit_symbol | si_prefix_symbol >> unit_symbol ) >> -( '^' >> int_ ) ) % space ) ; } boost::spirit::qi::rule<Iterator, variant_t()> start; }; int main() { std::string in("kg m^-2"); typedef std::string::const_iterator iterator_type; typedef unit_expression<iterator_type> unit_expression; iterator_type first = in.begin(); iterator_type last = in.end(); unit_expression unit_parser; variant_t result; bool r = parse(first, last, unit_parser, result); if(r && first == last) { std::cout << "success: " << result << std::endl; } else { std::cout << "parsing failed at: "; std::cout << std::string(first, last) << std::endl; } return 0; }

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[multi_array] pointer type - does not compile
by Suresh Kumar 21 Sep '10

21 Sep '10

Hi The following code does not compile. #include <boost/multi_array.hpp> #include <iostream> int main () { typedef boost::multi_array<int, 3> array_type; typedef array_type::index index; array_type * A; A = new array_type(boost::extents[3][4][2]); array_type::extent_gen extents; A[0][0][0] =1; return 0; } gives large number of errro messages of which some are given below. /usr/include/boost/multi_array/concept_checks.hpp:92: error: ‘int’ is not a class, struct, or union type /usr/include/boost/multi_array/concept_checks.hpp:71: error: using invalid field ‘boost::detail::multi_array::ConstMultiArrayConcept<Array, NumDims>::id’ I am using a pointer type because, the size of the multi_array is only known at run time and I want the multi_array to be a private data element of a class so that the methods can store data in my multi_array. Thanks for suggestions suresh -- R Suresh Kumar, http://www.ee.ucr.edu/~sramachandranna Sarve bhavantu sukinaha (May everyone be happy) Sarve santu niramiyaha (May everyone be without affliction) Sarve bhadrani pashyantu (May everyone see only goodness) Ma kashchit dukha bhak bhavet (Let none be the victim of suffering)

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