September 2008 - Boost-users - lists.preview.boost.org

boost::multi_index help
by Axel 18 Sep '08

18 Sep '08

I'm trying to use multi_index to store objects pointers. These objects have mainly 3 fields : - string name - int id - int block_id name & id are unique among all instances, but block_id can be the same for many instances. I want to distribute the object instances among a few blocks, so many instances can have block_id 0, many others block_id 1, and so on. (there are 6 blocks for the moment) here is my struct : /* tags */ struct name_{} ; struct id_{} ; struct block_id_{} ; typedef hashed_unique< tag<name_>, boost::multi_index::mem_fun<Foo, string, &Foo::getName> > NameIndex ; typedef ordered_unique< tag<id_>, boost::multi_index::mem_fun<Foo, int, &Foo::getId> > IdIndex ; typedef ordered_non_unique< tag<block_id_>, boost::multi_index::mem_fun<Foo, int, &Foo::getBlockId> > BlockIndex ; typedef multi_index_container<Foo*, indexed_by<NameIndex, IdIndex, BlockIndex> > FooList ; The name & id indexes work well but I dont manage to get the Foo* pointers for a given block_id. I m using : foo_list_.get<block_id_>().find(1) to grab the wanted list. My problem is that in the result I have not only Foo instances from the block 1. This is what I get when I try to query for a given block_id : For block 5 : only objects with block_id == 5 For block 4 : objects with block_id == 4 and 5 For block 3 : objects with block_id == 3, 4 and 5 For block 2 : objects with block_id == 2, 3, 4 and 5 and so on. I d like to get only the objects with block_id = 4 when I query the multi_index object on its block_id index. I now wonder if what I want to do can be done with multi_index. Thanks in advance for your help

2 2

Cross-Compile Boost for Embedded Linux
by Richard Ketcham 18 Sep '08

18 Sep '08

Hi everyone, Here is my question: what do I have to do to cross-compile boost with this compiler? Right now, the libraries and files associated with threading are the most important to me. I am starting to work with boost at the behest of a coworker. My goal is to get boost compiled for an embedded linux environment. My current setup includes my desktop running Ubuntu which also hosts the buildroot for the embedded linux environment. I have downloaded boost_1_36_0.tar.bz2 and have extracted it to /usr/local/boost_1_36_0/. For the sake of simplicity, let's say that the compiler for the embedded linux environment resides at .../staging_dir/bin/arm-linux-gcc-4.1.1 Thanks in advance for your help. Rich -- There is nothing more practical than a good theory. James Maxwell

4 11

static reflection
by James Pritts 18 Sep '08

18 Sep '08

On a boost thread a while ago, I saw some code to query for the existence of a member function of a class using SFINAE and BOOST_STATIC. I guess you could call it static reflection. Below is a code snippet that does not work using the aforementioned methods. The culprit is the using Base::operator() statement in the Derived class. Apparently the base class method void operator()(float u) is not part of the type of Derived. This was a shock to me, because you can call the overloaded method from the derived class. I'd appreciate any advice on how to check for the existence of member functions in this scenario. I fear it may be impossible. Thanks! #include <iostream> #include <boost/shared_ptr.hpp> typedef char (&no_tag)[1]; typedef char (&yes_tag)[2]; template <typename Class, typename R, typename Arg1, R(Class::*)(Arg1)> struct HasExactSignature { }; template<typename Class, typename R, typename Arg1> no_tag doesVisitorImplementHelper(...); template<typename Class, typename R, typename Arg1> yes_tag doesVisitorImplementHelper(HasExactSignature<Class, R, Arg1, &Class::operator()>* p=0); template<typename Class, typename R, typename Arg1> struct DoesVisitorImplement { BOOST_STATIC_CONSTANT(bool, value = sizeof(doesVisitorImplementHelper<Class,R,Arg1>(0)) == sizeof(yes_tag)); }; struct Base { void operator()(float u) { std::cout << "aaaa"; } }; struct Derived : public Base { using Base::operator(); void operator()(int u) { std::cout << "bbbb"; } }; int main() { std::cout << DoesVisitorImplement<Derived,void,int>::value << std::endl; std::cout << DoesVisitorImplement<Derived,void,float>::value << std::endl; return 0; }

2 1

dynamic link error: boost::program_options::arg not found
by Sebastian Hauer 17 Sep '08

17 Sep '08

Hi, I am trying to dynamically link one of my *libraries* to boost program_options on windows with msvc-8.0 but linking fails due to a missing symbol. Quickly googling for this problem revealed no resolution to my problem, although it appears other people ran into this issue before. Did anyone resolve it or is everyone linking boost program_options statically? I initially ran into this issue on boost 1_34_1 but have since upgraded to 1_36 hoping it would have gotten fixed with no luck. error LNK2001: unresolved external symbol "class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > boost::program_options::arg" (?arg@program_options@boost@@3V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A) Here is the link command line: link /NOLOGO /INCREMENTAL:NO /DLL /DEBUG /subsystem:console /out:"foo.dll" /IMPLIB:"foo.lib" /LIBPATH:"..\boost_1_36_0\lib.x86-nt-msvc8" @"foo.dll.rsp" And foo.dll.rsp contains besides the name of my object files also references to the following external import libraries: "boost_date_time-vc80-mt-gd-1_36.lib" "boost_filesystem-vc80-mt-gd-1_36.lib" "boost_program_options-vc80-mt-gd-1_36.lib" "boost_system-vc80-mt-gd-1_36.lib" Thanks, Sebastian

2 2

Is there a parameter to build without compiler version info in the target library name?
by Bill David 17 Sep '08

17 Sep '08

By default, the compiled library have a name like: libboost_thread-gcc41-mt.a but I don't want the gcc41 information in the name as I may need modify my makefile to switch to another environment with gcc4.3. So is there a parameter in bjam to suppress the compiler version info in target library name? Or how will you solve this kind of problem?

3 2

Looking for tangent of an arbitrary 2d curve.
by Atanassov Tervel-PT1672 17 Sep '08

17 Sep '08

Hello, I am looking for code which will approximate the tangent at a point of an arbitrary 2D curve. Does boost have such functionality? Thanks, Tervel Atanassov

1 0

[fusion] How to transform types of fusion::map ?
by Zeljko Vrba 17 Sep '08

17 Sep '08

A very concrete question: I have map<pair<K1, V1>, pair<K2, V2>, ..> as input. How do I produce map<pair<K1, std::vector<V1> >, pair<K2, std::vector<V2>, .. > on output? I do not see an equivalent of LISPs MAPCAR in the list of algorithms.. Is this something that should be done by combining fold and push_back algorithms? If so, I'm currently in the dark on how to do it (no example for the fold metafunction algorithm) === Few more questions now that I'm already posting: - what is the difference between accumulate and fold? - what is the purpose of for_each metafunction when the docs say that it always returns void? (and no side-effects are possible at compile-time) Thanks.

4 4

Problem with iterator_facade
by Robert Dailey 17 Sep '08

17 Sep '08

Hi, I have the following iterator_facade class: class PassIterator : public boost::iterator_facade< PassIterator, Pass, boost::forward_traversal_tag > { public: PassIterator(); PassIterator( Effect const& effect ); private: void increment(); Pass& dereference() const; Pass m_pass; friend class boost::iterator_core_access; }; Note how my Pass object is stored by-value in my PassIterator class. When I attempt to compile this class, it fails because dereference() is const and it is trying to return a reference to a const member. However, if I make dereference() non-const, it still fails because the base class is calling into PassIterator::dereference() through a const member function as well, so dereference() *must* be const in order to be callable by boost. How can I overcome this issue? const_cast? mutable? Thanks.

3 5

[EnableIf?] Seeking an example....
by Robert Jones 17 Sep '08

17 Sep '08

Somewhere in the Boost headers, or maybe the Boost documentation I have seen a bit of code which uses SFINAE, and also possibly the enable_if header to select either a find class method or find global template depending on what's available. It might have been written by Eric. I can't find it now,maybe it's not there any more, but if anyone can point me to it I'd really appreciate it! Thanks in advance, - Rob.

3 2

Tuples: Can someone help me generalize this?
by Derrick Hathaway 17 Sep '08

17 Sep '08

Hello, boost-users, what I am trying to accomplish is a generic collection of N objects of type Type. I need for the N objects to be tightly packed and I would like the collection to be constructible in this way: uniform_vector<3, float> my_point(1.0f, 2.1f, 3.2f); I'm very new to the template (meta)programming scene and I would like to get better at it, so any advice you could give that would be instructive in that regard would be much appreciated. The code below is what I have come up with. Question 1: Am I reinventing the wheel at all? In other words is there something I can just typedef to get this functionality? Question 2: If not, how could I generalize this? Is there a template metaprogramming way? I'm sure it can be done with the preprocessor but I'm no good with macros... but then again I'm not much good with templates either at least not by a boost mailing list standard anyway. :) Thanks, Derrick. // -- uniform_vector.hpp ------------------------------------------------------------------------ #ifndef DJH_UNIFORM_VECTOR_HPP #define DJH_UNIFORM_VECTOR_HPP #include <boost/tuple/tuple.hpp> namespace djh { template <unsigned int N, class Type> struct uniform_vector; template <class Type> struct uniform_vector<0, Type>; template <class Type> struct uniform_vector<1, Type> { static const unsigned int size = 1; typedef boost::tuple<Type> type; }; template <class Type> struct uniform_vector<2, Type> { static const unsigned int size = 2; typedef boost::tuple<Type, Type> type; }; template <class Type> struct uniform_vector<3, Type> { static const unsigned int size = 3; typedef boost::tuple<Type, Type, Type> type; }; template <class Type> struct uniform_vector<4, Type> { static const unsigned int size = 4; typedef boost::tuple<Type, Type, Type, Type> type; }; } #endif

2 3