April 2009 - Boost-users - lists.preview.boost.org

add_const_ref type transformation metafct
by Hicham Mouline 04 Apr '09

04 Apr '09

Hello, I wish to have a metafct that adds "const &" to types that have it or don't have it... template< typename T > struct add_const_ref { typedef typename boost::remove_const<T>::type t1; typedef typename boost::add_const<t1>::type t2; typedef typename boost::add_reference<t2>::type type; }; Does this exist already in type traits or elsewhere? I couldn't find.... Can this be improved in terms of reducing the number of tmpl instantiations? Note : add_const_ref< const double& >::type is const double& for e.g. Rds,

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issue using expat 2.0.1 with boost
by Sean Farrow 04 Apr '09

04 Apr '09

Hi: I am having an issue when trying to utilize the graphml library with the expat 2.0.1 library. The library fails to compaile saying it carn't find expat.h. My expat_include variable is set to: "c:\program files\expat\source\lib" and my expat_libpath is set to: "c:\program files\expat\bin\" Any help appreciated. Cheers Sean.

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Re: [Boost-users] boost::transform_iterator, boost::array::iterator and category
by Hicham Mouline 04 Apr '09

04 Apr '09

>Try returning a reference const double& instead of double. >struct UnaryFunction { > typedef const double& result_type; > const double& operator()( const pair<double, double>& e ) const > { > return e.first; > } >}; >Random access iterators must return an lvalue. >In Christ, >Steven Watanabe Thank you, the transformed iterator's category now matches std::random_access_iterator_tag. So in general, if I am passed a iterator (regardless whether it has been transformed by transform_iterator<> or not), the most generic test for random access category in C++03 __is__ against std::random_access_iterator_tag, __not__ against boost::random_access_traversal_tag. The latter is some implementation detail for the Boost.Iterator library, right? Thanks again,

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Thread safe intrusive ptr
by Jared Lee Richardson 04 Apr '09

04 Apr '09

I'm in the process of changing some of my shared_ptr's to intrusive_ptr's, and I'm trying to see how difficult it will be to make it thread-safe. I need intrusive_ptr's mostly due to size constraints(allocating an extremely large number of small objects), and also the ThisPtr issue. I tried to search and find any information about making them thread-safe, but what I found didn't explain the solution or the issues. What are the considerations for making intrusive_ptr thread safe? Is it as simple as a mutex-lock / atomic counter variable? Thanks, Jared

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Re: [Boost-users] Help using math functions
by Mario Chacon 04 Apr '09

04 Apr '09

Great!... This physics engine it's amazing!! I'm doing my first examples and works excellent! Thank you so much for your recommendation!! salu2... masch... On Fri, Apr 3, 2009 at 3:04 PM, Hostile Fork <hostilefork(a)gmail.com> wrote: > I doubt boost::math is high level enough for what you want to do. > > You probably want a physics engine. > http://en.wikipedia.org/wiki/Physics_engine > Haven't used any so I don't know which is best in the C++ world. But > there's at least one popular free one: Box2D > > http://cplus.about.com/b/2007/11/19/box-2d-online-c-physics-engine-demo.htm > > On Apr 3, 2009, at 9:35 AM, Mario Chacon wrote: > > Hello: > First at all I do not know about math, but I need to do some animations. I > need to simulate a movement of a ball into a pipe. I have all the interface > working, but now I have to do the best way to give it life..:D. My fists > steps was giving X,Y coordinates but I do not like this way, so I need some > tips to make it more professional way. How can I use boost math functions to > make it? > > Thank you.. > masch... > ** > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users > > >

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[Proto] lazy transform is not working
by Dave Jenkins 03 Apr '09

03 Apr '09

In the program below, I expected the proto::lazy transform to call the times2() function, but it doesn't. It does work correctly if you substitute times2<int> for proto::_state. Is this a bug or am I forgetting something? Thanks, Dave Jenkins #include <iostream> #include <boost/proto/proto.hpp> #include <boost/proto/transform.hpp> namespace proto = boost::proto; template<typename T, typename Callable = proto::callable> struct times2 { typedef T result_type; T operator()(T i) const { std::cout << "Called times2()\n"; return i * 2; } }; struct IntTimes2 : proto::when< proto::terminal<proto::_> , proto::lazy<proto::_state(proto::_value) > //, proto::lazy<times2<int>(proto::_value) > > {}; int main() { int dummy = 0; proto::terminal<int>::type i = {1}; IntTimes2()(i, times2<int>(), dummy); }

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boost::transform_iterator, boost::array::iterator and category
by Hicham Mouline 03 Apr '09

03 Apr '09

Hello, I have boost::array< pair<double, double>, 16 >::iterator (it has iterator_traits<>::iterator_category random_access_iterator_tag) which I have transformed with typedef transform_iterator< UnaryFunction, ... > iteratorIntoFirst; struct UnaryFunction: public std::unary_function< pair<double, double>, double> { double operator()( const pair<double, double>& e ) const { return e.first; } } However on asserting the category is still random access, boost static assert fails: BOOST_STATIC_ASSERT(( boost::is_convertible< iteratorIntoFirst, std::random_access_iterator_tag >::value )); >From the docs http://www.boost.org/doc/libs/1_38_0/libs/iterator/doc/transform_iterator.ht ml If Iterator models Readable Lvalue Iterator and if Iterator models "Random Access Traversal Iterator", then iterator_category is convertible to random_access_iterator_tag. Any ideas, Regards,

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[serialization] Multiply defined symbol: guid_initializer
by Robert Dailey 03 Apr '09

03 Apr '09

Hi, I'm currently trying to polymorphically serialize a class without using RTTI. I'm doing this currently in a file called StaticText.hpp: #ifndef RS_GUI_WIDGETS_STATICTEXT_HPP #define RS_GUI_WIDGETS_STATICTEXT_HPP #include <boost/scoped_ptr.hpp> #include <boost/serialization/access.hpp> #include <boost/serialization/base_object.hpp> #include <boost/serialization/string.hpp> #include <boost/serialization/extended_type_info_no_rtti.hpp> #include <boost/serialization/export.hpp> #include <rs/gui/widgets/Widget.hpp> #include <rs/gui/Text.hpp> namespace rs { class StaticText : public Widget { public: StaticText( std::string const& text ); void Update(); void Render( RenderSystem& renderer, Camera& camera ); char const* get_key() const; private: StaticText() {} template< class Archive > void serialize( Archive& archive, unsigned int version ) { archive & boost::serialization::base_object<Widget>( *this ); std::string text; archive & text; m_text.reset( new Text( text ) ); } boost::scoped_ptr<Text> m_text; friend class boost::serialization::access; }; } BOOST_CLASS_TYPE_INFO( rs::StaticText, extended_type_info_no_rtti<rs::StaticText> ) BOOST_CLASS_EXPORT( rs::StaticText ) #endif // RS_GUI_WIDGETS_STATICTEXT_HPP When I compile this into a LIB first, and then link the lib into an EXE, the linker says this (Visual Studio 2008): *gui.lib(StaticText.obj) : error LNK2005: "public: static struct boost::archive::detail::guid_initializer<class rs::StaticText> const & const boost::archive::detail::init_guid<class rs::StaticText>::guid_initializer" (?guid_initializer@?$init_guid@VStaticText@rs@@@detail@archive@boost@ @2ABU?$guid_initializer@VStaticText@rs@@@234@B) already defined in main.obj* * * If I move the 2 macro calls into the StaticText.cpp file, everything compiles/links just fine but I end up getting an exception thrown at runtime that says "unregistered void cast".

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[ASIO] Windows native type for ASIO serial port?
by Jeff Diewald 03 Apr '09

03 Apr '09

I have a boost::asio::serial_port object. What is the specific Windows type returned by native()? I'm having trouble with my serial communication across the serial port, and want to get more diagnostic information by going to the native level. The serial port hangs occasionally on a synchronous read_some call, and I haven't been able to figure out why. Ideally, I'd like to build a timeout into the synchronous call. Any help is appreciated, Jeff Diewald JEOL USA

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Re: [Boost-users] boost::transform_iterator, boost::array::iterator and category
by Hicham Mouline 03 Apr '09

03 Apr '09

>Hello >Following my previous post, >the transformed iterator has input iterator tag (not forward, not bidir, not random) >BOOST_STATIC_ASSERT(( > boost::is_convertible< > iteratorIntoFirst, > std::input_iterator_tag >>::value )); >But it should be random_access... Is there anything extra I need to put in the Unary fct of >transform_iterator? >Rds, There seems to be some boost::random_access_traversal_tag, and the static assert works with this tag??? Why isn't boost::random_access_traversal_tag equivalent to std::random_access_iterator_tag ? Rds,

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