August 2009 - Boost-users - lists.boost.org

Advise sought for container type
by Archie14 31 Aug '09

31 Aug '09

given the class like the one below: template <typename T> class animal { public: animal (const char* ofname) : _name(ofname) {} private: typedef T _T; std::string _name; _T behavior; } class MeatEater {}; class GrassEather {}; animal<MeatEater> bear ("bear"); animal<GrassEater> rabbit ("rabbit"); How to store "bear" and "rabbit" instances in a vector? Advise is greatly appreciated.

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Chain of Responsibility Pattern in a boost library
by Ryan McConnehey 30 Aug '09

30 Aug '09

Is there a boost library that implements the Chain of Responsibility Pattern? Ryan

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[mapreduce] Prim Calculator
by Christian Henning 30 Aug '09

30 Aug '09

Hi there, first of all, I'm not sure if boost user list should be used for boost-sandbox libraries. Anyone? Now, I would like create a new example for the mapreduce lib. How can I, for instance, setup a system that computes the prim numbers for 0 to 1,000,000,000. For this, I need to create the input for the map function on the fly, rather than reading some files from the hard drive. How is that possible? The documentation is a bit spare so far. Thanks, Christian

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[proto] folding a proto tree in reverse
by Maurizio Vitale 30 Aug '09

30 Aug '09

I need to traverse a proto tree from right to left so that given the statement: (a, b, c) = expr; I can assign in order c then b and lastly a. A fragment that does the order a,b,c (and work, but not very efficiently, which is why I want to go the other way) is: template<typename E> struct assign_aux { assign_aux (const E& rhs) : m_rhs (rhs) {} typedef int result_type; template<typename T> int operator()(const T& t, int offset) const { int next_offset = offset - actual_width_transform () (t); int value = systemc_eval (m_rhs.range (offset,next_offset+1)); const_cast<T&>(t) = value; return next_offset; } const E& m_rhs; }; template <typename E> struct assign<E, proto::tag::comma> { template<typename RHS> const E& doit (const E& e, const RHS& rhs) { int width = actual_width_transform () (e); fusion::fold(proto::flatten (const_cast<systemc_expression&>(e)), width-1, assign_aux<RHS> (rhs)); return e; } }; template<typename E> const systemc_expression& operator = (const E& e) const { BOOST_MPL_ASSERT ((proto::matches<systemc_expression, lhs_systemc_grammar>)); return assign<systemc_expression>().doit (*this, e); return *this; } I've tried to use fusion::reverse_view to invert the fusion sequence, but failed. I also suspect that the resulting code wouldn't be as good as it could be, which in my application is critical. So I looked at alternatives and tried proto::reverse_fold_tree. Here's my attempt: struct assign_terminal : proto::callable { typedef int result_type; template<typename T, typename O, typename R> int operator () (T& t, O o, const R& r) const { int width = actual_width_transform () (t); const_cast<T&>(t) = r.range (1,0); return o+width; } }; template <typename E> struct assign<E, proto::tag::comma> { template<typename RHS> const E& doit (const E& e, const RHS& rhs) { proto::reverse_fold_tree<_, int() , assign_terminal (_, proto::_state, proto::_data)>() (e, rhs); return e; } }; template<typename E> const systemc_expression& operator = (const E& e) const { BOOST_MPL_ASSERT ((proto::matches<systemc_expression, lhs_systemc_grammar>)); return assign<systemc_expression>().doit (*this, e); return *this; } But this doesn't seem to pass the data (rhs) to assign_terminal::operator () (expr, state, data). There're really very few examples on how to use proto::fold_tree and even fewer using the data parameter, so I don't have much to go on. Would anybody whose name is Eric tell me why I'm this stupid? TIA, Maurizio

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boost::multi_index_container vector-like O(1) time indexing question
by zap.foster 30 Aug '09

30 Aug '09

I originally posted this to the wrong group, but I intended it for this group. I have a boost::multi_index question. My current container has looked like the following for a very long time: typedef std::map<double,int> mtype_t; What I am looking for is a way to index the mtype_t::value_type.first value so that, syntactically, it appears like a vector. For example, the container I need would let me do something like: { container_t c; c.insert( container_t::value_type( keycount_t( 1.414,88) )); c.insert( container_t::value_type( keycount_t( 3.141,77) )); c.insert( container_t::value_type( keycount_t( 23.000,99) )); for(int index=0; index<c.size(); ++index) printf("%d\n",c[index].second); } You can see that I want to be able to index into the container much like one would do with a vector. But I want my indexing to be O(1) and not O(n). Now I still need to be able to iterate the container, and I need to be able to do efficient insertions, and yes, the contents of the container will get bigger and smaller and the values vary quite a lot. A basic sketch of the multi_index container (but without the vector-like index) would be: typedef struct { double key; int count; } keycount_t; struct by_key{}; typedef boost::multi_index_container< keycount_t, boost::multi_index::indexed_by < boost::multi_index::ordered_unique < boost::multi_index::tag<by_key>, boost::multi_index::member< keycount_t,double,&keycount_t::key > > > > container_t; This gives me the basics. But I cannot think of a way to add a secondary index that would give me the O(1) vector-like indexing. A use-case of the grammar I am after would be something like the following: void useless_function(container_t& c) { for(container_t::iterator i = c.begin(); i!=c.end(); ++i) print("key=%f\tval=%d\n",i->first,i->second); for(index=0; index<c.size(); ++index) print("key=%f\tval=%d\n",c[index].first,c[index].>second); } Here's WHY I need this: I have a stream of floating point values coming in (fixed to 5 significant digits). I need to keep count of how often any one of the floating point values is repeated. Very often I need to respond to requests as to the contents of the container at the Nth position. The slow O(n) method would be: const keycount_t& get_nth_record(int index,const container_t& c) { container_t::const_iterator i; for(i=c.begin(); i!=c.end(); ++i) if(--index==0 ) break; return( *i ); } But again, I need O(1) time, so I need some sort of index added to my container_t. Has anyone done this sort of thing before, and met the O(1) positional index requirement? Many thanks! -zap

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Intercommunicators with Boost.MPI ?
by Ashika Umanga Umagiliya 30 Aug '09

30 Aug '09

Greeting all, I am completly new to Boost and this is my very first post here . I have used Boost.Serialization and Boost.MPI to send user-defined-datatypes across MPI processes. (I use OpenMPI 1.3.3 ) Now, I want to spawn processes (MPI_Comm_spawn) and send across these objects among newly created child processes. How can I handle Intercommunicators with Boost.MPI ? Thanks in advance, umanga

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circular_buffer: How to make push_back() increase capacity?
by Robert Dailey 30 Aug '09

30 Aug '09

Hello, I have a list of colors that I need to be able to cycle through, either by rotating the container or by using an iterator that will rotate (i.e. return to the beginning when I increment at the end, and vice-versa). The goal is to be able to iterate through the container in a circular way and process all of the colors repeatedly. I chose a boost::circular_buffer for this job, I assumed it was the perfect tool for the job. It works great, except I would like to be able to call push_back() to add all of my colors to the buffer without having to call set_capacity() on it first. It's a minor thing, but omitting the call to set_capacity() would make it slightly more scalable/manageable since I won't have to keep incrementing the size of the capacity each time I want to add colors to the buffer. How can I achieve this? --------- Robert Dailey

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[boost-users][Variant] Sequence instantiation
by Ryan McConnehey 30 Aug '09

30 Aug '09

I have a sequence of types defined with the Loki library. I believe the equivalent would be boost::mpl::vector. The sequence is used to cause compile time asserts for unsupported types being passed to template functions. Boost variant can be created with a given list of types. typedef boost::variant< int, std::string, short, long > type_list; | <boost/variant.html>| Is it possible to create a variant from a sequence by either passing the sequence or iterating through each value in the sequence? This would reduce the code duplication of having one sequence for assert checking and the other for variants. Ryan

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Using BGL::read_graphml()
by Ramapriya Rangachar 30 Aug '09

30 Aug '09

Hello Boost users, I have managed to build the latest version (1.40.0) under Windows/MSVC. Could someone kindly point me to a working example that complements the link below, for read_graphml()? http://www.boost.org/doc/libs/1_40_0/libs/graph/doc/write_graphml.html Best regards, Ram _________________________________________________________________ Windows Live: Make it easier for your friends to see what you’re up to on Facebook. http://windowslive.com/Campaign/SocialNetworking?ocid=PID23285::T:WLMTAGL:O…

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[asio] DTR serial port option?
by Robert Dailey 30 Aug '09

30 Aug '09

Hello, I'm rewriting a C# program in C++. This C# program previously was communicating with a device via serial port. One thing in particular it was doing was setting the DTR flag to enabled. The MSDN article on this option is here: http://msdn.microsoft.com/en-us/library/system.io.ports.serialport.dtrenabl… <http://msdn.microsoft.com/en-us/library/system.io.ports.serialport.dtrenabl…>I do not see an option in the Boost.Asio documentation that is identical to this C# option. Can anyone comment on this? How can I enable DTR through Boost Asio's serial_port? --------- Robert Dailey

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