Re: [Boost-users] any boost library for referring a portion of the container ?

abir basak wrote:

It is better if I try to post some code to show what I exactly trying to do. ( I am trying to capture digital pen input and create a hierarchical structure from it ) ///This is a range (2 point index, which can create 2 iterators with the ///help of the container, I am using boost::sub_range for that ) typedef std::pairstd::size_t,std::size_t range_t;

///This is a multi index range allows iterate over a few specific index ///on a container , used with my index_range and container. (for ///simplicity now it uses vector, it can be any container ) typedef std::vector index_t;

///The index range. iterates over the specific position on the container ///a simplified version to show the concept. It has const correctness ///and all other functions that sub_range has. It takes container & ///index vector unlike iterators in boost::sub_range. template<typename C> class index_range{ public: typedef C container_type; typedef typename C::iterator iterator; typedef typename C::reference reference; typedef typename C::pointer pointer; typedef typename C::size_type size_type; private: index_t index_; C& c_; size_type pos_; public: index_range(C& c,index_t index) : c_(c),index_(index) , pos_(0){} size_type size()const { return index_.size();} reference operator[](size_type pos) { return c_[ index_[pos] ] }; reference front() { return c_[index_[0] ] ;} reference back() { return c_[index_[size()-1]] ; } reference operator++(){ return c_[index_ [ pos_ ++] ] ; } }; ///The point comes as user input through digital pen struct point{ int x; int y; point(int _x,int _y) : x(_x),y(_y){} }; typedef std::deque<point> point_buffer; typedef boost::sub_range point_range;

///The buffer of points. point_buffer points;

///trace a continuous user writing, until pen up. points a portion ///of point_buffer struct trace{ range_t range; point_range get_points() { return boost::make_iterator_range(points.begin()+range.first,points.begin()+range.second); } };

typedef std::deque<trace> trace_buffer; typedef boost::sub_range trace_range; typedef index_range trace_index_range; ///buffer for traces. trace_buffer traces;

///a page contains a set of traces. struct page{ range_t range; trace_range get_traces(){ return boost::make_iterator_range(traces.begin()+range.first,traces.begin()+range.second); } };

///a word contains a few discrete traces, may not be continuous to ///represent by 2 index. But 2 word may not contain same trace. i.e ///common way of writing, but 2 or more character may contain same trace //(like cursive writing) struct word{ index_t index; trace_index_range get_traces(){ return index_range(traces,index); } }; A few additional things do happen, like each container keeps track of how many elements had been removed, to translate properly from index to iterator.

So there are 3 library I am searching, 1) Index -> iterator , and iterator -> index conversion (I know that 2 famous facts in STL that iterator doesn't know container and their position, but that is only applicable for pointers . There is no harm to know this facts from iterator. and thus some library can do to-from conversion between iterator & index position , or better sub_range & pair any library ?

Boost has 'counting_iterator'. http://www.boost.org/libs/iterator/doc/counting_iterator.html You can call 'counting_iterator::base()' if you want the 'index'.

2) a library like index_range, which hops over a container (random access preferably ) adding an user specified offset to the iterator position

Boost has 'permutation_iterator'. http://www.boost.org/libs/iterator/doc/permutation_iterator.html Unfortunately, 'boost::permutation_iterator' cannot work with 'boost::counting_iterator', hence requires a patch something like this.. http://tinyurl.com/35qkzw

3) an utility which allows to refer a portion (or some portions ) of a container to be stored ( i.e store by index & return by iterator ) inside another class , using the above two library ....

If you take the portions represented by different types into a single deque, Dr.Becker's 'any_iterator' is a candidate. http://thbecker.net/free_software_utilities/type_erasure_for_cpp_iterators/s... Well, you have to make a range by using these iterators, because Boost doesn't have the range wrappers yet. It would be something like this.. http://tinyurl.com/38474e Finally, I've written everything noted above. :-) http://tinyurl.com/2o2mnv Regards, -- Shunsuke Sogame