Re: [Boost-users] any boost iterator adapter to make it java styleiterator ?

From: Jeff F (TriumphSprint2000_at_[hidden])
Date: 2007-03-02 09:29:56

abir basak wrote:
> Hi,
>   In some case I need a iterator which knows its position (index ) in
> the container, so that I can get the index back from iterator.
> The need is two fold.
> 1) This is needed for simultaneous traversal to different container.
>  i.e i have vector<point> and vector<velocity> where each point
> corresponds to velocity at same position. Thus converting the iterator
> to the index helps.

Since your dealing with random access iterators, std::distance( c.begin(), 
itr ) gives you that in constant time doesn't it, at least when you have 
access to the container.

>   But even better if I have a multi iterator, which can club a set of
> iterators, and allow to return all of them (like (*it).point() returns
> point, (*it).velocity() returns velocity etc. Also it defines ++, --
> etc the same way (i.e increments all these, or one in a logic , say
> next point is a jump in velocity by 2 etc), so that I can use
> boost::sub_range for these kind of iterator.

Doesn't http://www.boost.org/libs/iterator/doc/zip_iterator.html do what you 
want?

> 2) I need to convert iterator to index, as I need to store certain
> portion of a container (which changes its size) in a class. There I
> can only store index as iterator may get invalidated.
> It is something like,
>   void mark_if_useful(point_sub_range r){///an portion of the
>      container point_iterator it = r.begin();
>      for(; it != r.end() ; ++it){
>       if ((*it).x == 123 ) {
>           ///ok certain criterion is fulfilled
>           ///I need to mark (ans store tis position)

    std::size_t idx = std::distance( r.begin(), it );

>           ///I can't store *it as it is a pointer to a movable object
>           ///However I can store (*it).index() may be it is 5th
> location                in the vector, and (*it)>container() also the
> reference to the container
> ///may not be needed if the container is globally available.
> ///if some object also gets removed the the remove count from the
> container can be added to have a unique linear index (that can me done
> adding additional method to the container :) )
>       }
>      }
>   }

Jeff