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

From: abir basak (abirbasak_at_[hidden])
Date: 2007-02-19 09:50:46

shunsuke wrote:
>> 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<index_t,index_t> 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'.
> 
Here I am not getting the "index" from counting_iterator.
std::vector<int> v;
v+= 1,2,3,4,5,6,7,8,9,10;	
std::for_each(v.begin(),v.end(),std::cout<<_1<<" ");
counting_iterator<std::vector<int>::iterator > it_b =
                make_counting_iterator(v.begin()+3);
std::cout<<*it_b.base(); /// This prints the element at that pos i.e 4, 
not the position, i.e 3 . How to get the index back from iterator ?
>> 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
This one fits my need, thus I will replace my code by 
permutation_iterator.
>> 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/start_page.html
At present I don't need a polymorphic or heterogeneous iterator. I am 
looking at it.
And also looking at some iterator adapter (or range ) which can be 
stored inside a class or another container. i.e it will perform all of 
the operations using index & a reference to the container internally. 
Thus it needs to know the container & the position in the container. can 
  any_iterator or some other be stored (or boost::sub_range of those 
iterator adapter)  inside a class , or I need to store index and 
construct iterator with the help of container.
> 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
> 
This is ok. I will be happy to use it.
> 
> Finally, I've written everything noted above. :-)
> http://tinyurl.com/2o2mnv
> 
> 
Still looking at them. Will get an idea within a day.
> Regards,
> 
Thanks for specifying the links, and sorry for disturbing.

abir
-- 
Abir Basak, Member IEEE
B. Tech, IIT Kharagpur
email: abir_at_[hidden]
homepage: www.abirbasak.com