Insert into an unordered boost bimap using TBB

I am very much confused with respect to TBB. I am trying to insert <key, value> pair in an unordered bimap, where the key is of type uint64_t and value is of type string. I made an attempt to create the loop object, which is in TBB.h file, and looks like

void ParallelIndex(uint64_t &kmer_len, std::string &split_kmer, std::string &sequence_content,
            uint64_t &sequence_length, size_t &kmer_position ) {
        parallel_for( blocked_range<size_t>(0, sequence_length),
                [&](const blocked_range<size_t>& r) {
            for(i = r.begin(); i < r.end();  ++i ){
                split_kmer = sequence_content.substr(i, kmer_len);
                reference_index_vector.insert(position(kmer_position, split_kmer)); 
                i += kmer_len-1;
                kmer_position += kmer_len;

                }
        }
        );
    }

and in the main function, which is in TBB.cpp, I tried to invoke the function

index.ParallelIndex(index.kmer_len, index.split_kmer, index.sequence_content,
        index.sequence_length, index.kmer_position );

It starts with 0 and goes through n. I am trying to increment i by 5 (first ++i and i +=kmer_len-1, like i = 0, 5, 10, 15, ... till n), but i gets incremented by only 1.

Complete code is shown below:

TBB.cpp

#include <iostream>
#include <string>
#include <algorithm>
#include <boost/bimap.hpp>
#include <boost/bimap/unordered_set_of.hpp>
#include <boost/bimap/unordered_multiset_of.hpp>
#include "tbb/parallel_for.h"
#include "TBB.h"
#include "tbb/tbb.h"
#include <tbb/blocked_range.h>



using namespace tbb;


namespace bimaps = boost::bimaps;
typedef boost::bimap<bimaps::unordered_set_of<uint64_t>,
        bimaps::unordered_multiset_of<std::string> > bimap_reference;
typedef bimap_reference::value_type position;
bimap_reference reference_index_vector;



uint64_t thread_test::create_index::kmer_len = 5;
std::string thread_test::create_index::split_kmer = "";
std::string thread_test::create_index::sequence_content = "ABCDDBACDDDCBBAAACBDAADCBDAAADCBDADADACBDDCBBBCDCBCDAADCBBCDAAAD";
uint64_t thread_test::create_index::sequence_length = 0;
size_t thread_test::create_index::kmer_position = 0;
size_t thread_test::create_index::i = 0;
int main(){
    thread_test::create_index index;
    index.sequence_length = index.sequence_content.length();

    index.ParallelIndex(index.kmer_len, index.split_kmer, index.sequence_content,
            index.sequence_length, index.kmer_position );

    for( bimap_reference::const_iterator iter = reference_index_vector.begin(), iend = reference_index_vector.end();
                iter != iend; ++iter ) {
            std::cout << iter->left << " <--> "<< iter->right <<std::endl;
        }

}

TBB.h

#ifndef TBB_H_
#define TBB_H_

#include<iostream>
#include <algorithm>
#include <utility>
#include <boost/bimap.hpp>
#include <boost/bimap/unordered_set_of.hpp>
#include <boost/bimap/unordered_multiset_of.hpp>
#include "tbb/tbb.h"
#include <tbb/parallel_for.h>
#include <tbb/blocked_range.h>
#include <tbb/mutex.h>


using namespace tbb;


namespace bimaps = boost::bimaps;

typedef boost::bimap<bimaps::unordered_set_of<uint64_t>,
        bimaps::unordered_multiset_of<std::string > > bimap_reference;
typedef bimap_reference::value_type position;
extern bimap_reference reference_index_vector;



namespace thread_test{

class create_index{

public:
    static uint64_t kmer_len;
    static std::string split_kmer;
    static std::string sequence_content;
    static uint64_t sequence_length;
    static size_t kmer_position;
    static size_t i;

//  using lambda function

    void ParallelIndex(uint64_t &kmer_len, std::string &split_kmer, std::string &sequence_content,
            uint64_t &sequence_length, size_t &kmer_position ) {
        parallel_for( blocked_range<size_t>(0, sequence_length),
                [&](const blocked_range<size_t>& r) {
            for(i = r.begin(); i < r.end();  ++i ){
                split_kmer = sequence_content.substr(i, kmer_len);
                reference_index_vector.insert(position(kmer_position, split_kmer));
                i += kmer_len-1;
                kmer_position += kmer_len;
                }
        }
        );
    }
};
}

#endif /* TBB_H_ */

problem is i gets incremented by 1 but I try to increment it by 5 as mentioned above.

Change for(i = r.begin(); i < r.end(); ++i ) to for(; i < r.end(); ++i ). In the first case you are reinitializing i = r.begin().