Boost.Range

Range Adaptors

`indexed`

rng | boost::adaptors::indexed

boost::make_indexed_range( rng )

Returns: A range adapted to return both the element and the associated index. The returned range consists of iterators that have in addition to the usual iterator member functions an index() member function that returns the appropriate index for the element in the sequence corresponding with the iterator.
Range Category: SinglePassRange

Example

        #include <boost/range/adaptor/indexed.hpp>
        #include <boost/range/algorithm/copy.hpp>
        #include <boost/assign.hpp>
        #include <algorithm>
        #include <iostream>
        #include <vector>
        
        template<class Iterator>
        void display_element_and_index(Iterator first, Iterator last)
        {
            for (Iterator it = first; it != last; ++it)
            {
                std::cout << "Element = " << *it
                          << " Index = " << it.index() << std::endl;
            }
        }
        
        template<class SinglePassRange>
        void display_element_and_index(const SinglePassRange& rng)
        {
            display_element_and_index(boost::begin(rng), boost::end(rng));
        }
        
        int main(int argc, const char* argv[])
        {
            using namespace boost::assign;
            using namespace boost::adaptors;
            
            std::vector<int> input;
            input += 10,20,30,40,50,60,70,80,90;
            
            display_element_and_index( input | indexed(0) );
            
            return 0;
        }

This produces the output:
Element = 10 Index = 0 Element = 20 Index = 1 Element = 30 Index = 2 Element = 40 Index = 3 Element = 50 Index = 4 Element = 60 Index = 5 Element = 70 Index = 6 Element = 80 Index = 7 Element = 90 Index = 8