boost_1_45_0/libs/range/doc/reference/adaptors/indexed.qbk

[section:indexed indexed]

[table
    [[Syntax] [Code]]
    [[Pipe] [`rng | boost::adaptors::indexed`]]
    [[Function] [`boost::adaptors::index(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:] __single_pass_range__
* [*Returned Range Category:] The range category of `rng`

[section:indexed_example indexed 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));
}

template<class Iterator1, class Iterator2>
void check_element_and_index(
        Iterator1 test_first,
        Iterator1 test_last,
        Iterator2 reference_first,
        Iterator2 reference_last)
{
    BOOST_CHECK_EQUAL( std::distance(test_first, test_last),
                       std::distance(reference_first, reference_last) );

    int reference_index = 0;

    Iterator1 test_it = test_first;
    Iterator2 reference_it = reference_first;
    for (; test_it != test_last; ++test_it, ++reference_it, ++reference_index)
    {
        BOOST_CHECK_EQUAL( *test_it, *reference_it );
        BOOST_CHECK_EQUAL( test_it.index(), reference_index );
    }
}

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;
}
``
[endsect]

This would produce 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
``
[endsect]