Boost C++ Libraries Home Libraries People FAQ More

PrevUpHomeNext
indexed
indexed example

Syntax

Code

Pipe

rng | boost::adaptors::indexed()

Pipe

rng | boost::adaptors::indexed(start_index)

Function

boost::adaptors::index(rng)

Function

boost::adaptors::index(rng, start_index)

Description

The index within each returned boost::range::index_value is equal to start_index + the offset of the element from the beginning of the range. In the versions of the functions that omit start_index the starting index is taken to be 0.

boost::range::index_value<
    typename boost::range_reference<decltype(rng)>::type,
    typename boost::range_difference<decltype(rng)>::type
>

The synopsis of index_value is as follows:

template<class T, class Indexable=std::ptrdiff_t>
class index_value : public boost::tuple<Indexable, T>
{
public:

    typedef ...unspecified...       index_type;
    typedef ...unspecified...       const_index_type;

    typedef ...unspecified...       value_type;
    typedef ...unspecified...       const_value_type;

    // ...unspecified... constructors

    index_type index();
    const_index_type index() const;

    value_type value();
    const_value_type value() const;
};

#include <boost/range/adaptor/indexed.hpp>
#include <boost/assign.hpp>
#include <iterator>
#include <iostream>
#include <vector>


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;

    for (const auto& element : input | indexed(0))
    {
        std::cout << "Element = " << element.value()
                  << " Index = " << element.index()
                  << std::endl;
    }

    return 0;
}

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


PrevUpHomeNext