map_keys

map_keys example

Syntax	Code
Pipe	`rng \| boost::adaptors::map_keys`
Function	`boost::adaptors::keys(rng)`

Precondition: The value_type of the range is an instantiation of std::pair.
Postcondition: For all elements x in the returned range, x is the result of y.first where y is the corresponding element in the original range.
Range Category: Single Pass Range
Range Return Type: boost::select_first_range<decltype(rng)>
Returned Range Category: The range category of rng.

map_keys example

#include <boost/range/adaptor/map.hpp>
#include <boost/range/algorithm/copy.hpp>
#include <boost/assign.hpp>
#include <iterator>
#include <iostream>
#include <map>
#include <vector>

int main(int argc, const char* argv[])
{
    using namespace boost::assign;
    using namespace boost::adaptors;

    std::map<int,int> input;
    for (int i = 0; i < 10; ++i)
        input.insert(std::make_pair(i, i * 10));

    boost::copy(
        input | map_keys,
        std::ostream_iterator<int>(std::cout, ","));

    return 0;
}

This would produce the output:

0,1,2,3,4,5,6,7,8,9,