# Boost.Range

## Range Adaptors

#### `filtered`

>     rng | boost::adaptors::filtered( pred )

>     boost::make_filtered_range( rng, pred )

- Precondition: The value-type of the range is convertible to the argument type of `pred`.
- Postcondition: For all elements `x` in the returned range, `pred(x)` is `true`
- Throws: Whatever the copy-constructor of pred might throw.
- Range Category: ForwardRange
- Returned Range Category: ForwardRange

### Example

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

            struct is_even
            {
                bool operator()(int x) const { return x % 2 == 0; }
            };

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

                std::vector<int> input;
                input += 1,2,3,4,5,6,7,8,9;

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

                return 0;
            }

This would produce the output:
`2,4,6,8`

(C) Copyright Neil Groves 2009 (C) Copyright Thorsten Ottosen 2003-2004