Re: [Boost-users] Newbie question on filter_iterators

On 9/13/05, Stephen Gross wrote:

Ok, I'm trying to learn the basics of filter_iterators. I've got a vector of ints. I want to iterate across the vector and print out every positive value in the vector. Currently, my code doesn't work because g++ doesn't like me assigning a vector::iterator to a filtered_iterator. Obviously, I've missed some crucial point on how the filtered_iterator is supposed to work. The example code in the boost library doesn't really address this specific use. Can someone show me how to make the code below work as intended?

Thanks in advance, --Steve

==== CODE FOLLOWS ====

struct is_positive { bool operator() (int i) { return i >= 0; } };

int main() { std::vector<int> i;

i.push_back(-5); i.push_back( 5); i.push_back(-4); i.push_back( 4); i.push_back(-3); i.push_back( 3); i.push_back(-2); i.push_back( 1);

typedef boost::filter_iterator filter_itr;

for(filter_itr f = i.begin(); f != i.end(); ++f) { std::cout << *f << std::endl; }

return 0; }

I think you'll need to use something like: for(filter_itr f(i.begin(), i.end()); f != filter_itr(i.end()); ++f) filter_iterator doesn't have an assignment operator, you have to go through the relevant constructor (see http://www.boost.org/libs/iterator/doc/filter_iterator.html#filter-iterator-...) Stuart Dootson