[Boost-users] Newbie question on filter_iterators

From: Stephen Gross (sgross_at_[hidden])
Date: 2005-09-13 09:49:57

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<is_positive, std::vector<int>::iterator> 
filter_itr;

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

  return 0;
}