Question

I have a vector of IntRect: vector.

How can I iterate from both ends of the list and stop the iterator when the iterator intersects?

vector<IntRect>::iterator itr = myVector.begin();
  vector<IntRect>::reverse_iterator revItr.rbegin();

  for (; /*check itr and revItr does not intersect, and itr and revItr do not end */ ; ++itr, ++revItr) {
    IntRect r1 = *itr;
    IntRect r2 = *revItr;

    // do something with r1 and r2

  }

Thank you.

Answer 1

if(!myVector.empty()) {
    for(vector<IntRect>::iterator forwards = myVector.begin(), 
                                  backwards = myVector.end()-1;
        forwards < backwards;
        ++forwards, --backwards) {

            // do stuff
    }
}

I think you need to check empty() with that implementation – suspect that end()-1 isn’t defined if the vector is empty. I haven’t used it before, but Dinkumware STL at least has operator < defined for vector iterators and it appears to do something sensible.

Also note that you need to check <, not just equality – that takes care of the (common) case where your vector has an even number of entries and the two iterators would step past one another.