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I'm new to stackoverflow, sorry if I format the text wrong.

I have a polygon that I want to rotate by a given angle. 

void Polygon::rotateBy( const float cosx, const float sinx )
{
   for ( std::deque<PolygonPoint>::iterator i = point_list.begin(); i != point_list.end(); ++i )
    {
        i->x = (i->x * cosx) - (i->y * sinx);
        i->y = (i->x * sinx) + (i->y * cosx);
    }
}

This has a very unexpected result:

polygon.rotateBy(ccosx, csinx);

std::priority_queue<Edge, std::vector<Edge>, comparePolySegmentsByY> segments;
for(std::deque<PolygonPoint>::const_iterator i = (polygon.point_list.cbegin() + 1); i != polygon.point_list.cend(); ++i)
{
    segments.push(Edge(*(i-1), *i, i-1));
}
segments.push(Edge(polygon.point_list[ polygon.point_list.size() - 1 ], polygon.point_list[0], polygon.point_list.end() - 1));

The comparePolySegmentsByY:

   class comparePolySegmentsByY
   {
    public:
    bool operator()(const Edge& pol1, const Edge& pol2) const
    {
        float t1 = pol1.getMinY() - pol2.getMinY();
        if ( abs(t1) > Eps ) 
            return t1 > 0;
        else
        {
            if ( abs( pol1.getMinX() - pol2.getMinX() ) < Eps )
            {
                if ( abs ( pol1.getMaxY() - pol2.getMaxY() ) < Eps )
                    return pol1.getMaxX() > pol2.getMaxX();
                else
                    return pol1.getMaxY() > pol2.getMaxY();
            }
            else
                return pol1.getMaxX() > pol2.getMinX();
        }
    }
 };

I use the comparePolySegmentsByY to order those in the priority queue. This code gives back the error:

  Debug assertion failed: Invalid operator<

when I push the Edge in the segments priority list. If I comment out (delete) the rotate statement (but not the rotateBy function) all works fine! I really have no idea what is happening here.

Regic
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  • possible duplicate of [Invalid < operator assertion in sort](http://stackoverflow.com/questions/12549289/invalid-operator-assertion-in-sort); you need to make sure your sort function is stable. – Adam Maras Sep 03 '13 at 18:43
  • Wait I was wrong, Edge has no operator – Regic Sep 03 '13 at 18:54
  • Please post the code for `comparePolySegmentsByY`. – Adam Maras Sep 03 '13 at 18:58
  • New results: this problem doesn't occur with gcc on mac. I think it must be because of some optimalization that is done in visual c++ and that is incorrect. I think the iterator is the key somehow... the compiler handles it differently then simple pointers (f.e. debug assertions). I guess the makers of visual c++ compiler assume that you don't store iterator for an outside object (altho it is not forbidden as far as I know, iterator is just a kind of smart pointer). The moral is to avoid this I guess. – Regic Sep 04 '13 at 21:35

0 Answers0