Rotating a polygon makes operator< disappear in visual c++ -

i'm new stackoverflow, sorry if format text wrong.

i have polygon want rotate given angle.

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

this has unexpected result:

polygon.rotateby(ccosx, csinx);  std::priority_queue<edge, std::vector<edge>, comparepolysegmentsbyy> segments; for(std::deque<polygonpoint>::const_iterator = (polygon.point_list.cbegin() + 1); != 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 comparepolysegmentsbyy order in priority queue. code gives error:

  debug assertion failed: invalid operator<  

when push edge in segments priority list. if comment out (delete) rotate statement (but not rotateby function) works fine! have no idea happening here.