fl_vertex.cxx lines 91 through 101 (exception was triggered by line 92):

void Fl_Graphics_Driver::transformed_vertex0(COORD_T x, COORD_T y) {
  
  if (!n || x != p[n-1].x || y != p[n-1].y) {
    
    if (n >= p_size) {
      
      p_size = p ? 2*p_size : 16;
      
      p = (XPOINT*)realloc((void*)p, p_size*sizeof(*p));
    
    }
    
    p[n].x = x;
    
    p[n].y = y;
    
    n++;
  
  }

}

Message about unhandled exception given by the debugger:

Unhandled exception at 0x009E1B19 in chapter13ex2.exe: 0xC000041D: An unhandled exception was 
encountered during a user callback.