FLTK, creating a rounded box

[abbassi]

Hi guys,

The problem says: Draw a box with rounded corners. Define a class Box, consisting of four lines and four arcs.
So I wrote the below code for that exercise:

#include <Simple_window.h>
Simple_window win(Point(100,100), 600,400, "semi-ellipse");

struct Box: Shape{

	Box(Point p, int ww, int hh): w(ww), h(hh) 
    	{ add(Point(p.x-ww,p.y-hh));  }

	void d_l() const        //creating 4 lines
     {
	    Line hrz1 (Point(150,100), Point(400,100));
	    Line hrz2 (Point(150,300), Point(400,300));
	    Line ver1 (Point(507,150), Point(507,250));
	    Line ver2 (Point(41,150), Point(41,250));

		win.attach(hrz1);
		win.attach(hrz2);
		win.attach(ver1);
		win.attach(ver2);
     }

	void draw_lines() const      //creating 4 arcs
	{
		fl_arc(point(0).x,point(0).y,w,h,30,90);
		fl_arc(point(0).x,point(0).y,w,h,270,330);
		fl_arc(point(0).x,point(0).y,w,h,90,150);
		fl_arc(point(0).x,point(0).y,w,h,210,270);
	}
	
private:
	int w;
	int h;
};

int main()
{
    using namespace Graph_lib; 
	
	Box b(Point(100,100),100,50);
	win.attach(b);
        win.wait_for_button();
}

When I ran it I faced this exception:

Unhandled exception at 0x757FE9D7 (ole32.dll) in test.exe: 0xC0000005: Access violation reading location 0x00000004.


I know this refers to declaring "Simple_window win(Point(100,100), 600,400, "semi-ellipse");" in global state. But I did that because I had to do it. The problem is that how to attach lines and also object (here b) to Simple_window win in either parts (main() function and also Box struct).