How to use of "new" for polygons in C++ - c++

Question

The definitions of Circle and Polygon are here in Graph.h and graph.cpp.
For some exercise I need to have some unnamed shapes which are made using the new keyword. Both Circle and polygon are kinds of Shape.
For example if I have a vector_ref<Circle> vc; I can using this statement add an unnamed Circle into that vector: vc.push_back(new Circle (Point (p), 50)); because I can supply parameters (which are a point and a radius) of a circle when defining it.
But for polygons the subject is different.
For having a polygon I must declare it first, e.g., Polygon poly; then add points to it, this way, poly.add(Point(p));. Now it has caused a problem for me.
Consider I have a vector of polygons, Vector_ref<Polygon> vp; Now how to add (that is push back) a polygon using the new keyword just like I did for circle please?
My code is this:
#include <GUI.h>
using namespace Graph_lib;
//---------------------------------
class Math_shapes : public Window {
public:
Math_shapes(Point, int, int, const string&);
private:
//Widgets
Menu menu;
Button quit_button;
In_box x_coor;
In_box y_coor;
Vector_ref<Circle> vc;
Vector_ref<Graph_lib::Rectangle> vr;
Vector_ref<Graph_lib::Polygon> vt;
Vector_ref<Graph_lib::Polygon> vh;
//Action fucntions
void circle_pressed() {
int x = x_coor.get_int();
int y = y_coor.get_int();
vc.push_back(new Circle (Point(x,y), 50));
attach(vc[vc.size()-1]);
redraw();
}
void square_pressed() {
int x = x_coor.get_int();
int y = y_coor.get_int();
vr.push_back(new Graph_lib::Rectangle (Point(x,y), Point(x+100,y+100)));
attach(vr[vr.size()-1]);
redraw();
}
void triangle_pressed() {
int x = x_coor.get_int();
int y = y_coor.get_int();
vt.push_back(new Graph_lib::Polygon); // Problem is here!!
attach(vt[vt.size()-1]);
redraw();
}
void hexagon_pressed() {
int x = x_coor.get_int();
int y = y_coor.get_int();
Graph_lib::Polygon h;
h.add(Point(x,y)); h.add(Point(x+50,y+50)); h.add(Point(x+50,y+80));
h.add(Point(x,y+100)); h.add(Point(x-50,y+80)); h.add(Point(x-50,y+50));
vh.push_back(h);
attach(vh[vh.size()-1]);
redraw();
}
void quit() { hide(); }
// Call-back functions
static void cb_circle (Address, Address pw) { reference_to<Math_shapes>(pw).circle_pressed(); }
static void cb_square (Address, Address pw) { reference_to<Math_shapes>(pw).square_pressed(); }
static void cb_triangle (Address, Address pw) { reference_to<Math_shapes>(pw).triangle_pressed(); }
static void cb_hexagon (Address, Address pw) { reference_to<Math_shapes>(pw).hexagon_pressed(); }
static void cb_quit (Address, Address pw) { reference_to<Math_shapes>(pw).quit(); }
};
//----------------------------------------------------------------------------------
Math_shapes::Math_shapes(Point xy, int w, int h, const string& title):
Window(xy, w, h, title),
menu (Point(x_max()-150,70),120,30,Menu::vertical, "MathShapes"),
quit_button (Point(x_max()-100, 20), 70,20, "Quit", cb_quit),
x_coor(Point(x_max()-450,30),50,20,"x coordinate: "),
y_coor(Point(x_max()-250,30),50,20,"y coordinate: ")
{
attach(x_coor);
attach(y_coor);
attach(quit_button);
menu.attach(new Button(Point(0,0),0,0,"Circle",cb_circle));
menu.attach(new Button(Point(0,0),0,0,"Square",cb_square));
menu.attach(new Button(Point(0,0),0,0,"Equilateral triangle",cb_triangle));
menu.attach(new Button(Point(0,0),0,0,"Hexagon",cb_hexagon));
attach(menu);
}
//-------------------------------------------
int main()
try {
Math_shapes M_s(Point(100,100), 800, 600, "Math Shapes");
return gui_main();
}
catch(...)
{
return 0;
}

Answer 1

You simply need to hold a pointer to your polygon until you've put it in the conatiner:
Circle* pPoly = new Polygon();
// ...
pPoly->add(Point(p1));
// ...
pPoly->add(Point(p2));
// ...
vc.push_back(pPoly);
you probably want to use smart pointers rather than raw ones as above but this is where you can start.

Answer 2

Have you tried this
void triangle_pressed() {
int x = x_coor.get_int();
int y = y_coor.get_int();
Polygon *poly = new Polygon();
poly.add(Point(x));// add your points, I don't know if these are the right points
poly.add(Point(y));// but have you tried this way? creating it, adding, then calling
vt.push_back(poly); // push back without the move
attach(vt[vt.size()-1]);
redraw();

Answer 3

Well, in order to use the new operator, you would need to create a Polygon constructor that takes vector<Point> or initializer_list<Point> as an argument.
The other way around would be to create a helper function, e.g.
-- note that this is really suboptimal, there may be much better solution using move semantics, etc. (or even variadic template function for the matter)
Polygon* make_polygon(initializer_list<Point>& points)
{
Polygon* poly = new Polygon();
for (auto point : points)
poly->Add(point);
return poly;
}
And then just call vp.push_back(make_polygon({p1, p2, ...});
Obviously you could change the function to work without pointers simply by removing them alongside with the new operator call, but then it wouldn't work with your vector_ref<Polygon> type. You would need to use vector<Polygon> instead, as I assume that vector_ref<T> is just a typedef for vector<T*>