c++ - 如何在 C++ 中将 "new"用于多边形

Question

Circle 的定义和 Polygon是here在 Graph.h 和 graph.cpp 中。

对于某些练习，我需要一些未命名的 shapes这是使用 new 制作的关键词。两者 Circle和 polygon是种Shape .

例如，如果我有一个 vector_ref<Circle> vc;我可以使用此语句添加一个未命名的 Circle进入该 vector :vc.push_back(new Circle (Point (p), 50));因为我可以提供 circle 的参数(点 和半径)定义它的时候。

但对于 polygons主题不同。因为有一个 polygon我必须先声明它，例如 Polygon poly;然后给它加点，这样，poly.add(Point(p)); .现在它给我带来了麻烦。

假设我有一个 polygons 的 vector , Vector_ref<Polygon> vp;现在如何添加(即推回)polygon使用 new关键字就像我为 circle 做的一样请？我的代码是这样的:

#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

您只需将指针指向您的多边形，直到将其放入容器中:

Circle* pPoly = new Polygon();
// ...
pPoly->add(Point(p1));
// ...
pPoly->add(Point(p2));
// ...
vc.push_back(pPoly);

您可能想使用智能指针而不是上面那样的原始指针，但这是您可以开始的地方。