Question

Graph.h 和 graph.cpp 中Circle和Polygon的定义为here。

对于某些练习，我需要使用shapes关键字创建一些未命名的new。 Circle和polygon都是Shape种。

例如，如果我有vector_ref<Circle> vc;我可以使用此语句在该向量中添加一个未命名的Circle：vc.push_back(new Circle (Point (p), 50));因为我可以提供参数（这是点<定义它时，{em>和半径）circle。

但对于polygons，主题是不同的。要获得polygon，我必须首先声明它，例如Polygon poly;，然后以这种方式poly.add(Point(p));添加点数。现在它给我带来了一个问题。

考虑我有polygons的向量，Vector_ref<Polygon> vp;现在如何添加（即推回）polygon使用new关键字就像我对circle所做的那样好吗？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

你需要握住指向多边形的指针，直到你把它放在conatiner中：

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

你可能想要使用智能指针而不是上面的原始指针，但这是你可以开始的地方。

Answer 2

你试过这个吗？

 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

好吧，为了使用new运算符，您需要创建一个以vector<Point>或initializer_list<Point>为参数的Polygon构造函数。

另一种方法是创建辅助函数，例如
- 请注意，这确实不是最理想的，使用移动语义等可能有更好的解决方案（甚至可变参数的模板函数）

Polygon* make_polygon(initializer_list<Point>& points)
{
    Polygon* poly = new Polygon();
    for (auto point : points)
        poly->Add(point);

    return poly;
}

然后只需致电vp.push_back(make_polygon({p1, p2, ...});

显然，您可以将功能更改为无指针，只需将其与新的操作员调用一起删除即可，但是它不会与您的vector_ref<Polygon>类型一起使用。您需要使用vector<Polygon>，因为我认为vector_ref<T>只是vector<T*>

的typedef

如何在C ++中使用“new”作为多边形

3 个答案: