ID 字段在自定义点类中间歇性丢失

The following code shows an example point class (int id is the identifier) and also a sample of code which compiles and runs (with appropriate #include and namespace declarations) however it keeps removing my point IDs:

点类:

class My_Point
{
public:

    My_Point(const My_Point &p);
    My_Point(double x = 0.0, double y = 0.0, int new_id = 0);

    const double Get_X() const;
    const double Get_Y() const;

    void Set_X(double new_x);
    void Set_Y(double new_y);

    const int Get_ID() const;
    void Set_ID(int new_id);

private:
    int id;
    double x;
    double y;
}

复制构造函数:

My_Point::My_Point(const My_Point &p) {
    Set_X(p.Get_X());
    Set_Y(p.Get_Y());
    Set_ID(p.Get_ID());
} 

测试代码:

void TestPolygon()
{
vector < My_Point > p;

p.push_back(My_Point(0.0, 0.0, 0));
p.push_back(My_Point(1.0, 0.0, 1));
p.push_back(My_Point(1.0, 1.0, 2));
p.push_back(My_Point(0.0, 1.0, 3));
p.push_back(My_Point(0.0, 0.0, 4));

cout << "Initial points are:
";

for (int i = 0, n = p.size(); i < n; i++)
{
    cout << point_to_string(p.at(i)) << "
";
}

detect_enter();

polygon<My_Point> poly;
append(poly, p);

//this code gives each point with an incorrect id of 0
cout << "Polygon points are:
";

for (int i = 0, n = poly.outer().size(); i < n; i++)
{
    cout << point_to_string(poly.outer().at(i)) << "
";
}

detect_enter();

strategy::transform::rotate_transformer<degree, double, 2, 2> rotate(45.0);

for (int i = 0, n = poly.outer().size(); i < n; i++)
{
    transform(poly.outer().at(i), poly.outer().at(i), rotate);
}

vector<My_Point> p2;
p2 = poly.outer();

//this code gives an incorrect id of 0.
cout << "Final points are:
";

for (int i = 0, n = p2.size(); i < n; i++)
{
    cout << point_to_string(p2.at(i)) << "
";
}

detect_enter();

//this code gives the correct id values as expected.
cout << "Original points were:
";

for (int i = 0, n = p.size(); i < n; i++)
{
    cout << point_to_string(p.at(i)) << "
";
}
}

推荐答案

正如 sehe 所指出的，库只知道如何访问 My_Point 的 X 和 Y 坐标.此外，rotate_transformer 只知道如何旋转点的几何部分，它不知道您正在存储 ID 并且您想复制它们.您可以尝试为此编写自己的策略.类似(未测试):

struct my_rotate_transformer
    : public strategy::transform::rotate_transformer<degree, double, 2, 2>
{
    typedef strategy::transform::rotate_transformer<degree, double, 2, 2> base_t;

    my_rotate_transformer(double angle)
        : base_t(angle)
    {}  

    template <typename P1, typename P2>
    bool apply(P1 const& p1, P2& p2) const
    {
        p2.Set_ID(p1.Get_ID());
        return base_t::apply(p1, p2);
    }
}

polygon<My_Point> poly_in;
polygon<My_Point> poly_out;
bg::transform(poly_in, poly_out, my_rotate_transformer(45))