Is it possible (or ok) to have a std::list of std::list's?

Question

I have a std::list of Points (that simply store an x, y). Each one of these points represents a polygon, which I later draw.

class Point {
public:
    int x, y;
    Point(int x1, int y1)
    {
        x = x1;
        y = y1;
    }
};

std::list <Point> currentPolygon;

I would like to have a list of these polygons (lists themselves).

Is this possible? How do I have a std::list of a list of Points (so I can store more than one polygon).

Answer 1

It sure is. But what you probably want - for expandability purposes later - create a second class - "polygon", that holds a list of points. Then use a list of polygons.

EDIT: I'm no C++ programmer, so I'm sure an implementation like j_random_hacker's response is better if you're needing this for a real project. I merely wanted to give a quickie code example of this design.

class Point {
public:
    int x, y;
    Point(int x1, int y1)
    {
        x = x1;
        y = y1;
    }
};

class Polygon {
public:
    std::list <Point> currentPolygon;
    Polygon(std::list <Point> p1)
    {
        currentPolygon = p1
    }
};

Answer 2

You could use this:

std::list< std::list<Point> > polygons;

To make things easier, use typedefs.

class Point {
public:
    int x, y;
    Point(int x1, int y1)
    {
        x = x1;
        y = y1;
    }
};
typedef std::list<Point> PolygonType;
typedef std::list<PolygonType> PolygonsType;

Answer 3

Here is Jeffrey's code again, tidied up slightly to fix what I was whingeing about in the comments :)

class Point {
public:
    int x, y;
    Point(int x1, int y1) : x(x1), y(y1)
    {
    }
};

class Polygon {
public:
    std::list <Point> currentPolygon;    // Consider making this private.
    explicit Polygon(std::list <Point> const& p1) : currentPolygon(p1)
    {
    }
};

[EDIT: Thanks to Matt Davis for pointing out that the user-defined copy constructor I provided was unnecessary, which simplifies things.]