I am working on a CAD software addon and i needed a solution, where you have to know if a point is inside a polygon or not. I have found some good solutions here (link), but none of them worked, when the polygon had holes in it! I figured it out so i want to share the code if somebody would need it.

struct Point2D
{
    double x;
    double y;
};

struct PolygonData
{
    std::vector<Point2D> coords;
    int nSubPolys;
    std::vector<int> pends;
};

bool IsPointInsidePolygon(const Point2D& p, const PolygonData& polygonData)
{
    double minX = 0.0;
    double maxX = 0.0;
    double minY = 0.0;
    double maxY = 0.0;

    for (int i = 0; i < polygonData.pends[1]; i++)
    {
        minX = std::min(polygonData.coords[i].x, minX);
        maxX = std::max(polygonData.coords[i].x, maxX);
        minY = std::min(polygonData.coords[i].y, minY);
        maxY = std::max(polygonData.coords[i].y, maxY);
    }

    if (p.x <  minX || p.x > maxX || p.y <  minY || p.y > maxY)
        return false;

    // check main polygon
    bool inside = false;
    for (int i = 0, j = polygonData.pends[0] - 1; i < polygonData.pends[0]; j = i++)
    {
        if ((polygonData.coords[i].y > p.y) != (polygonData.coords[j].y > p.y) &&
            p.x < (polygonData.coords[j].x - polygonData.coords[i].x) * (p.y - polygonData.coords[i].y) /
            (polygonData.coords[j].y - polygonData.coords[i].y) + polygonData.coords[i].x)
        {
            inside = !inside;
        }
    }

    // check subpolygons too if point is inside main polygon
    bool subInside = false;
    if (inside == true && polygonData.nSubPolys > 1)
    {
        int ind = 0;
        int prevPolySize = polygonData.pends[0];
        int actPolySize = 0;

        // skip 1st, because its the main polygon himself
        for (int ii = 2; ii <= polygonData.nSubPolys; ii++)
        {
            std::vector<API_Coord> actPolyCoords;
            ind = 0;

            actPolySize = polygonData.pends[ii] - polygonData.pends[ii - 1];
            std::vector<int>    pends;
            pends.push_back(actPolySize);

            for (int jj = prevPolySize; jj < polygonData.pends[ii - 1]; jj++)
            {
                Point2D actCoord;
                actCoords.x = polygonData.coords[jj].x;
                actCoords.y = polygonData.coords[jj].y;

                actPolyCoords.push_back(actCoord);
                ind++;
            }
            prevPolySize += ind;

            if (IsPointInsidePolygon(p, actPolyCoords)) // this is the function with the "old method" (not checking subpolygons)
                subInside = true;
        }

        if (subInside)
            inside = false;
    }

    return inside;
}   // IsPontInsidePolygon()

Have tested it and it works for me.

Note: i switched the code back from my API environment to STL, differences may occur.