Instantiation of variable but no definition is available

Question

I get linking error while compiling that code, and I have a warning from Xcode:

Instantiation of variable 'quickhull::QuickHull::Epsilon' required here, but no definition is available

And here is the definition of the function:

namespace quickhull {

    template<>
    const float QuickHull<float>::Epsilon = 0.0001f;

    template<>
    const double QuickHull<double>::Epsilon = 0.0000001;

    /*
     * Implementation of the algorithm
     */

    template<typename T>
    ConvexHull<T> QuickHull<T>::getConvexHull(const std::vector<Vector3<T>>& pointCloud, bool CCW, bool useOriginalIndices, T epsilon) {
        VertexDataSource<T> vertexDataSource(pointCloud);
        return getConvexHull(vertexDataSource,CCW,useOriginalIndices,epsilon);
    }




ConvexHull<FloatType> getConvexHull(const std::vector<Vector3<FloatType>>& pointCloud, bool CCW, bool useOriginalIndices, FloatType eps = Epsilon);




template<typename FloatType>
    class QuickHull {
        using vec3 = Vector3<FloatType>;

        static const FloatType Epsilon;

        ConvexHull<FloatType> getConvexHull(const VertexDataSource<FloatType>& pointCloud, bool CCW, bool useOriginalIndices, FloatType eps);
    public:
        // Computes convex hull for a given point cloud.
        // Params:
        //   pointCloud: a vector of of 3D points
        //   CCW: whether the output mesh triangles should have CCW orientation
        //   useOriginalIndices: should the output mesh use same vertex indices as the original point cloud. If this is false,
        //      then we generate a new vertex buffer which contains only the vertices that are part of the convex hull.
        //   eps: minimum distance to a plane to consider a point being on positive of it (for a point cloud with scale 1)
        ConvexHull<FloatType> getConvexHull(const std::vector<Vector3<FloatType>>& pointCloud, bool CCW, bool useOriginalIndices, FloatType eps = Epsilon);

}

The call

 QuickHull<float> qh; // Could be double as well


  hull = qh.getConvexHull(pointCloud, true, false);

Linking Error

  "quickhull::QuickHull<float>::Epsilon", referenced from:
   "quickhull::QuickHull<float>::getConvexHull(std::__1::vector<quickhull::Vector3<float>, std::__1::allocator<quickhull::Vector3<float> > > const&, bool, bool, float)", referenced from:

@MichaelWalz I have added part of the header file, its very large one — andre, Jan 12 '18 at 10:41
Have a look at this https://stackoverflow.com/questions/1553854/template-static-variable — Pumkko, Jan 12 '18 at 10:42
please note the "minimal" in [mcve]. You need to refactor your code to contain only what is needed to reproduce the error — 463035818_is_not_an_ai, Jan 12 '18 at 10:43
Also note the "complete". We really need a `main` function here so we can try to link. You should reduce this problem to a single file which compiles and fails with the link error. Try to make the file as simple as possible. For example, everything as struct not class; all member functions defined in the body of the struct. — Martin Bonner supports Monica, Jan 12 '18 at 10:47
@UKMonkey How would I define it outside the class while I need a template type for it ? — andre, Jan 12 '18 at 10:51
You're right - https://stackoverflow.com/questions/3229883/static-member-initialization-in-a-class-template or the one raised by pumkko is much closer to the mark — UKMonkey, Jan 12 '18 at 10:56

score 1 · Accepted Answer · answered Jan 12 '18 at 11:08

Generally, when declaring a static data member in a class, you have to provide a variable definition "outside" the class definition, e.g.

class Test {
   public:
   static int g;
};
...
int Test::g = 0;

The same happens to classes "generated" through templates, and the notation is as follows:

template<typename FloatType>
class QuickHull {
    static const FloatType Epsilon;
}
...
template<typename FloatType >
QuickHull<FloatType>::Epsilon = 0.0;

Instantiation of variable but no definition is available

1 Answers1