Templated constructor, parenthesis expected

Question

I have a class template:

template <class T>
class NormalEstimator
{
    public:
        NormalEstimator(pcl::PointCloud<T>::Ptr cloud) : _cloud(cloud) {}

        void computeNormals();
        pcl::PointCloud<pcl::Normal>::Ptr getNormals();
    private:
        typename pcl::PointCloud<T>::Ptr _cloud;
        pcl::PointCloud<pcl::Normal>::Ptr _normals;

        int _kNeighbours;
};

The member functions are declared in the header file as well. When compiling, this gives me the error:

.../normal_estimator.h:12: error: expected ')' before 'cloud'

Am I forgetting something? Do I need to specify 'typename' on the constructor as well in some way or form?

See [Where and why do I have to put the “template” and “typename” keywords?](http://stackoverflow.com/q/610245/420683) — dyp, Mar 10 '14 at 14:44
`pcl::PointCloud::Ptr` is a dependant name because T is a template parameter. You have to write `typename pcl::PointCloud::Ptr`. — Simple, Mar 10 '14 at 14:45

score 1 · Answer 1 · answered Mar 10 '14 at 14:46

It's a dependent name. The type ::Ptr is dependent on T. So you have to use "typename" to tell the compiler that the value of ::Ptr is a type.

 NormalEstimator(typename pcl::PointCloud<T>::Ptr cloud)

This is because as long as T is defined the type of ::Ptr might be anything (a static member / type / static function).

http://en.cppreference.com/w/cpp/language/dependent_name

score 0 · Answer 2 · answered Mar 10 '14 at 14:44

0

Did you try this ?

NormalEstimator(typename pcl::PointCloud<T>::Ptr cloud) : _cloud(cloud) {}

answered Mar 10 '14 at 14:44

Caduchon

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score 0 · Accepted Answer · answered Mar 10 '14 at 14:45

0

Yes, you need typename in the constructor parameter as well because T is a dependent type:

NormalEstimator(typename pcl::PointCloud<T>::Ptr cloud)
//              ^^^^^^^^

answered Mar 10 '14 at 14:45

David G

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Thank you. I am going to read up on templates and dependent types. – Moos Hueting Mar 10 '14 at 14:47

Templated constructor, parenthesis expected

3 Answers3