Template class nested in template class

I'm trying to create a container class that has node-like objects. These need to be templates. I tried:

Code:

template <class T>
class H {
 private:
  template <class T> class K;
  //...
};

template <class T>
class H<T>::K {
 //...
};

But that doesn't work. I tried some random things in hopes that I'd get the combination right, but none of them worked.

What am I doing wrong? How do I fix this?

Thank you

You can't reuse "T" as a template parameter. How could the inner class possibly distinguish between the two? Name it something else.

I didn't want it to. The types always have to be the same. I guess this is achieved by having two separate variables anyways, though. Yes?

Originally Posted by yahn

I didn't want it to. The types always have to be the same. I guess this is achieved by having two separate variables anyways, though. Yes?

If the types have to be the same then the inner class does not need to be a template.

Oh, that makes sense. How about when you want to return the nested type?

I have:

Code:

template<class T>
class H {
 private:
  class K;
  // ...
};

Class K {
 // ...
 public:
  K *doSomething();
  // ...
};

template<class T>
H<T>::K *H<T>::K::doSomething() {
 // ...
};

That gives the error : "dependent name is not a type prefix with 'typename' to indicate a type"

Do you know what I'm doing wrong?

Thank you

That looks wrong. If K is nested in H, then I would expect you to define it as:

Code:

template<class T>
class H<T>::K {
public:
    K* doSomething();
};

though personally I would just define it within the definition of H. Anyway, once that is fixed, the next problem would be that in H<T>::K, the nested name K depends on the template parameter T. As such, it could, in theory, be interpreted not as a type name, but as an object name, and the rules say that it should be interpreted as a non-type name by default. As such, you should change to:

Code:

template<class T>
typename H<T>::K* H<T>::K::doSomething() {
    // ...
}

Sorry, I had properly declared the class, I just didn't write it done correctly when making the example. But, you're suggested works. Thank you

Now, I'm not getting any errors about the class, but when trying to compile I am getting unresolved external symbols to the functions of the class. What does that mean?

Originally Posted by yahn

Now, I'm not getting any errors about the class, but when trying to compile I am getting unresolved external symbols to the functions of the class. What does that mean?

My guess is that you tried to separate the implementation of the class template into a source file, as would normally be done for classes. However, with templates, you generally have to put everything in the header file.