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?

Quote:

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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?

Quote:

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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?

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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.