C++: Trying to declare and define templated class within templated class. What is wrong with my code?

Question

#ifndef SIMPLE_BST_HPP
#define SIMPLE_BST_HPP

#include <vector>

template <class T>
class SimpleBST {

public:

    SimpleBST(std::vector<T>);


    template <class T>
    class BSTNode
    {


    };

};


#endif

However, I get this error when compiling:

In file included from SimpleBST.cpp:1:0:
SimpleBST.hpp:14:12: error: declaration of ‘class T’
  template <class T>
            ^
SimpleBST.hpp:6:11: error:  shadows template parm ‘class T’
 template <class T>
           ^
In file included from main.cpp:1:0:
SimpleBST.hpp:14:12: error: declaration of ‘class T’
  template <class T>
            ^
SimpleBST.hpp:6:11: error:  shadows template parm ‘class T’
 template <class T>
           ^

Does anyone know why I am unable to define the BSTNode? I will eventually make the node private, but at this point, I am just trying to declare a class within the SimpleBST that can be used as the basic node to store the elements of my binary search tree.

Thanks!

Answer 1

Considering the classes you are creating, it does not make sense that you are using a class template for the nested class.

You don't want SimpleBST<double> to contain BSTNode<int> .

Make BSTNode a simple nested type under SimpleBST<T> .

template <class T>
class SimpleBST {

public:

    SimpleBST(std::vector<T>);

    class BSTNode
    {
    };

};