c++ - 子类模板错误(C++): "error: ' root' was not declared in this scope"

Question

我正在研究一个名为“BinarySearchTree”的子类，该子类继承自其父类(super class)“BinaryTree”

二叉树.h

template <class T>
class BinaryTree 
{

 public:
  BinaryTree() { root = NULL; }

 protected:
  BTNode<T> *root;  // Root node (NULL if the tree is empty)
};

二叉搜索树.h

template <class T>
class BinarySearchTree : public BinaryTree<T> 
{
 public:
  BinarySearchTree();  // call super's

  bool insert( const T& elem );
  bool insertHelper(BTNode<T> *&, T );
};

template<class T>
BinarySearchTree<T>::BinarySearchTree() :  BinaryTree<T>()
{
    root = NULL; // <---- error: In constructor 'BinarySearchTree<T>::BinarySearchTree()' 
                             //: BinarySearchTree.h:85: error: ‘root’ was not declared in this scope
};

我知道这与根在范围内未被识别有关，但我该如何解决这个问题？

Answer 1

例如:

BinaryTree<T>::root = NULL;

请看这里的解释:

http://www.parashift.com/c++-faq/nondependent-name-lookup-members.html