如何使用 C++ 中的功能指针进行二叉搜索树？

Question

这是 BinarySearchTree.h 文件

I am creating a binary search tree template class, and want to use function pointers for the inorder traversal function, i am okay with function pointers but for some reason am lost on how to use the inorder once the code is in place. 网上没有太多其他东西对我有帮助，所以任何反馈都会很棒。

template <class T>
struct nodeType  
{
    // your write the code
        T data;
        nodeType * left;
        nodeType * right;
        nodeType(T key) :data(key), left(nullptr), right(nullptr) {}

};

template<class T>
typedef void (*f1Typ)(T &);  // you are not restricted to a single parameter. You 
                                // decide on how many parameters and provide rationale

template <class T>
class Bst // answer why class encapsulation is used - rationale
{

public:

            // you write whatever else is needed. You already have some from Lab 9.
            // insert is needed.

    void inOrderTraversal(f1Typ f1 ) const;
    
    void preOrderTraversal() const; // parameter f1 in here too. left as an exercise
    void postOrderTraversal() const; // parameter f1 in here too. left as an exercise

private:
    
    
    nodeType<T> *root;

            // you write the rest

    void inOrder(f1Typ f1, nodeType<T> *p) const;
    // you write whatever else is needed.


};

// you write the rest. You already have some from Lab 9.

template<class T>
inline void Bst<T>::inorder( f1Typ f1,nodeType<T> * root) const
{
    if (root->left != nullptr)
    {
        inorder(f1,root->left);
    }

    f1(root->data);

    if (root->right != nullptr)
    {
        inorder(f1,root->right);
    }
}

template<class T>
inline void Bst<T>::inorder(f1Typ f1) const
{   
    inorder(f1,this->root);
}

这是主要方法 // 使用 function 指针

int test1()
{
    BinarySearchTree<int>  intTree; 

    for (int i =0; i< 20; i++)
    {
        intTree.insertElement(i);
    }

    intTree.inOrderTraversal(f1t);  // similar to the approach used in the text - just prints, so not very useful

    return 0;

}

void f1t(int &data)
{
    cout << data << "  ";
}

 **These are the errors** 
*BinarySearchTree.h:22:1: error: template declaration of 'typedef'
   22 | typedef void (*f1Typ)(T &);  // you are not restricted to a single parameter. You
      | ^~~~~~~
BinarySearchTree.h:71:29: error: 'f1Typ' was not declared in this scope*

Answer 1

这是 BinarySearchTree.h 文件

I am creating a binary search tree template class, and want to use function pointers for the inorder traversal function, i am okay with function pointers but for some reason am lost on how to use the inorder once the code is in place. 网上没有太多其他东西对我有帮助，所以任何反馈都会很棒。

template <class T>
struct nodeType  
{
    // your write the code
        T data;
        nodeType * left;
        nodeType * right;
        nodeType(T key) :data(key), left(nullptr), right(nullptr) {}

};

template<class T>
typedef void (*f1Typ)(T &);  // you are not restricted to a single parameter. You 
                                // decide on how many parameters and provide rationale

template <class T>
class Bst // answer why class encapsulation is used - rationale
{

public:

            // you write whatever else is needed. You already have some from Lab 9.
            // insert is needed.

    void inOrderTraversal(f1Typ f1 ) const;
    
    void preOrderTraversal() const; // parameter f1 in here too. left as an exercise
    void postOrderTraversal() const; // parameter f1 in here too. left as an exercise

private:
    
    
    nodeType<T> *root;

            // you write the rest

    void inOrder(f1Typ f1, nodeType<T> *p) const;
    // you write whatever else is needed.


};

// you write the rest. You already have some from Lab 9.

template<class T>
inline void Bst<T>::inorder( f1Typ f1,nodeType<T> * root) const
{
    if (root->left != nullptr)
    {
        inorder(f1,root->left);
    }

    f1(root->data);

    if (root->right != nullptr)
    {
        inorder(f1,root->right);
    }
}

template<class T>
inline void Bst<T>::inorder(f1Typ f1) const
{   
    inorder(f1,this->root);
}

这是主要方法 // 使用 function 指针

int test1()
{
    BinarySearchTree<int>  intTree; 

    for (int i =0; i< 20; i++)
    {
        intTree.insertElement(i);
    }

    intTree.inOrderTraversal(f1t);  // similar to the approach used in the text - just prints, so not very useful

    return 0;

}

void f1t(int &data)
{
    cout << data << "  ";
}

 **These are the errors** 
*BinarySearchTree.h:22:1: error: template declaration of 'typedef'
   22 | typedef void (*f1Typ)(T &);  // you are not restricted to a single parameter. You
      | ^~~~~~~
BinarySearchTree.h:71:29: error: 'f1Typ' was not declared in this scope*