C++ 中的模板类和 int main()答案

【问题标题】：Template class and int main() in C++C++ 中的模板类和 int main()
【发布时间】：2014-06-24 03:51:58
【问题描述】：

我正在尝试将“普通”类重写为模板类。我遇到了一个问题——函数int main()。我不确定问题是否确实在这里，但编译器报告“在'b'之前缺少模板参数”。我在互联网上找不到与类似问题相关的示例代码。你能帮帮我吗？

这是我找到的代码：

#include <process.h>
#include <conio.h>
#include <iostream>
#include <cstdlib>

using namespace std;

class BinarySearchTree
{
    private:
        struct tree_node
        {
           tree_node* left;
           tree_node* right;
           int data;
        };
        tree_node* root;
    public:
        BinarySearchTree()
        {
           root = NULL;
        }

        bool isEmpty() const { return root==NULL; }
        void insert(int);
        bool search(int);

};

//----------------------------------------------------

bool BinarySearchTree::search(int d)
{
    tree_node* temp = root;
    while (temp != NULL)
        {
         if (temp->data == d)
          {
            cout<<"Tree contains this node"<<endl;
            return true;
          }
        else
          {
            if (d > temp->data)
              {
                temp = temp->right;
              }
            else
              {
                temp = temp->left;
              }
          }
        }
    cout<<"Tree does not contain this node"<<endl;
    return false;
}

void BinarySearchTree::insert(int d)
{
    tree_node* t = new tree_node;
    tree_node* parent;
    t->data = d;
    t->left = NULL;
    t->right = NULL;
    parent = NULL;

  if(isEmpty()) root = t;
  else
  {
    tree_node* curr;
    curr = root;
    // Find the Node's parent
    while(curr)
    {
        parent = curr;
        if(t->data > curr->data) curr = curr->right;
        else curr = curr->left;
    }

    if(t->data < parent->data)
       parent->left = t;
    else
       parent->right = t;
  }
}

//----------------------------------------------------

int main()
{
    BinarySearchTree b;
    int ch,tmp,tmp1,tmp2;
    while(1)
    {
       cout<<endl<<endl;
       cout<<" Binary Search Tree Operations "<<endl;
       cout<<" ----------------------------- "<<endl;
       cout<<" 1. Insertion/Creation "<<endl;
       cout<<" 2. Does Binary Searching Tree contains this node? "<<endl;
       cout<<" 3. Exit "<<endl;
       cout<<" Enter your choice : ";
       cin>>ch;
       switch(ch)
       {
           case 1 : cout<<" Enter Number to be inserted : ";
                    cin>>tmp;
                    b.insert(tmp);
                    break;
           case 2 : cout<<" Enter data to be found : ";
                    cin>>tmp;
                    b.search(tmp);
                    break;
           case 3 : system("pause");
                    return 0;
                    break;
       }
    }
}

我试图重写它：

#include <process.h> 
#include <conio.h>
#include <iostream>
#include <cstdlib>

using namespace std;

template <class T>
class BinarySearchTree
{
    private:
        struct tree_node
        {
           tree_node* left;
           tree_node* right;
           T data;
        };
        tree_node* root;
    public:
        BinarySearchTree<T>()
        {
           root = NULL;
        }

        T isEmpty() const { return root==NULL; }
        T insert(T);
        T search(T);

};

//----------------------------------------------------

template <class T>T BinarySearchTree<T>::search(T d)
{
    tree_node* temp = root;
    while (temp != NULL)
        {
         if (temp->data == d)
          {
            cout<<"Tree contains this node"<<endl;
            return true;
          }
        else
          {
            if (d > temp->data)
              {
                temp = temp->right;
              }
            else
              {
                temp = temp->left;
              }
          }
        }
    cout<<"Tree does not contain this node"<<endl;
    return false;
}


template <class T>T BinarySearchTree<T>::insert(T d)
{
    tree_node* t = new tree_node;
    tree_node* parent;
    t->data = d;
    t->left = NULL;
    t->right = NULL;
    parent = NULL;

  if(isEmpty()) root = t;
  else
  {
    tree_node* curr;
    curr = root;

    while(curr)
    {
        parent = curr;
        if(t->data > curr->data) curr = curr->right;
        else curr = curr->left;
    }

    if(t->data < parent->data)
       parent->left = t;
    else
       parent->right = t;
  }
}

//----------------------------------------------------

int main()
{
    BinarySearchTree b;
    int ch,tmp,tmp1,tmp2;
    while(1)
    {
       cout<<endl<<endl;
       cout<<" Binary Search Tree Operations "<<endl;
       cout<<" ----------------------------- "<<endl;
       cout<<" 1. Insertion/Creation "<<endl;
       cout<<" 2. Does Binary Searching Tree contains this node?"<<endl;
       cout<<" 3. Exit "<<endl;
       cout<<" Enter your choice : ";
       cin>>ch;
       switch(ch)
       {
           case 1 : cout<<" Enter Number to be inserted : ";
                    cin>>tmp;
                    b.insert(tmp);
                    break;
           case 2 : cout<<" Enter data to be found : ";
                    cin>>tmp;
                    b.search(tmp);
                    break;
           case 3 : system("pause");
                    return 0;
                    break;
       }
    }
}

【问题讨论】：

BinarySearchTree 一个模板，而不是一个类型。它需要模板参数......就像你不做std::vector v;一样。
你的重写没有任何意义。为什么isEmpty()、insert() 和search() 返回T？而这个BinarySearchTree<T>() { ... } 应该是BinarySearchTree() { ... }
@Praetorian 我正在关注指南codingunit.com/cplusplus-tutorial-templates
@Anakin, Stack<int> int_stack;
“这是我找到的代码” - 这是哪个？你找到的代码还是重写后的代码？无论如何，您可能会更好地学习语言。正如许多人所证明的那样，没有捷径可走。

标签： c++ algorithm binary-search-tree class-template

【解决方案1】：

错误是显式的，你需要给它一个模板参数，例如：

BinarySearchTree<int> b;

【讨论】：

【解决方案2】：

除了模板实例化问题，我还可以看到其他问题。

如果您使用插入方法添加一个已经在树中的值会发生什么。它将在右侧添加一个新节点。从 BST 概念来看，这是错误的。
Insert 方法实际上根本不返回任何内容。

【讨论】：