我的列表副本之一的大小在我的堆栈中打印不正确 [英] The size of one of my list copies is printing out incorrectly in my stack

问题描述

要开始，这个列表的最大大小是30，并且创建的每个列表中的项目数量存储在num_items中，通过push和pop方法我在其他地方增加和减少，但我想知道我是否需要保持这里的num_items的轨道。我会显示输出我期待与输出我得到：

To start, the max size of this list is 30 and the number of items in each list created is stored in num_items, which is incremented and decremented by push and pop methods i have elsewhere but i am wondering if i need to keep track of the num_items here as well. I will show the output i'm expecting along with the output i am getting:

现在我将显示复制我的堆栈的代码：

I will now show the code that copies my stack:

void operator=(const Stack& s)
    {
        if (s.top == NULL)
            top = NULL;
        else
        {
            top = new Node;
            top->data = s.top->data;
            Node* newP = top;

                for(Node* curr = s.top->link; curr != NULL; curr = curr->link)
                {
                    if(num_items != MAX_SIZE)
                    {
                    newP->link = new Node;
                    newP = newP->link;
                    newP->data = curr->data;
                    }
                }
        }
    }

提供输出的代码是：

Stack<int> s2(s1); // s2 declared as a copy of s1
    cout << "*declare s2 as a copy of s1 (stack s2(s1))\ns2=" << s2 << endl;
    cout << "s2.Size()=" << s2.Size() << endl;
    cout << "s2.IsEmpty()=" << ((s2.IsEmpty()) ? "T" : "F") << endl;
    cout << "s2.IsFull()=" << ((s2.IsFull()) ? "T" : "F") << endl;
    cout << "s2.Peek()=" << s2.Peek() << endl;
    cout << endl;

编辑：

初始化 num_items = 0; 在代码中我将显示如下

After initializing num_items = 0; in the code i will show below

        void operator=(const Stack& s)
    {
        if (s.top == NULL)
            top = NULL;
        else
        {
            top = new Node;
            top->data = s.top->data;
            Node* newP = top;

                for(Node* curr = s.top->link; curr != NULL; curr = curr->link)
                {
                    num_items = 0;
                    if(num_items != MAX_SIZE)
                    {
                    newP->link = new Node;
                    newP = newP->link;
                    newP->data = curr->data;
                    num_items++;
                    }
                }
        }
    }

输出我得到我的大小结果是1，我会显示整个输出再次在一个图像：

The output i get for my size turns out to be 1, i will show the whole output again in an image:

第二个编辑：

我现在已经修改我的代码如下：

I have now modified my code to the following:

void operator=(const Stack& s)
    {
        if (s.top == NULL)
            top = NULL;
        else
        {
            top = new Node;
            top->data = s.top->data;
            Node* newP = top;
                num_items = 0;
                for(Node* curr = s.top->link; curr = NULL; curr = curr->link)

                {

                    if(num_items != MAX_SIZE)
                    cout<< num_items;
                    {
                    newP->link = new Node;
                    newP = newP->link;
                    newP->data = curr->data;
                    ++num_items;
                    }
                }
        }
    }

这个虽然我的大小只计数到9而不是10，我想，因为我的循环跳过0或NULL，而是，但必须有一种方法，使它停止这样做。

with this though i my size only counts up to 9 instead of 10, i figure because my loop is skipping over 0 or "NULL" rather, but there must be a way to make it stop doing that.

推荐答案

最好复制单个列表，同时保持Node ** store指向需要设置到下一个Node *的变量：

A single list is best copied while maintaining a Node** store pointing to the variable that needs to be set to the next Node*:

void operator=( const Stack& rhs ){ // or return Stack&
  // call this->clear() to avoid memory leak
  if( rhs.top == NULL ){ top = NULL; return /* *this */; }
  Node** store = ⊤
  for( Node* curr = rhs.top; curr != NULL; curr = curr->link ){
    Node* newNode = new Node;
    num_items++;
    newNode->data = curr->data;
    *store = newNode;
    store = &newNode->link;
  }
  return /* *this */;
}

此赋值运算符将产生内存泄漏，除非注意删除任何现有条目。

This assignment operator will produce a memory leak unless care is taken to remove any existing entries. Perhaps there's already a clear() method?

后来
这些构造函数可能被使用：

Later: These constructors might be used:

Stack() : num_items(0), top(NULL) {}
Stack( const Stack& other ) {
  *this = other;
}

这种清晰的方法应该在指定的地方使用：

This clear method should be used where indicated:

void clear(){
  Node* curr = top;
  while( curr != NULL ){
    Node* next = curr->link;
    delete curr;
    curr = next;
  }
}

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