我的一份列表副本的尺寸在我的纸叠中打印不正确

Question

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:

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;
                    }
                }
        }
    }

The code that is supplying the output is:

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;

Edit:

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++;
                    }
                }
        }
    }

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

Second Edit:

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;
                    }
                }
        }
    }

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.

Answer 1

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 */;
}

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

Later: These constructors might be used:

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

This clear method should be used where indicated:

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

Answer 2

Stack<int> s2(s1);

This calls the default copy constructor and not the operator=. However, since your copy logic is implemented in the operator=, the nodes are never copied into s2.

You need to write a copy constructor and move the logic from operator= into it:

Stack(const Stack & other)
{
    // Copy other stack here
}