C++堆栈实现弹出功能不起作用

Question

我正在实现一个带有链接列表的堆栈以供审查。我的弹出功能无法正常工作。我用 main 中的节点创建了一个测试，它做的事情与我的 linkedList 函数所做的完全相同，但我每次都遇到段错误。这是代码。

#include <iostream>

struct Node{
  int data;
  Node* next;
};

class Stack{
  private:
    Node head;
    int size;
  public:
    Stack();
    ~Stack();
    int getSize();
    void push(int val);
    int pop();
    void printStack();
};

Stack::Stack(){
  head.data = 0;
  head.next = NULL;
}

Stack::~Stack(){
}

int Stack::getSize(){
  return size;
}

void Stack::push(int val){
  Node newNode;
  newNode.data = val;
  if(size == 0) newNode.next = NULL;
  else newNode.next = head.next;
  head.next = &newNode;
  size++;
}

int Stack::pop(){
  int returnVal = head.next->data;
  head.next = head.next->next;
  return returnVal;
}
}


int main(){
  Stack s;
  s.push(8);
  s.push(30);
  s.push(40);
  int value = s.pop();
  int value2 = s.pop(); //segmentation fault
  std::cout<<value<<"\n"<<value2<<"\n"; 


/* This works correctly
  Node head;
  head.data = 0;
  head.next = NULL;
  Node n1;
  n1.data = 5;
  n1.next = NULL;
  head.next = &n1;
  Node n2;
  n2.data = 8;
  n2.next = head.next;
  head.next = &n2;
  Node n3;
  n3.data = 30;
  n3.next = head.next;
  head.next = &n3;

  int value = head.next->data;
  std::cout << value << "\n";
  head.next = head.next->next;
  value = head.next->data;
  std::cout << value << "\n";
*/
  return 1;
}

Answer 1

问题在于您如何创建节点。在你的例子中，你创建了一个局部变量，它只存在于函数 push() 的范围内。你可以使用这样的东西。

void Stack::push(int val){
  Node* newNode = new Node;
  newNode->data = val;
  /* ... */ 
}

编辑:添加了堆栈的一个版本(绝不是完整的)

#include <iostream>

struct Node{
  int data;
  Node* next;
};

class Stack {
  private:
    Node* head;
    int size;

  public:
    Stack();
    ~Stack();
    int getSize();
    void push(int val);
    int pop();
    void printStack();
};

Stack::Stack() : head(0), size(0)
{
}

Stack::~Stack(){
}

int Stack::getSize(){
  return size;
}

void Stack::push(int val){
  Node* newNode = new Node;
  newNode->data = val;
  newNode->next = head;

  head = newNode;
  size++;
}

int Stack::pop(){
    if(head != 0)
    {
        int val = head->data;

        Node* tmp = head;
        head = head->next;

        tmp->next = NULL;
        delete tmp;

        size--;

        return val;
    }
    else
    {
        return -1; // what happens if stack is empty ?      
    }
}