C ++編程錯誤-運行時錯誤

Question

執行下面的C ++代碼時出現運行時錯誤。 有人可以幫我解決為什么出現此運行時錯誤。

#include<iostream>
using namespace std;

struct node
{
   int data;
   struct node *left;
   struct node *right;
   struct node *rlink;
};

struct qnode
{
   struct node *lnode;
   int level;
};

struct node* newnode (int n)
{
   struct node *temp;
   temp= new struct node;
   temp->data=n;
   temp->left=NULL;
   temp->right=NULL;
   temp->rlink=NULL;
   return temp;
}

void link (struct node *n, int level)
{
  struct qnode *qn;
  struct qnode *current, *next;
  struct qnode nextd;
  next = &nextd;

  (next->lnode)->data=5;
  cout << (next->lnode)->data << endl;

}


int main()
{
    struct node *root = newnode(10);
    root->left        = newnode(8);
    root->right       = newnode(2);
    root->left->left  = newnode(3);


    link (root, 0);
    return 0;


  }

Answer 1

在鏈接功能中，您這樣做：

next = &nextd;

nextd未初始化，並且當其地址分配給next時包含垃圾值。 接下來的幾行嘗試訪問它，這將導致訪問沖突錯誤。

Answer 2

問題出在鏈接中：

void link (struct node *n, int level)
{
  struct qnode *qn;
  struct qnode *current, *next;
  struct qnode nextd;
  // BUG 1 = nextd is uninitialized
  // BUG 2 - nextd is a stack-based variable, becomes junk when function exits
  next = &nextd; 
  // Becuase nextd is uninitialized, next->lnode points to garbage. Kaboom!
  (next->lnode)->data=5;
  cout << (next->lnode)->data << endl;

}