迭代时列表结构发生变化

Question

我正在使用以下代码迭代链表

void display()
{
    if (head == NULL)
    {
        printf("\n");
        return;
    }
    struct node *current = head;
    while (current->next != NULL)
    {

        printf("%3c", current->data); // *(current).data

        current = current->next; // current = *(current).next;

    } //printf( "\n" );
    printf("%3c", current->data);
    printf("    <-->  ");
    while (current != NULL)
    {
        printf("%3c", current->data); // *(current).data
        current = current->prev;      // current = *(current).prev;
    }
    printf("\n");
}

我在这个函数中遇到了分段错误，我无法计算
为什么会发生这种情况。
我运行调试器并截取了屏幕截图：

以上两张图是在迭代时调用显示
在 while 循环中。奇怪的是在第一张图片
元素是 Y->O->R->x->K
而当迭代在 while 循环中继续时
遇到R下一个数据是st运行gely some[=13=]0
我从来没有插入那个，它是如何改变的
相同的迭代，因为没有修改发生

最小可重现代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFER_SIZE 50
#define MAX_LEN 30
char get(int index);
int search(char);
struct twoInts
{
    int int1;
    int int2;
};

struct node
{ // list 'node' struct
    char data;
    struct node *next;
    struct node *prev;
};

void init();
void display();

struct node *head;

int main()
{
    int index;
    char key;

    struct twoInts *arr[MAX_LEN];
    char buffer[BUFFER_SIZE];
    init();

    int i = 0;
    int summation[10] = {89, 79, 82, 75, 85, 76, 65, 66, 83};
    for (; i < 8; i++)
    {
        int sum = summation[i];
        insert((char)sum);
        display();
    }

    char removeList[] = {'B', 'S', 'A', 'O', 'R', 'K', 'Y', 'U', 'L', '[=11=]'};
    i = 0;

    // insert again
    char addList[] = "ZPSLVMBCT";
    i = 0;
    while ((key = addList[i]) != '[=11=]')
    {
        insert(key);
        display();
        i++;
    }
    key = 'x';
    index = 2;
    insertAfter(key, index);
    printf(xyz-1\n");
    int length = len();
    printf("xyz-2\n");

    // printf("\ninsert %c after index %d: (%d)\n", key, index, length);
    display();
}

/* Initialize the list. */
void init()
{
    head = NULL;
}
int len()
{
    struct node *tmp = head;
    int length = 0;
    while (tmp != NULL)
    {
        length++;
        tmp = tmp->next;
    }
    return length;
}
/* Print the content of the list. */
void display()
{
    if (head == NULL)
    {
        printf("\n");
        return;
    }
    struct node *current = head;
    while (current->next != NULL)
    {

        current = current->next; // current = *(current).next;

    } //printf( "\n" );
    while (current != NULL)
    {
        current = current->prev; // current = *(current).prev;
    }
}

void insert(char c) //  at the end
{
    /* special case: list is empty, need to change head  */
    if (head == NULL)
    { /* the list is empty */
        head = malloc(sizeof(struct node));
        head->data = c;
        head->next = NULL;
        head->prev = NULL;
    }
    else
    {
        struct node *tmp = head;
        while (tmp->next != NULL)
            tmp = tmp->next;
        struct node *last = malloc(sizeof(struct node));
        last->data = c;
        last->next = NULL;
        last->prev = tmp;
        tmp->next = last;
    }
}

void insertAfter(char c, int index)
{

    struct node *tmp = head;
    int currIndex = 0;
    while (tmp->next != NULL)
    {
        if (currIndex == index)
            break;

        currIndex++;
        tmp = tmp->next;
    }
    if (currIndex == index)
    {
        struct node *newNode = malloc(sizeof(struct node));
        newNode->data = c;
        newNode->prev = tmp;
        newNode->next = tmp->next;
        struct node *nextNode = tmp->next;
        if (tmp->next != NULL)
        {
            tmp->next = &newNode;
            nextNode->prev = &newNode;
        }
    }
}

Answer 1

好的，我已经解决了你的问题。问题出在您声明 struct node newNode 的 insertAfter 函数中。这会在堆栈上创建一个对象，而列表的其余部分存储在堆上。当 insertAfter 函数退出时，这会导致堆栈展开并且内存无法访问。您应该将此行替换为对 malloc.

的调用

迭代时列表结构发生变化

List structure changing while iterating

c

segmentation-fault