Question

我一直在为我的CS类中的作业编写C程序，该程序成功编译但在运行时出现分段错误错误。该作业处理linkedLists;我们必须在名为linkedlist.h的头文件中描述和声明的方法，并实现一个名为linkedlist.c的文件。提供了一个名为listtest.c的文件，用于测试该方法。

我的代码（linkedlist.c，评论来自我们给出的头文件，描述了方法应该如何工作）：

#include "linkedlist.h"
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>


/* Alloc a new node with given data. */
struct ListNode* createNode(int inputData)
{

    struct ListNode *newNodeCN;
    newNodeCN->data = inputData;
    return newNodeCN;
}

/* Insert data at appropriate place in a sorted list, return new list head. */
struct ListNode* insertSorted(struct ListNode* head, int inputData)
{
    printf("insertsorted started \n");

    struct ListNode * nextIS = NULL;
    struct ListNode * newNodeIS = NULL;
    struct ListNode * currIS = head;
    struct ListNode * listHeadIS = currIS;
    if (currIS == NULL)
    {
        listHeadIS = createNode(inputData);
        return listHeadIS;
    }
    while (currIS->next != NULL)
    {
        nextIS = currIS->next;

        if (currIS->data < inputData)
        {
            if (nextIS->data >= inputData)
            {

                nextIS->next = createNode(inputData);
                newNodeIS = nextIS->next;
                if (newNodeIS->data > listHeadIS->data)
                {
                    listHeadIS = newNodeIS;
                }
            }
        }
        currIS = currIS->next;
    }

    return listHeadIS;
}

/* Remove data from list pointed to by headRef, changing head if necessary.
* Make no assumptions as to whether the list is sorted.
* Memory for removed node should be freed.
* Return 1 if data was present, 0 if not found. */
int removeItem(struct ListNode** headRef, int data)
{
    struct ListNode * tempRem = *headRef;
    int filterVal = data;

    while (tempRem->next != NULL)
    {
        if (tempRem->data == filterVal)
        {
            free(tempRem);
            tempRem = tempRem->next;
            return 1;
        }
    }


    return 0;
}
/* Insert data at head of list, return new list head. */
struct ListNode* push(struct ListNode* head, int data)
{
    printf("push started \n");
    int dataPush = data;

    struct ListNode * tempPush = (struct  ListNode*)malloc(sizeof(struct ListNode));
    tempPush->data = dataPush;
    tempPush->next = head;
    *head = *tempPush;
    return tempPush;
}

/* Remove and return data from head of non-empty list, changing head.
* Memory for removed node should be freed. */
int pop(struct ListNode** headRef)
{
    struct ListNode * tempPop = *headRef;
    int tempData;

    tempData = tempPop->data;
    free(tempPop);
    tempPop = tempPop->next;

    return tempData;
}
/* Return length of the list. */
int listLength(struct ListNode* head)
{
    int i;
    while (head->next != NULL)
    {
        i++;
        head = head->next;
    }
    return i;
}
/* Print list data on single line, separated with spaces. */
void printList(struct ListNode* head)
{
    printf("PrintList Started \n");
    if (head != NULL)
    {

        while (head->next != NULL)
        {

            printf("%d\n", head->data);
            head = head->next;
        }
    }
}
/* Free memory used by the list. */
void freeList(struct ListNode* head)
{
    while (head != NULL)
    {
        free(head);
        head = head->next;
    }
}
/* Reverse order of elements in the list */
void reverseList(struct ListNode** headRef)
{
    struct ListNode * origRL = *headRef;
    struct ListNode * nextRL = NULL;
    struct ListNode * prevRL = NULL;
    while (origRL->next != NULL);
    {
        nextRL = origRL->next;
        prevRL = origRL;
        origRL = nextRL;
        origRL->next = prevRL;
   }

}

listtest.c中的代码（我没有写这个）：

#include <stdio.h>
#include <stdlib.h>
#include "linkedlist.h"

int main(int argc, char** argv)
{
  int i, n;
  struct ListNode* head = NULL;
  struct ListNode* stack = NULL;

  printf("empty list: ");
  printList(head);

  for(i = 0; i < 23; ++i)
  {
    n = (i*17+11) % 23;
    head = insertSorted(head, n);
    printf("sort succesful /n");
    stack = push(stack, n);
  }

  printf("filled list: ");
  printList(head);
  printf("list length = %d\n", listLength(head));

  printf("filled stack: ");
  printList(stack);
  printf("stack size = %d\n", listLength(stack));

  for(i = -4; i < 25; i+=4)
  {
    n = removeItem(&head, i);
    if(!n) printf("remove did not find %d\n", i);  
  }

  printf("list after removes: ");
  printList(head);
  printf("list length = %d\n", listLength(head));

  for(i = 0; i < 5; ++i)
  {
    printf("pop: %d\n", pop(&stack));
  }

  printf("stack after pops: ");
  printList(stack);
  printf("stack size = %d\n", listLength(stack));

  reverseList(&head);
  printf("list after reverse: ");
  printList(head);

  freeList(head);
  head = NULL;

  freeList(stack);
  stack = NULL;

  return 0;
}

根据Valgrind和GDB的说法，分段错误是由主要的东西引起的。 Valgrind给了我错误：

 Access not within mapped region at address 0x6FFFFFFE3
==6300==    at 0x400953: main

我的问题是究竟是什么导致了分段错误，我该如何修复它，并且我的代码中的任何其他内容都会导致分段错误？我不允许编辑listtest.c，因此任何更改都必须在linkedlist.c中。谢谢。

Answer 1

struct ListNode * newNodeCN; newNodeCN-＆gt; data = inputData;实际上没有分配新节点
int listLength（struct ListNode * head） - 我从未初始化。
oid freeList（struct ListNode * head） - 免费，然后取消引用

Answer 2

在函数insertSorted中，条件if（newNodeIS-＆gt; data ...）对指针进行解映射而不验证它是否为NULL，那就是分段错误的来源。尝试修复报告：）

Answer 3

首先在函数createNode中，使用元素＆＃34; data＆＃34;但对于newNodeCN来说，没有malloc真正的内存，它的类型是struct ListNode。此外，＆＃34;分段错误＆＃34;通常在你参考引用错误的内存地址时出现（例如指针u不是malloc，或者是数组之外的地址等等。）

运行C程序时出现分段错误

3 个答案: