C - 链表 - 删除头部 - 段错误

Question

我正在为一个类(class)解决一个问题，我们正在学习 C 语言的链表。我得到了一段代码需要完成，特别是删除节点部分，我在删除头部时遇到了问题。每次我尝试删除 head 时，我都会收到段错误。谁能告诉我我做错了什么？

编辑2 除了查找和删除功能，我的老师什么都写了。

我已经修复了来自莫斯科的绅士和 Petriuc 先生指出的明显错误，但是代码仍然无法运行。编译通过了，但是head还是有问题。

完整代码如下:

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

#include "linkedList.h"

// keep an unsorted array of char *'s, strings.

/*
  Create an empty node, return 0 if fail, 1 if succeed
 */
struct node * createNode() {
  struct node *p = (struct node *) malloc(sizeof(struct node));
  if (p == NULL) return 0;

  p->prev = p->next = NULL;
  p->data = NULL;
}


/*
  Lookup string in the list, return pointer to node of first occurence, NULL if not found.
 */
struct node * lookup(struct node *head, char *s) {
  struct node *p;
  for(p=head; p!=NULL; p=p->next){
    if(strcmp(s,p->data)==0){
      return p;
    }
  // just like print, but check if strcmp(s, p->data) == 0, and if so then return p
  }
  return NULL;
}


/*
  Insert new string into the linked list, return 1 if success, 0 if fail.
 */
int insert(struct node **head, char *newS, int insertDuplicate) {
  struct node *p = lookup(*head, newS);

  if (p == NULL || insertDuplicate) {
    // create a new node, put it at the front.
    p = createNode();
    if (p == NULL) return 0;

    // put the string in the new node
    p->data = (char *) malloc(sizeof(char) * (1 + strlen(newS)));
    if (p->data == NULL) return 0;
    strcpy(p->data, newS);

    // note: make changes and use old head before setting the new head...
    p->next = *head;   // next of new head is previous head

    if (*head != NULL)
      (*head)->prev = p; // previous of old head is new head

    *head = p;         // set the new head
  }

  return 1;
}

/*
  Remove string from list if found, return 1 if found and deleted, 0 o/w.
 */
int delete(struct node **head, char *s) {
  struct node *p,*pr,*ne;
  // first do a lookup for string s, call lookup.
  p=lookup(*head, s);

  if(p==*head){
    *head = p->next;
    free(p);
    return 1;
  }

  if(p!=NULL){
     printf("%s",p);
     pr = p->prev;
     ne = p->next;

     free(p->data);
     free(p);

    if(pr==NULL||ne==NULL){
      return 0;
    }
     pr->next=ne;
     ne->prev=pr;
  // if lookup returns NULL, done, return 0.
  // if lookup returns p, not NULL,
  // pr = p->prev, ne = p->next
  //  set pr->next to ne, ne->prev to pr
  //  but what if pr or ne is NULL
  // and note that we need node **head because if delete head,
  // need to update head pointer back in calling function, in
  // here if you want head probably do *head.  like in insert.
  // also, before the pointer to the one you're deleting is gone,
  // free p->data and p.
    return 1;
  }
  return 0;
}


void print(struct node *head) {
  struct node *p;
  for(p = head; p != NULL ; p = p->next) {
    printf("%s\n", p->data);
  }
}

Answer 1

你在做什么

p->next = *head;

但是 p 没有赋值给任何地方。