c - 插入链表

Question

我正在尝试在链接列表中插入节点。我尝试在特定节点的前面、末尾和后面插入节点。我认为代码很好并且应该可以工作。然而，这段代码给出了运行时错误。请解释为什么会出现运行时错误？

Insertion in a linked list

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

// A linked list node
struct node
{
    int data;
    struct node *next;
};


void push(struct node* head, int new_data)
{
/* 1. allocate node */
struct node* new_node = (struct node*) malloc(sizeof(struct node));

/* 2. put in the data  */
new_node->data  = new_data;

/* 3. Make next of new node as head */
new_node->next = head;

/* 4. move the head to point to the new node */
head   = new_node;
}

 /* Given a node prev_node, insert a new node after the given prev_node */
void insertAfter(struct node* prev_node, int new_data)
{
/*1. check if the given prev_node is NULL */
if (prev_node == NULL)
{
  printf("the given previous node cannot be NULL");
  return;
}

/* 2. allocate new node */
struct node* new_node =(struct node*) malloc(sizeof(struct node));

/* 3. put in the data  */
new_node->data  = new_data;

/* 4. Make next of new node as next of prev_node */
new_node->next = prev_node->next;

/* 5. move the next of prev_node as new_node */
prev_node->next = new_node;
}


void append(struct node* head, int new_data)
{
/* 1. allocate node */
struct node* new_node = (struct node*) malloc(sizeof(struct node));

struct node *last = head;  

/* 2. put in the data  */
new_node->data  = new_data;

/* 3. This new node is going to be the last node, so make next of it as NULL*/
new_node->next = NULL;

/* 4. If the Linked List is empty, then make the new node as head */
if (head == NULL)
{
   head = new_node;
   return;
}

/* 5. Else traverse till the last node */
while (last->next != NULL)
    last = last->next;

/* 6. Change the next of last node */
last->next = new_node;
return;
}

// This function prints contents of linked list starting from the given node
void printList(struct node *node)
{
  while (node != NULL)
  {
     printf(" %d ", node->data);
     node = node->next;
  }
}

/* Driver program to test above functions*/
int main()
{
   /* Start with the empty list */
   struct node* head = NULL;


  append(head, 6);
  push(head, 7);
  push(head, 1);
  append(head, 4);
  insertAfter(head->next, 8);
  printf("\n Created Linked list is: ");
  printList(head);

  getchar();
  return 0;
}

Answer 1

您丢失head指针的每个地方

您应该在所有函数中保留其地址，使用struct node**，并更新指针使用 *head 和 (*prev_node)

void push(struct node** head, int new_data)
{ //... 
  // *head
}

void insertAfter(struct node** prev_node, int new_data)
{ //... 
  // (*prev_node)
}

void append(struct node** head, int new_data)
{ //... 
  // *head
}

参见here

^{PS:可能存在逻辑错误}

此外，请确保在完成所有操作后使用 free() 调用释放内存。