[C语言]利用二级指针进行链表的添加和删除处理

天道酬勤，每日记点笔记也是蛮有意思的。

今天温习了下 POINTERS ON C 书中的链表一章，记录下使用二级指针对链表进行添加和删除处理。

插入函数：

#define TRUE 1
#define FALSE 0
/*
  * brief： Single Linked List
  * para:   head       -> the head of list
  *           newValue -> item which to be inserted
*/
int sll_insert(node **head,int newValue)
{
  node * curr;
  node *new;

  // find the position
  while((curr = *head)  != NULL && curry->value <newValue)
           head = &curr->next;
 
  // new
  new = (node *)malloc(sizeof(node));
  if(new == NULL)return FALSE;
 
  //insert
  new->value = newValue;
  new->next = curr;

  *head = new;
  return TRUE;
}

删除函数：

typedefbool(* remove_fn)(node const* v);   


// 写法一：
void remove_if(node ** head, remove_fn rm)
{
  node *curr;
  
   while( (curr = *head) != NULL)
  {
      // notice entry and curr point both point to the same one
      node *entry = curr;//delete it !!
      if(rm(entry)){
         *head = curr->next;   
         free(entry);
      }else{
        head = &curr->next;
      }
  }
}

不过注意到 写法一 中重复比较多，例如curr 其实都没必要存在！所以我更推荐写法二。

// 写法二：
void remove_if(node ** head, remove_fn rm)
{
    for(node** curr = head; *curr; )
    {
        node * entry = *curr;
        if(rm(entry))
        {
            *curr = entry->next;
            free(entry);
        }
        else
            curr = &entry->next;
    }
}