雙鏈列表從列表中刪除字符串

Question

我是C的新手，需要您的幫助。 我已經發布了我所遇到的大型鏈表問題的2部分，因為我不想用大代碼轟炸你們所有人，所以我分部分進行。 不過，這是一個新問題，因此，如果您能向我解釋，我將一如既往地感謝您。

我在雙向鏈接列表中有一個函數，該函數應該刪除列表中的字符串，但是似乎有一個問題，它沒有刪除任何內容。 事實上，這讓我陷入困境，我什么也無法輸入。 我想粘貼我的代碼，以便您更好地了解我正在處理的內容。 愛你的幫助！

這是我的結構節點：

 struct node
 {
 char data[100];
 struct node *previous;  // Points to the previous node
 struct node *next;   // Points out to the next node
 }*head, *last;

這是我的函數，稱為：delete_from_middle

 char delete_from_middle(char words[99])
 {
  struct node *temp,*var,*temp1;
  temp=head;
  strcpy(temp->data, words);

  while (temp!=NULL)
  {
    if (temp->data == words)
    {
        if (temp->previous==NULL)
        {
            free(temp);
            head=NULL;
            last=NULL;
            return 0;
        }
        else
        {
            var->next=temp1;
            temp1->previous=var;
            free(temp);
            return 0;
        }
    }
    else
    {
        var=temp;
        temp=temp->next;
        temp1=temp->next;
      }
   }
  printf(" Data deleted from list is %s \n", words);
  return 0;
 }

這是我將其分配給我的主機的地方

 int main()
 {
  char loc[99];
  char words[99];
  int i, dat;

  head=NULL;

printf("Select the choice of operation on link list");
printf("\n1.) Insert At Begning\n2.) Insert At End\n3.) Insert At Middle");
printf("\n4.) Delete From End\n5.) Reverse The Link List\n6.) Display List\n7.)Exit");

while(1)
{
    printf("\n\n Enter the choice of operation you want to do ");
    scanf("%d",&i);

    switch(i)
    {
        case 1:
        {
            printf("Enter a word you want to insert in the 1st node ");
            scanf(" %s",words);

            insert_beginning(words);
            display();
            break;
        }
        case 2:
        {
            printf("Enter a word you want to insert in the last node ");
            scanf(" %s",words);
            insert_end(words);
            display();
            break;
        }
        case 3:
        {
            printf("After which data you want to insert your new data ");
            scanf(" %s",words);

            printf("Enter the data you want to insert in list ");
            scanf(" %s",loc);

            insert_after(words, loc);
            display();
            break;
        }
        case 4:
        {
            delete_from_end();
            display();
            break;
        }
        case 5:
        {
            printf("Enter the value you want to delete");
            scanf(" %s",words);
            delete_from_middle(words);
            display();
            break;
        }

如果代碼看起來很長，我真的很抱歉，但是我真的想弄清楚該怎么做。 有什么幫助嗎？ 請讓我知道我是否遺漏了一些東西，或者我的問題沒有正確提出。

Answer 1

好吧，線

if (temp->data == words) {

當然不會執行您期望的操作：您正在比較指針，而不是指針后面的字符串！ 為此使用strcmp() 。

---

確切地說： ==運算符用於比較兩個數組，但是這些數組會衰減為指向其第一個元素的指針，代碼等效於

if (&temp->data[0] == &words[0]) {

但這可能是您以后應該學習的一課，它會使足夠有經驗的C程序員感到困惑...

Answer 2

您可以通過將temp設置為指向列表的開頭來啟動該功能。 然后用搜索字符串替換head-> data。 顯然現在head-> data ==單詞，而上一個== null，所以head被釋放，函數返回零

Answer 3

您的代碼非常復雜，似乎包含多個問題。 您可能應該將函數切成較小的部分，以更輕松地發現錯誤。

例如：

struct node *find(char words[99])
{
  struct node *temp;
  temp = head;
  while (temp != NULL)
  {
    if (strcmp(temp, words) == 0)
      return temp;
  }
  return NULL;
}

void deleteNode(struct node *n)
{
  if (n->previous != NULL)
    n->previous->next = n->next;
  else // n is head
    head = n->next;
  if (n->next != NULL)
    n->next->previous = n->previous;
  else
    last = n->previous;
  free(n);
}

char delete_from_middle(char words[99])
{
  struct node *target = find(words);
  if (target != NULL)
    deleteNote(target);
}

Answer 4

您的代碼中有問題。 嘗試：遍歷整個鏈表，例如

for(node temp=head; temp!=null; temp=temp->next)
{
   if(temp->data==words)
   {
        //update links
        temp->previous=temp->next; 
        temp->next->previous=temp->previous->next;
        break;
    }
 }
free (temp); //delete/free node

Answer 5

First in while loop, if condition is always true because of this line -
strcpy(temp->data, words);

Now there are two parts in if -> first ( if(temp->previous == NULL)
)  if there is only a single element in the list then list will set
to null by setting head = NULL and last = NULL;

Second part -> If list has more than one elements then your
operations are 

var->next=temp1;  //This one is wrong cause var is not assigned its only declared
temp1->previous = var; //this one is causing problem  free(temp); you freed the    memory that was allocated for temp but
//forget to delete temp . 
return 0;
//At last your element is not actually deleted and you freed the
//memory that was allocated for that element.



For deleting a specific element simplest code is -> 
char delete_from_middle(char words[99])  
{   
struct node *h;
h = head; 
while ( h! = NULL )   {
    if ( strcmp(h->data, words) == 0)
    {
        if ( h->previous == NULL )
        {
           if( head == last )
             {
               head = NULL;
               last = NULL;
             }
           else
             {
               head = head->next;
               head->previous = NULL;

              }
        }
        else
        { 
          if( h->next!=NULL ) h->next->previous = h->previous;
          h->previous->next = h->next;
        }
      printf(" Data deleted from list is %s \n", words);   
      free(h);
      return 0;
    }
   h = h->next;
 } 
    printf(" Data not found");     
    return 0;  }

Answer 6

代碼中有很多問題，而刪除列表的完整性並沒有得到維護。 以下是從列表中刪除節點的方法：

void delete_from_middle(char words[99])
{
  struct node *temp;
  temp=head;

  while (temp!=NULL)
  {
    if (strcmp(temp->data,words)==0) //this is the data we are looking for, go and delete this
    {
        if (temp->previous==NULL) //this is the head
        {
            head=temp->next;
            temp->next->previous=NULL;
            free(temp);
            printf(" Data deleted from list is %s \n", words);
            return;
        }
        else if(temp->next==NULL) //this is last node
        {
            temp->previous->next=NULL;
            free(temp);
            printf(" Data deleted from list is %s \n", words);
            return;
        }
        else
        {
            temp->previous->next=temp->next;
            temp->next->previous=temp->previous;
            free(temp);
            printf(" Data deleted from list is %s \n", words);
            return;
        }
    }
    else //this node does not contain the data, go to the next node
    {
        temp=temp->next;
    }
  } 
  //search ended
  printf(" Data not found\n");
  return;
}