C示例从双向链接列表中删除数据

#include <stdio.h>

#include <stdlib.h>



struct node {

   int data;

   struct node *prev;

   struct node *next;

};



struct node *head = NULL;

struct node *last = NULL;

struct node *current = NULL;



//display the list

void printList() {

   struct node *ptr = head;



   printf("\n[head] <=>");

   //start from the beginning

   while(ptr != NULL) {        

      printf(" %d <=>",ptr->data);

      ptr = ptr->next;

   }



   printf(" [last]\n");

}



void print_backward() {

   struct node *ptr = last;



   printf("\n[last] <=>");

   //start from the beginning

   while(ptr != NULL) {        

      printf(" %d <=>",ptr->data);

      ptr = ptr->prev;

   }



   printf(" [head]\n");

}



//Create Linked List

void insert(int data) {

   // Allocate memory for new node;

   struct node *link = (struct node*) malloc(sizeof(struct node));



   link->data = data;

   link->prev = NULL;

   link->next = NULL;



   // If head is empty, create new list

   if(head==NULL) {

      head = link;

      return;

   }



   current = head;



   // move to the end of the list

   while(current->next!=NULL)

      current = current->next;



   // Insert link at the end of the list

   current->next = link;

   last = link;

   link->prev = current;

}



void remove_data(int data) {

   int pos = 0;

   struct node *pre_node;



   if(head==NULL) {

      printf("Linked List not initialized");

      return;

   }



   if(head->data == data) {

      if(head->next != NULL) {

         head->next->prev = NULL;

         head = head->next;

         return;

      } else {

         head = NULL;

         printf("List is empty now");

         return;

      }

   } else if(head->data != data && head->next == NULL) {

      printf("%d not found in the list\n", data);

      return;

   }



   current = head;



   while(current->next != NULL && current->data != data) {

      pre_node = current;

      current = current->next;

   }        



   if(current->data == data) {

      pre_node->next = pre_node->next->next;



      if(pre_node->next != NULL) {          // link back

         pre_node->next->prev = pre_node;

      } else

         last = pre_node;



      free(current);

   } else

      printf("%d not found in the list.", data);



}



int main() {

   insert(10);

   insert(20);

   insert(30);

   insert(1);

   insert(40);

   insert(56);



   printList();

   remove_data(20);



   printList();

   print_backward();



   return 0;

}