C語言刪除雙向連結串列中資料項程式

建立一個雙向連結串列，並刪除此雙向連結串列中的資料項的範例程式，將以下程式碼儲存到一個原始檔中：remove_data_from_doubly_linked_list.c， 如下所示 -

#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(40);
    insert(50);
    insert(60);

    printList();
    remove_data(20);
    remove_data(50);
    printList();
    print_backward();

    return 0;
}

執行上面程式，得到以下結果 -

[head] <=> 10 <=> 20 <=> 30 <=> 40 <=> 50 <=> 60 <=> [last]

[head] <=> 10 <=> 30 <=> 40 <=> 60 <=> [last]

[last] <=> 60 <=> 40 <=> 30 <=> 10 <=> [head]