c - 链表垃圾值c

Question

我正在尝试做一些编程难题来学习 C，但在删除头节点时无法使链表删除正常工作。我觉得这个问题 super 简单但是我找不到!!我遇到的问题是 delete() 函数，当我尝试删除链接列表的头部时，它不会删除它，而是将其更改为垃圾值。

有人可以帮我吗？非常感谢!

这是示例输出:

Generating list...
    Inserted:   0
    Inserted:   1
    Inserted:   2
    Inserted:   3
    Inserted:   4
List:
 0  1  2  3  4 
    Deleted:    4
List:
 0  1  2  3 
    Deleted:    0
List:
 8344720  1  2  3 

这是我的源代码:

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


typedef struct Node {
    int value;
    struct Node* next;
} node;

// Append a node to the end of the linked list
int insert(node* head, int value) {
    node* current = head;

    /* Check for sentinel value. If first element inserted, overwrite      head instead of appending. */
    if (head->value == 420) {
        head->value = value;
        head->next  = NULL;
        printf("\tInserted:\t%d\n", head->value);
        return 0;
    }

    /* Traverse to end to append node */
    while (current->next != NULL)
        current = current->next;

    /* Build new node and append to tail*/
    current->next = malloc(sizeof(node));
    current->next->value = value;
    current->next->next    = NULL;

    printf("\tInserted:\t%d\n", current->next->value);
    return 0;
}

/* Accept a number and delete all nodes containing that value */
int del(node* head, int value){
    node* curr = head;
    node* prev = NULL;
    node* del  = NULL;

    printf("\tDeleted:\t%d\n", value);

    if (head == NULL) {
        printf("Can't delete value from empty list!\n");
        return 1;
    }

    /* Search list remove all instances of value. Watch for edge cases. */ 
    while (curr != NULL) {
        if (curr->value == value){
            /* Head case (lol) */
            if (curr == head) {
                del        = head;
                head       = head->next;
                curr       = head;
                free(del);
            }
            /* Tail case */
            else if (curr->next == NULL) {
                del        = curr;
                curr       = prev;
                curr->next = NULL;
                free(del);
                return 0;     /* End of list, break out of loop to avoid segfaulting */
            }
            /* Body case (base case) */
            else {
                del        = curr;
                curr       = curr->next;
                prev->next = curr;
                free(del);
            }
        }
        prev = curr;
        curr = curr->next;
    }

    return 0;
}

/* Accept head pointer and print until end of list */
int traverse(node* head) {
    node* current = head;

    if (head == NULL){
        printf("Can't traverse null list!\n");
        return 1;
    }

    printf("List:\n");
    while(current != NULL) {
        printf(" %d ", current->value);
        current = current->next;
    }
    printf("\n");

    return 0;
}

/* Let's begin our crazy experiment.... */
int main() {
    node* head  = NULL;
    head        = malloc(sizeof(node));
    head->value = 420;
    head->next  = NULL;


    printf("Generating list...\n");

    int value;
    for (value = 0; value < 5; value++)
        insert(head, value);

    traverse(head);

    del(head, 4);
        traverse(head);

    del(head, 0);
        traverse(head);

    return 0;
}

Answer 1

您正在修改 del() 函数内的头并使用 main() 中的旧头。您需要将 head 的地址传递给 del 并对其进行修改，以便更改反射(reflect)在 main 中。你可能需要这样的东西。

int del(节点 **head, int value){ 节点*当前=*头； ....

从主部分

del(&head);