c - 为什么我不能在此链表的索引 0(头)处插入新节点？

Question

代码:

/*
 * File: problem5.c
 * Author: levihackwith
 * Description: Write a Pop() function that is the inverse of Push(). Pop() takes a non-empty list, deletes the head node, and returns the head node's data.
 */

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

struct node { // Our custom node data type
    int data;
    struct node *next;
};

/*
 * Adds a node to a linked list.
 *
 * This method was taken from the Appendix of the LinkedListProblems.pdf file from Stanford University.
 */
void Push(struct node** headRef, int newData) {
    struct node* newNode = malloc(sizeof (struct node)); // allocate node
    newNode->data = newData;
    newNode->next = (*headRef);
    (*headRef) = newNode;
};

void InsertNth(struct node** headRef, int insertAt, int newData) {
    struct node* newNode = malloc(sizeof (struct node)); // allocate node
    struct node* current = *headRef;
    int index = 0;

    newNode->data = newData;

    while (current != NULL) {
        if (insertAt == 0 && index == 0) {
            newNode->next = (*headRef);
            (*headRef) = newNode;
            current = *headRef;
            printf("Current's data is now %d at index %d \n\n", current->data, index);
        } else {
            if (index == (insertAt - 1)) {
                printf("I inserted %d at index %d \n", newData, insertAt);
                newNode->next = current->next;
                current->next = newNode;
            }
        }
        current = current->next;
        index++;
    }
}

/*
 * Builds a linked list of a given size.
 */
struct node* BuildList(int numNodes) {
    struct node* head = NULL; // Start with the empty list
    int i;

    for (i = numNodes; i >= 1; i--) {
        Push(&head, i); // Use Push() to add all the data
    }
    return (head);
};

int main(void) {

    struct node* myLinkedList;
    struct node* current;
    int currentIndex = 0;
    int valToInsert = 45;
    int insertIndex = 0;

    myLinkedList = BuildList(5);
    current = myLinkedList;

    InsertNth(&myLinkedList, insertIndex, valToInsert);
    while (current != NULL) {
        printf("The value at index %d is %d \n", currentIndex, current->data);
        currentIndex++;
        current = current->next;
    }

    return 0;
};

输出

Current's data is now 45 at index 0

The value at index 0 is 1
The value at index 1 is 2
The value at index 2 is 3
The value at index 3 is 4
The value at index 4 is 5

上面的输出是当插入新值的索引为零时。这是在索引 1 处插入时的输出。

I inserted 45 at index 1

The value at index 0 is 1
The value at index 1 is 45
The value at index 2 is 2
The value at index 3 is 3
The value at index 4 is 4
The value at index 5 is 5

如您所见，0 不能按预期工作，而 1 可以。我究竟做错了什么？

Answer 1

What am I doing wrong?

您正在设置 current在调用 InsertNth 之前.当您调用 InsertNth插入 0 , myLinkedList会改变，所以 current将指向第二个节点。

移动 current = myLinkedList;到 InsertNth 之后打电话解决问题:

myLinkedList = BuildList(5);
InsertNth(&myLinkedList, insertIndex, valToInsert);
current = myLinkedList;