c - 添加到 C 中链表的开头

Question

我知道如何添加到链接列表的末尾，但我不明白为什么这个添加到链接列表开头的代码不起作用。在这个特定问题的备忘录中，他们使用了指向 head 变量的双指针，但我不太明白为什么这是必要的。这是不起作用的代码:

void addtobeginning( struct node *head, int userdata)
{
    struct node *newnode;
    struct node *p;
    p = head;

    newnode = malloc(sizeof(struct node));
    newnode->data = userdata;
   newnode->link = p;
   head = newnode;




}

Answer 1

也许这可以帮助您完成相同的任务

struct Student* Add_Student()
{
    Student *p;
    p = (Student*)malloc(sizeof(Student));
    printf("enter name: ");
    scanf("%s", p->name);

    printf("enter ID: ");
    scanf("%d", &p->id);

    printf("enter address: ");
    scanf("%s", p->address);

    printf("enter avg: ");
    scanf("%f", &p->avg);

    p->Next = NULL;

    return p;
}

if (head == NULL)
                 head = s;
            else
            {
                p = head;
                head = s;
                head -> Next = p;
            }