C: 无法显示链表值

Question

所以我正在创建一个包含 3 个节点的链表，现在我正在尝试实现一个在 C 中显示列表的函数，代码如下:

struct node *createList(struct node *start)
{
    int i, n, data;


    printf("Enter the number of nodes :  ");
    scanf("%d", &n);

    if (n==0)
        return start;

    printf("Enter the first element to be inserted :  ");

    scanf("%d", &data);

    printf("%d",data);

    start=insertInBeginning(start, data);

    for(i=2; i<=n; i++)
    {
        printf("Enter the next element to be inserted : ");
        scanf("%d", &data);
        insertAtEnd(start, data);
    }
    return start;
}

// end of createList


struct node *insertInBeginning(struct node *start, int data) 
{
    printf("we in begining \n");

    struct node *new_node,*current;

    printf("declared nodes");

    new_node = &data;

    printf("got new_node data \n");

    if(start == NULL) {

        printf("start is null! \n");

        start = new_node;

        current = new_node;

    } else {
        printf("start isn't null!  \n");

        new_node->link=start;

        start=new_node;
    }

}

//end of insertInBeginning


void insertAtEnd(struct node *start, int data)
{
struct node *new_node,*current,*temp;

new_node->info = data;
if(start == NULL)
 {

start= new_node;
current= new_node;

} else 
{
    temp = start;

    while(temp->link!=NULL) {
        temp =  temp->link;
    }
    temp -> link = new_node;
}


}

// end of insertAtEnd



void displayList(struct node *start)
{

    printf("we in displaylist");
    struct node *temp;

    temp = start->link;
    printf("temp has start values?");

    if(temp = NULL)
    {
    printf("we null now \n");
    } else {
    printf("we NOT null \n" );
    while(temp!=NULL) 
    {
    printf("%d \n",temp->info);
    temp = temp->link;
    }
}
}

我遇到的问题是，在显示函数中，循环完成了，但它没有打印任何值，但是我知道 temp 不为 NULL，所以它显示的东西，只是不是我想要的，是有办法解决这个问题吗？

Answer 1

这里有两个大问题:首先，(正如 Martin James 指出的)，insertInBeginning() 例程没有返回，因此 start 设置为某个未定义的值。您还面临一个巨大的问题，即您只是将 int data 转换为 node *。您必须为新节点 malloc() 内存并向其中写入数据。 (然后返回它)您的 insertAtEnd() 例程中也有同样的问题——您必须 malloc() 内存来保存新节点。

static struct node *
insertAtStart (struct node *start, int data)
{
    struct node *new;

    new = malloc(sizeof(*new));
    if (new == NULL) {
        perror("malloc");
        exit(1);
    }

   new->value = data;
   new->next = start;
   return new;
}

static struct node *
insertAtEnd (struct node *start, int data)
{
    struct node *cur, *new;

    // create the node * we will be adding.  (This really ought to have been done
    // in the calling routine, so the same code would be used to create the node
    // entry and to store the value.  Note a big issue with this simple a struct,
    // but more complex structs really ought to only be created in one place, so
    // when they change, you won't have bugs where you forget to change one of 
    // the creation locations)
    new = malloc(sizeof(*new));
    if (new == NULL) {
        perror("malloc");
        exit(1);
    }
    new->value = data;
    new->link = NULL;

    // if this is going to be the only entry in the list, just return that it 
    // is the new start
    if (start == NULL) 
        return new;

    // find the last entry
    for (cur = start ; cur->link != NULL ; cur = cur->link)
        ;
    cur->link = new;
    return start;
}

您确实想打开编译器警告 - 让编译器告诉您此类错误可以节省大量时间。如果您使用的是 gcc，请将 -Wall -Werror 添加到编译命令中(如果您使用的是不同的编译器，则需要阅读手册页)。

(您还可以打开其他 gcc 警告，但是 -Wall 为您提供了很多有用的警告。如果您想打开更多警告，可以阅读手册页来查找所有您想要的警告)