c - 链接列表未显示正确的数据

Question

我正在学习链接列表，因此决定在这里做一些练习，我试图显示列表中输入的数据。我还添加了一条评论以表达我的理解

typedef struct node {
    int num;
    struct node *nextptr;
}Node;

Node *stnode;
void createNodeList(int n);
void displayList();

这是我创建的节点

void createNodeList(int n) {
    Node *tmp;
    int num = 1;

    //allocate memory address to stnode
    Node *stnode = (Node *)malloc(sizeof(Node));

    if (stnode == NULL) {
        printf("Memory error");
    }
    else {
        printf("Input data for node 1:");
        scanf("%d", &num);

        //declare the stnode num field in struct as user input
        stnode->num = num;
        //declare the stnode address of the next node NULL (to be the last node)
        stnode->nextptr = NULL;
        //define the node name as tmp
        tmp = stnode;

        for (int i = 2; i <= n; i++) {
            //allocate node to fnNode
            Node *fnNode = (Node *)malloc(sizeof(Node));
            if (fnNode == NULL) {
                printf("Memory can not be allocated");
                break;
            }
            else {
                printf("Input data for node %d: ", i);
                scanf("%d", &num);

                //declare the node name fnNode num to store user input
                fnNode->num = num;
                //link the fnNode of nextptr to address null
                fnNode->nextptr = NULL;
                //link tmp node to fnNode
                tmp->nextptr = fnNode;

                tmp = tmp->nextptr;
            }
        }
    }
}

这是为了显示它们

void displayList() {
    Node *tmp;
    if (stnode == NULL) {
        printf("List is empty");
    }
    else {
        tmp = stnode;
        while (tmp != NULL) {
            printf("Data = %d\n", tmp->num);
            tmp = tmp->nextptr;
        }
    }
}

当我输入3个数据后，它应该显示我输入的数据。

但它显示“列表为空”

谢谢=)

Answer 1

Node *stnode = (Node *)malloc(sizeof(Node)); 

这样您就可以隐藏全局变量。这就是为什么您不保留全局变量的任何更改。您所做的只是使用了一个与全局变量 stNode 名称相同的局部变量。

该行应该是

stnode = (Node *)malloc(sizeof(Node));

<子>不要强制转换 malloc 的返回值。应该是

stnode = malloc(sizeof(Node));

或者更清楚

stnode = malloc(sizeof *stnode);

_{If you compile this program with -Wshadow option then you will get warning regarding this shadowing. Enable all compiler warnings. It helps.}