链表实现分段错误

Question

I have done basic implementation of Linked List but its giving Segmentation fault on uncommenting the commented lines otherwise its working fine. I am not able to understand why its giving the error. Please give me some help

void insert(Node **head, Symbol sym) {
    Node *temp, *p = *head;;
    Symbol a = sym;
    temp = (Node *)malloc(sizeof(Node));
    temp->value = a;
    temp->next = NULL;

    if (p == NULL)
        *head = temp;
    else {
        while (p->next != NULL)
            p = p->next;
        p->next = temp;
    }
}

void printList(Node *head) {
    Node *p = head;
    if(p == NULL) return;
    while (p != NULL) {
        printf("%d ", p->value);
        p = p->next;
    }
    printf("\n");
}
int main() {
    Node *List, *list2;
    insert(&List, 0);
    insert(&List, 1);

    //insert(&list2, 2);
    //insert(&list2, 3);

    printList(List);
    return 0;
}

Answer 1

You did not initialize initial pointers to nodes

Node *List, *list2;

Write

Node *List = NULL, *list2 = NULL;

Take into account that variable list2 is not used in the program you showed.

The other way to write function insert is the following

void insert( Node **head, Symbol sym ) 
{
    Node *temp = malloc( sizeof( Node ) );

    if ( temp != NULL )
    {
        temp->value = sym;
        temp->next  = NULL;

        while ( *head ) head = &( *head )->next;
        *head = temp;
    }
}