创建链接列表，不传回主

Question

因此，我在一个单独的函数中创建链接列表，并且当我打印出函数中的链接列表时，似乎一切正常。然而;当我转到main并尝试使用printf访问链接列表时，我得到了一个分段错误，我很困惑，为什么。

void createLL(struct node* head, struct node* curr, char ch, int number){ 
//lowest digit is the head 
    while (((scanf(" %c",&ch)) >= 0)){ 
     curr = (struct node*)malloc(sizeof(struct node*)); //allocate space 
     number = ch - '0' ; //convert char to number 
     curr->data = number; 
     curr->next = head; 
     head = curr; 
    } 
    curr = head; 
    //troubleshoot 
    while(curr){ 
     printf("%d\n",curr->data); 
     curr = curr->next; 
    } 
    curr = head; 
    printf("%d\n",curr->data); 
} 

int main(){ 
    //initials 
    int i, number; 
    char ch; 
    //node pointers 
    struct node* headOne = NULL; 
    struct node* currOne = NULL; 
    struct node* headTwo = NULL; 
    struct node* currTwo = NULL; 
    //create linked list 
    createLL(headOne,currOne, ch, number); 
    printf("%d\n",currOne->data); 
    createLL(headTwo,currTwo, ch, number); 
    printf("%d\n",currTwo->data); 

Answer 1

在C函数中按值传递所有参数。所以如果你想在函数中改变一个变量，你需要传递该变量的地址并在函数中解引用参数。

另外，您没有为节点分配适量的空间。你想sizeof(struct node)，而不是sizeof(struct node *)。

void createLL(struct node **head, struct node **curr, char ch, int number){ 
//lowest digit is the head 
    while (((scanf(" %c",&ch)) >= 0)){ 
     // don't cast the return value of malloc 
     *curr = malloc(sizeof(struct node)); //allocate space 
     number = ch - '0' ; //convert char to number 
     (*curr)->data = number; 
     (*curr)->next = *head; 
     *head = *curr; 
    } 
    *curr = *head; 
    //troubleshoot 
    while(*curr){ 
     printf("%d\n",(*curr)->data); 
     *curr = (*curr)->next; 
    } 
    *curr = *head; 
    printf("%d\n",(*curr)->data); 
} 


int main(){ 
    //initials 
    int i, number; 
    char ch; 
    //node pointers 
    struct node* headOne = NULL; 
    struct node* currOne = NULL; 
    struct node* headTwo = NULL; 
    struct node* currTwo = NULL; 
    //create linked list 
    createLL(&headOne,&currOne, ch, number); 
    printf("%d\n",currOne->data); 
    createLL(&headTwo,&currTwo, ch, number); 
    printf("%d\n",currTwo->data); 
}