c - 将项目添加到链表的末尾 segfault

Question

struct vehicle *add_vehicle(struct vehicle *v){

    struct vehicle *newcar = (struct vehicle*)malloc(sizeof(struct 
    vehicle));
    scanf("%s", newcar->regnro);
    scanf("%s", newcar->model);
    newcar->next = NULL;
   if(v->next == NULL){
      v->next =newcar;
  }
   else{
       struct vehicle *current = v;
       while(current->next != NULL){
           current = current->next;
           }
         current->next = newcar;
         }
 return v; 
       }

我正在尝试将车辆添加到列表末尾，但在第二次 scanf 后它给了我段错误，我不知道是我在循环中还是在 scanf 中犯了错误。我的结构是这样的:

    struct vehicle {
    char regnro[7];
    char *model;
    struct vehicle *next;
};

Answer 1

首先，正如评论中其他人指出的那样 model是结构体的指针成员且未初始化。当你这样做时scanf("%s", newcar->model);它给出了段。过错。所以首先为其动态分配内存。例如

newcar->model = malloc(SIZE); /* define SIZE */

其次，你的成绩很正常struct vehicle变量为add_vehicle()方法所以无论做什么改变都是用 v 完成的在add_vehicle()不会影响main()方法。相反pass the address的struct vehicle变量为add_vehicle()方法，在这种情况下，您不需要返回结构变量，因为它将通过引用调用。例如 main()方法调用看起来像

struct vehicle *head = NULL;
add_vehicle(&head);

以及 add_vehicle() 的定义看起来像

void add_vehicle(struct vehicle **v){
    /* some code */
}

这是您可能需要的示例代码

void add_vehicle(struct vehicle **v){

        struct vehicle *newcar = malloc(sizeof(struct vehicle));/* no need to type cast the result of malloc */
        scanf("%s", newcar->regnro);
        /* model is pointer member of dtruct, you need to do malloc for it */
        newcar->model = malloc(SIZE)); /*define the size value */
        scanf("%s", newcar->model);

        newcar->next = NULL;
        if((*v) == NULL){ /* first node */
                newcar->next = *v; /* newnode next make it to head node */
                (*v) = newcar; /*update the head node and */
                return;
        }
        else{
                struct vehicle *current = *v;
                while(current->next != NULL){ /* move temp to the end node of list  */
                        current = current->next;
                }
                current->next = newcar;/* add the new_node at last of the list */
        }
}
void print_info(struct vehicle *temp) {
        while(temp) {
                printf("%s %s\n",temp->regnro,temp->model);
                temp= temp->next;
        }
}
int main(void) {
        struct vehicle *head = NULL;            
        add_vehicle(&head); /* pass the address of head */
        print_info(head);
        return 0;
}