adding item to the end of linked list segfault - c

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;
}
I am trying to add vehicle to end of the list but it gives me Segmentation fault after second scanf, I dont know is my mistake in loops or in scanf. My struct is like:
struct vehicle {
char regnro[7];
char *model;
struct vehicle *next;
};

Answer 1

Firstly as pointed by other in comments model is pointer member of structure & its not initialzed. When you do scanf("%s", newcar->model); it gives seg. fault. So first allocate memory for it dynamically. For e.g
newcar->model = malloc(SIZE); /* define SIZE */
Secondly, you are passing just normal struct vehicle variable to add_vehicle() method So whatever changes are done with v in add_vehicle() won't affect in main() method. Instead pass the address of struct vehicle variable to add_vehicle() method, in that case you no need to return the struct variable as it will be call by reference. for e.g
main() method call looks like
struct vehicle *head = NULL;
add_vehicle(&head);
And definition of add_vehicle() looks like
void add_vehicle(struct vehicle **v){
/* some code */
}
Here is the sample code you may want
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;
}