Segfault while printing linked list after stack clear - c

Question

To be more specific, this code is supposed to be a lesser clone of the Unix function dc. The linked list seems to be working fine. If I attempt to use c to clear the memory, add more numbers, then print again with f I get a segfault. It seems to be printing what should be the Null Node in the linked list.
Interaction:
$ ./test
1 2 3
f
3
2
1
c
4 5
f
5
4
0
Segmentation Fault
Here's the code itself:
#include <stdio.h>
#include <stdlib.h>
struct Node{
int val;
struct Node *next;
};
void cons_node(struct Node **head, int num)
{
struct Node *newNode = malloc(sizeof(struct Node));
newNode->val = num;
newNode->next = NULL;
if (*head == NULL){
*head = newNode;
}
else {
newNode->next = *head;
*head = newNode;
}
}
I'm assuming the problem lies here in the display func:
void display_list(struct Node *head)
{
struct Node *current = head;
while(current != NULL)
{
printf("%d\n", current->val);
current = current->next;}
}
void print_top(struct Node *head)
{
printf("%d\n", head->val);
}
or here in the clear func:
void clear_stack(struct Node *head)
{
struct Node *current;
while ((current = head)!= NULL) {
head = head->next;
free(current);
}
}
void vorpal_func(struct Node *head)
{
struct Node *current;
current = head;
free(current);
}
int main(){
int input;
int first = 1;
char quit = 'n';
char inputchar = ' ';
struct Node *head = NULL;
while (quit == 'n'){
if (scanf("%d", &input) == 1){
cons_node(&head, input);
first = 0;
}
else{
inputchar = getchar();
if(first == 1)
printf("List is empty\n");
else{
switch (inputchar){
case 'q':
quit = 'y';
break;
case 'E':
quit = 'y';
break;
case 'f':
display_list(head);
break;
case 'p':
print_top(head);
break;
case 'c':
clear_stack(head);
first = 1;
break;
case 't':
vorpal_func(head);
break;
}
}
}
}
return 0;
}
I've been attempting to figure out the problem for a few hours now. Any tips?

Answer 1

You don't clear your head after calling clear_stack, so when you add your next node, the next pointer is set to something that points into memory that has been freed. Or you could pass a pointer to head to clear_stack if you preferred.
void clear_stack(struct Node **head)
{
while (*head != NULL)
{
Node *current = *head;
*head = current->next;
free(current);
}
}
In passing, cons_node could be written like this
void cons_node(struct Node **head, int num)
{
struct Node *newNode = malloc(sizeof(struct Node));
newNode->val = num;
newNode->next = *head;
*head = newNode;
}