I have a problem with a problem that uses lists - c

Question

I have a problem with this code. I have tried to debug with gdb and Valgrind, But nothing works...
The goal of the code is to create a list, where every string is added only if no existing node with the same string in already part of the list.
This is the code:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
struct node {
char *word;
struct node *next;
};
void print_list(struct node *head) {
while ((head) != NULL) {
printf(" %s -> ", head->word);
head = (head->next);
}
}
// insert a new node in head
void add_n(struct node **head, char *str) {
struct node *new;
new = malloc(sizeof(struct node));
if (new == NULL) {
printf("Not enough memory\n");
exit(EXIT_FAILURE);
}
new->word = str;
new->next = NULL;
if ((*head) == NULL){
(*head) = new;
}
while ((*head)->next != NULL) {
head = &(*head)->next;
}
(*head)->next = new;
}
// check if str is present in the list
int find_string(struct node **head, char *str) {
int found = 0;
while ((*head) != NULL) {
int i = strcmp(str, (*head)->word); //i=0 are the same
if (i == 0) {
found = 1;
return found;
}
head = &((*head)->next);
}
return found;
}
// insert a new string in the list only if is new
void insert(struct node **head, char *str) {
if (find_string(head, str) == 0) {
add_n(head, str);
}
}
void rem_ent(struct node **head, struct node *ent) {
while ((*head) != ent) {
head = &((*head)->next);
}
(*head) = ent->next;
free(ent);
}
void fini_list(struct node **head) {
while ((*head) != NULL) {
rem_ent(head, *head);
head = &((*head)->next);
}
}
int main() {
struct node *head = NULL;
insert(&head, "electric");
print_list(head);
insert(&head, "calcolatori");
print_list(head);
insert(&head, "prova pratica");
print_list(head);
insert(&head, "calcolatori");
print_list(head);
fini_list(&head);
//printf("lunghezza media = %f\n", avg_word_lenght(head));
return 0;
}
Maybe the error might be stupid, but I spent a lot of time debugging without success.

Answer 1

the function fini_list invokes undefined behavior due to the redundant statement
head=&((*head)->next);
because the function rem_ent already set the new value of the pointer head.
void rem_ent(struct node** head, struct node * ent){
while((*head) != ent){
head= &((*head)->next);
}
(*head)= ent->next;
free(ent);
}
Remove the statement
void fini_list(struct node** head){
while((*head) != NULL){
rem_ent(head, *head);
}
}
Also change the function add_n the following way
// insert a new node in head
void add_n(struct node ** head, char* str){
struct node * new;
new = malloc(sizeof(struct node));
if (new == NULL) {
printf("Not enough memory\n");
exit(EXIT_FAILURE);
}
new->word= str;
new->next = NULL;
if ((*head)==NULL){
(*head)=new;
}
else
{
while((*head)->next != NULL){
head = &(*head)->next;}
(*head)->next = new;
}
}
And next time format the code such a way that it would be readable.
In general you should allocate dynamically memory for strings that will be stored in nodes of the list.