Segmentation fault while iterating through list - c

Question

I'm getting segmentation fault when trying to access current_nap->next (sometimes even on current->value->napok but that's rare). I don't get why this happens because I can iterate through NapList with the functions in its header without any problem. Could you help me, please?
Here is my code:
void saveToFile()
{
int g;
g = open("save.dat", O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
JelentkezesList *current = jelentkezesek;
char line[] = "";
while (current != NULL)
{
printf("eddig ok\n");
strncpy(line, "", sizeof(line));
printf("eddig ok2\n");
strcat(line, "{");
strcat(line, current->value->nev);
strcat(line, ";");
strcat(line, current->value->cim);
strcat(line, ";");
printf("eddig ok3\n");
NapList *current_nap = current->value->napok;
printf("eddig ok4\n");
while (current_nap != NULL)
{
printf("eddig ok5\n");
if (current_nap->value == HETFO)
{
strcat(line, "0");
printf("hetfo\n");
}
else if (current_nap->value == KEDD)
{
strcat(line, "1");
printf("kedd\n");
}
else if (current_nap->value == SZERDA)
{
strcat(line, "2");
printf("szerda\n");
}
else if (current_nap->value == CSUTORTOK)
{
strcat(line, "3");
printf("csutortok\n");
}
else if (current_nap->value == PENTEK)
{
strcat(line, "4");
printf("pentek\n");
}
else if (current_nap->value == SZOMBAT)
{
strcat(line, "5");
printf("szombat\n");
}
else if (current_nap->value == VASARNAP)
{
strcat(line, "6");
printf("vasarnap\n");
}
printf("eddig ok5.1\n");
//if (current_nap->next != NULL)
//{
strcat(line, ",");
//}
printf("eddig ok6\n");
current_nap = current_nap->next;
printf("eddig ok7\n");
}
strcat(line, "}\n");
if (write(g, line, sizeof(line)) != sizeof(line))
{
printf("Hiba a mentés során!");
exit(1);
}
printf("eddig ok8\n");
current = current->next;
printf("eddig ok9\n");
}
close(g);
printf("%s", "Sikeres mentés!");
}
Here are my headers:
JelentkezesList
#include "string_utils.h"
#include "jelentkezes.h"
#include "nap_list.h"
#ifndef JELENTKEZES_LIST_H
#define JELENTKEZES_LIST_H
typedef struct jelentkezes_node
{
Jelentkezes *value;
struct jelentkezes_node *next;
} JelentkezesList;
void printJelentkezesList(JelentkezesList *head)
{
JelentkezesList *current = head;
while (current != NULL)
{
printf("\n");
printJelentkezes(current->value);
current = current->next;
}
}
void printJelentkezesListForDay(JelentkezesList *head, Nap nap)
{
JelentkezesList *current = head;
while (current != NULL)
{
if (containsNap(current->value->napok, nap))
{
printf("\n");
printJelentkezes(current->value);
}
current = current->next;
}
}
void addToJelentkezesList(JelentkezesList **list, Jelentkezes *value)
{
JelentkezesList *current = *list;
if (current == NULL)
{
current = (JelentkezesList *)malloc(sizeof(JelentkezesList));
Jelentkezes *j = value;
j->azonosito = 0;
current->value = j;
current->next = NULL;
*list = current;
}
else
{
while (current->next != NULL)
{
current = current->next;
}
current->next = (JelentkezesList *)malloc(sizeof(JelentkezesList));
Jelentkezes *j = value;
j->azonosito = current->value->azonosito + 1;
current->next->value = j;
current->next->next = NULL;
}
}
Jelentkezes *findJelentkezes(JelentkezesList *list, int id)
{
Jelentkezes *result = NULL;
JelentkezesList *current = list;
while (current != NULL && result == NULL)
{
if (current->value->azonosito == id)
{
result = current->value;
}
current = current->next;
}
return result;
}
void deleteJelentkezes(JelentkezesList **list, Jelentkezes *j)
{
JelentkezesList *current = *list;
if (current->value->azonosito == j->azonosito)
{
*list = current->next;
free(current);
return;
}
while (current->next->value->azonosito != j->azonosito)
{
current = current->next;
}
JelentkezesList *toDelete = current->next;
current->next = current->next->next;
free(toDelete);
*list = current;
}
JelentkezesList *createJelentkezesList()
{
JelentkezesList *jelentkezes_head = NULL;
return jelentkezes_head;
}
#endif
Jelentkezes
#include "string_utils.h"
#include "nap.h"
#include "nap_list.h"
#include <stdio.h>
#include <string.h>
#ifndef JELENTKEZES_H
#define JELENTKEZES_H
typedef struct
{
int azonosito;
String nev;
String cim;
NapList *napok;
} Jelentkezes;
Jelentkezes *createJelentkezes(String *nev, String *cim, NapList *napok)
{
Jelentkezes *j = (Jelentkezes *)malloc(sizeof(Jelentkezes));
j->azonosito = -1;
j->nev = *nev;
j->cim = *cim;
j->napok = napok;
return j;
}
void printJelentkezes(Jelentkezes *j)
{
printf("Azonosító: %d\n", j->azonosito);
printf("Név: %s, Cím: %s\n", j->nev, j->cim);
printf("Munkavállalás napjai: ");
printNapList(j->napok);
}
#endif
NapList
#include "string_utils.h"
#include "nap.h"
#include <stdbool.h>
#ifndef NAP_LIST_H
#define NAP_LIST_H
typedef struct nap_node
{
Nap value;
struct nap_node *next;
} NapList;
void printNapList(NapList *head)
{
NapList *current = head;
while (current != NULL)
{
if (current->value == HETFO)
{
printf("hétfő");
}
else if (current->value == KEDD)
{
printf("kedd");
}
else if (current->value == SZERDA)
{
printf("szerda");
}
else if (current->value == CSUTORTOK)
{
printf("csütörtök");
}
else if (current->value == PENTEK)
{
printf("péntek");
}
else if (current->value == SZOMBAT)
{
printf("szombat");
}
else if (current->value == VASARNAP)
{
printf("vasárnap");
}
if (current->next != NULL)
{
printf(", ");
}
current = current->next;
}
printf("\n");
}
void addToNapList(NapList **list, Nap value)
{
NapList *current = *list;
if (current == NULL)
{
current = (NapList *)malloc(sizeof(NapList));
current->value = value;
current->next = NULL;
*list = current;
}
else
{
while (current->next != NULL)
{
current = current->next;
}
current->next = (NapList *)malloc(sizeof(NapList));
current->next->value = value;
current->next->next = NULL;
}
}
bool containsNap(NapList *nl, Nap nap)
{
NapList *current = nl;
while (current != NULL)
{
if (current->value == nap)
return true;
current = current->next;
}
return false;
}
NapList *createNapList()
{
NapList *nap_head = NULL;
return nap_head;
}
#endif