Create an address book using a linked list - c

Question

I opened a thread yesterday asking about how I should proceed. Here is what I've got so far (sorry for the language, the program will be in Albanian but I'm sure you are getting the point).
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
void regjistrim();
void kerkim();
void modifikim();
void fshirje();
void rradhitje();
void display();
void load();
#define EMRI 50
#define MBIEMRI 50
#define ID 20
#define TEL 20
#define EMAIL 25
typedef struct node
{
char emri[EMRI];
char mbiemri[MBIEMRI];
char id[ID];
char tel[TEL];
char email[EMAIL];
struct node* next;
} node;
FILE* addressbook;
node* mynode;
node* curr;
int main(void)
{
char input[2];
int choice;
load();
printf("----------------ADDRESS BOOK----------------");
printf("\n\n\t1 - Regjistrimi i ri\n");
printf("\n\t2 - Kerkim\n");
printf("\n\t3 - Modifikim\n");
printf("\n\t4 - Fshirje\n");
printf("\n\t5 - Rradhitje\n");
printf("\n\t6 - Afishim i address book\n");
printf("\n\t0 - Exit\n");
fgets(input, 4, stdin);
sscanf(input, "%d", &choice);
while (choice < 0 || choice > 6)
{
printf("\nShtypni nje numer nga 0 - 6: \n");
fgets(input, 4, stdin);
sscanf(input, "%d", &choice);
}
switch (choice)
{
case 1:
regjistrim();
break;
case 2:
kerkim();
break;
case 3:
modifikim();
break;
case 4:
fshirje();
break;
case 5:
rradhitje();
break;
case 6:
display();
break;
case 0:
exit(0);
break;
}
return 0;
}
void load()
{
addressbook = fopen("Addressbook.txt", "r");
if (addressbook == NULL)
printf("Could not open file.");
node* mynode = malloc(sizeof(node));
while (fscanf(addressbook, "%s %s %s %s %s", mynode->emri, mynode->mbiemri, mynode->id, mynode->tel, mynode->email) != EOF)
{
node* mynode = malloc(sizeof(node));
mynode = mynode->next;
}
mynode = curr;
}
//Regjistron nje qytetar ne addressbook
void regjistrim()
{
char input[2];
char answer;
do
{
node* newnode = malloc(sizeof(node));
curr->next = newnode;
addressbook = fopen("Addressbook.txt", "a+");
printf("\nShtypni emrin: ");
fgets(newnode->emri, EMRI, stdin);
printf("\nShtypni mbiemrin: ");
fgets(newnode->mbiemri, MBIEMRI, stdin);
printf("\nShtypni ID-in: ");
fgets(newnode->id, ID, stdin);
printf("\nShtypni nr. telefoni: ");
fgets(newnode->tel, TEL, stdin);
printf("\nShtypni email-in: ");
fgets(newnode->email, EMAIL, stdin);
fprintf(addressbook, "Emri: %sMbiemri: %sID: %sNr. telefoni: %sEmail: %s\n", newnode->emri, newnode->mbiemri, newnode->id, newnode->tel, newnode->email);
fclose(addressbook);
printf("\nShtypni y/Y neqoftese doni te regjistroni person tjeter: ");
fgets(input, 50, stdin);
sscanf(input, "%c", &answer);
curr = newnode;
}
while(answer == 'y' || answer == 'Y');
}
void kerkim()
{
//TODO
}
void modifikim()
{
//TODO
}
void fshirje()
{
//TODO
}
void rradhitje()
{
//TODO
}
void display()
{
//TODO
}
Currently I'm getting a segfault at this point: while (fscanf(addressbook, "%s %s %s %s %s", mynode->emri, mynode->mbiemri, mynode->id, mynode->tel, mynode->email) != EOF)
I am mainly concerned about the load() function which will load any entries to the linked list, if there are any, before the user does any action.
Thank you in advance.

Answer 1

I recommend you check out existing implementations of linked lists. Add helper functions for inserting nodes, appending nodes, deleting nodes, and those sorts of things. Once you have a working implementation for the lists themselves, you will have an easier time writing code that takes advantage of the linked list data structure.
Consider changing your node structure to include a pointer to the actual data and a pointer to the next node (instead of actually having the data in the struct itself). Better practice this way. You could even expand your linked list implementation to support any data type by using void pointers as "generic" pointers.
A segmentation fault with linked lists usually indicates that you are dereferencing a NULL pointer somewhere in your code (but is not the case all of the time!). Ensure that you are not referencing nodes that have been deleted or nodes that have not been allocated yet.
If you are satisfied with your current implementation, step through the code with gdb and set a breakpoint where the program is segfaulting. You should not have a hard time tracking down where the bug is.

Answer 2

If you want to create a linked list try doing this
Replace this code
node* mynode = malloc(sizeof(node));
while (fscanf(addressbook, "%s %s %s %s %s", mynode->emri, mynode->mbiemri, mynode->id, mynode->tel, mynode->email) == 5)
{
node* mynode = malloc(sizeof(node));
mynode = mynode->next;
}
mynode = curr;
with this
node* mynodeLocal = malloc(sizeof(node));
node *secondLastNode;
while (fscanf(addressbook, "%s %s %s %s %s", mynodeLocal->emri, mynodeLocal->mbiemri, mynodeLocal->id, mynodeLocal->tel, mynodeLocal->email) != EOF)
{
secondLastNode = mynodeLocal;
mynodeLocal->next = malloc(sizeof(node));
mynodeLocal = mynodeLocal->next;
mynodeLocal->next = NULL;
}
secondeLastNode->next = NULL;
mynode = curr;//Change this line according to your requirement.