Save structs in a file - c

Question

I'm doing a program to save a list of contacts in a file whit structs. I've tried a lot of things but when I try go read the file to the program, it doesn't read anything.
This is my program without opening files and saving to files:
#include <stdio.h>
#include <stdlib.h>
struct agenda {
int idContacte;
char name[50];
struct agenda *nextContacte;
};
struct agenda *pAgenda;
struct agenda *pFirst = NULL;
struct agenda *pIndex;
void insert();
void show();
int main()
{
//Menu
int opc;
while(1){
printf("1.Insert Contact.\n");
printf("2.Show Contacts.\n");
printf("3.Exit\n");
scanf("%d", &opc);
switch(opc){
case 1:
insert();
break;
case 2:
show();
break;
case 3:
return 0;
}
}
}
void insert(){
pAgenda = (struct agenda *)malloc(sizeof(struct agenda));
printf("Insert ID: ");
scanf("%d", &pAgenda->idContacte);
printf("Insert the name: ");
scanf("%s", pAgenda->name);
printf("\n");
if (pFirst==NULL || pAgenda->idContacte < pFirst->idContacte)
{
pAgenda->nextContacte=pFirst;
pFirst=pAgenda;
}
else if (pAgenda->idContacte > pFirst->idContacte){
pIndex=pFirst;
while(pIndex->nextContacte && pIndex->nextContacte->idContacte < pAgenda->idContacte)
{
pIndex = pIndex->nextContacte;
}
pAgenda->nextContacte = pIndex->nextContacte;
pIndex->nextContacte = pAgenda;
}
}
void show(){
pIndex = pFirst;
while(pIndex && pIndex->idContacte <= 100) {
printf("\nID: %d", pIndex->idContacte);
printf("\nNAME: %s", pIndex->name);
printf("\n\n");
pIndex = pIndex->nextContacte;
}
}
Can you help me how can I get contact at start of the program from a file, and then when insert a contact, rewrite the file and insert all the contacts again in the file?

Answer 1

When you end your program you should do the following
int save_list(struct agenda *head) {
FILE *save = fopen("file.name", "wb");
if(!save) return -1;
while(head) {
fwrite(head, sizeof *head - sizeof head, 1, save);
head = head->nextContacte;
}
fclose(save);
/* Somebody would free list memory after this function execution */
return 0;
}
At the start of your program you should do the following
struct agenda *restore_list() {
FILE *restore= fopen("file.name", "rb");
struct agenda *head = NULL;
struct agenda *cur = head;
struct agenda temp;
if(!restore) return head;
while( fwrite(&temp, sizeof temp - sizeof head, 1, save) == 1) {
struct agenda *node = malloc( sizeof(struct agenda) );
if(NULL == node) {
/* Handle out of memory error here, free list */
return NULL;
}
*node = temp;
node->nextContacte = NULL;
if(head) {
cur->nextContacte = node;
cur = node;
} else {
/* First node */
head = cur = node;
}
}
fclose(restore);
return head;
}