Question

I need to do an assignment for a class I’m taking.
It’s a simple phonebook app in C, and i’m having a little trouble with it since I need to use some new stuff in the program and the deadline is pretty tight.

I looked around and found some answers, but a new one came up every time. 🙂

This is my (simplified) program:

typedef struct record
{
    char fname[31];
    char lname[31];
    char tel[21];
    struct record *next;
} record;


record *new_entry(record *first, char *fname, char *lname, char *tel)
{
    record *new;
    new=(record*) malloc(sizeof(record));
    strcpy(new->fname, fname);
    strcpy(new->lname, lname);
    strcpy(new->tel, tel);
    new->next=first;
}


void fileopen (char *db_file)
{
    FILE *fp;  

    fp=fopen(db_file, "rb");
    if (fp==NULL) 
    {
        fp=fopen(db_file, "wb");
        fclose(fp);
        fp=fopen(db_file, "r+b");
    }
}



int main
{
 char db[51];
 record *next = NULL;

 printf("File:           "); scanf("%s, db);
 fileopen(db);
 printf("First name:     "); scanf("%s", fname);
 printf("Last name:      "); scanf("%s", lname);
 printf("Phone number:   "); scanf("%s", tel);
 first=new_entry(*first, fname, lname, tel);
}

I left out the unessential parts.
Now I know it’s not much, but my class leader said I should use binary files to store and restore the data. But I got really confused if how am I supposed to use fread and fwrite.

---

Thanks so much for the solution! I think I start to understand the concept.
The program now stores the data (At least I think it does, because the file keeps growing as I add more data.)
When starting a fresh binary file, the program correctly displays the data when requested, but if I close it, and reopen the same file, nothing happens when it tries to list the contacts.

Here’s the (simplified again, i have 10 details in one record in the actual assignment) open function:

record *open (char *db_file, record start)
{
  FILE *fp
  record *temp = start;
  fp=fopen(db_file, "rb");
  while (fread(temp, sizeof(rekord), 1, fp)>0) 
    {
        fread(temp->fname, sizeof temp->fname, 1, fp);
        fread(temp->lname, sizeof temp->lname, 1, fp);
        fread(temp->tel, sizeof temp->tel, 1, fp);
    temp=temp->next;
    }
  fclose(fp);
  return temp;
}

And in main(), I use:

start=open(db, start);

The declaration part:

record *start=NULL;

Thanks again if someone replies.

Answer 1

To write your linked list to a file, you can run through the list, and write your structure.

#include <stdio.h>

record *it = first;

while (it != NULL) {
    fwrite (it->fname, sizeof it->name, 1, stream);
    fwrite (it->lname, sizeof it->lname, 1, stream);
    fwrite (it->tel, sizeof it->tel, 1, stream);
    it = it->next;
}

stream is a file you can open with wb mode in fopen.