Store data from files in array of structure C

Question

So I'm stuck in this piece of code that I'm writing and I want to save data that I receive from a binary file and save it in a array of structure I already tried something but I can't get any good results.

#define MAX_ACCOUNTS 5
#define COUNTER 0
typedef struct t_account {
    int id;
    char name[50];
    char provider[40];
    char org[40];
    char domain[50];
    float balance;
} t_account;


    t_account account[MAX_ACCOUNTS];
    char *item;
    FILE *file_accounts;
    char string[0];
    int i = COUNTER;

    file_accounts = fopen("../accounts.dat", "rb");

    if (file_accounts == NULL) {
        printf("Error, %s\n", strerror(errno));
        exit(1);
    } else {
        printf("Testing fread() function: \n\n");
        //fread(string, sizeof(string), MAX_ACCOUNTS, file_accounts );
        while(fgets(string, sizeof(struct t_account), file_accounts )){
            printf("%s\n", string);
            item = strtok(string, ";");

            printf("ID: %i\n", strtol(item,NULL,10));
            item = strtok(NULL, ";");

            printf("Name: %s\n", item);
            item = strtok(NULL, ";");

            printf("Provider: %s\n", item);
            item = strtok(NULL, ";");

            printf("ORG: %s\n", item);
            item = strtok(NULL, ";");

            printf("Domain: %s\n", item);
            item = strtok(NULL, ";");

            printf("Balance: %.2f Eur\n", strtof(item, NULL));
            i++;
        }
    }


    fclose(ficheiro_contas);

I already tried to save the data inside the while loop like this but for each field in the structure

account[i].id = atoi(item);

but the program crashes in the line that I do that piece of code to "save" the array.

strtok(string returns a pointer into string. It does not return a copy. — Paul Ogilvie
– Paul Ogilvie, Commented Jan 19, 2020 at 14:48
Yes I know, but in that case it returns the first string before the ";" so it I convert it to an integer. — João Neves
– João Neves, Commented Jan 19, 2020 at 14:50
char string[0]; is a string of zero length. I certainly is not sizeof(struct t_account). And it does not make sense to read sizeof(struct t_account) chars from the file. — Paul Ogilvie
– Paul Ogilvie, Commented Jan 19, 2020 at 14:50
What about char string[512];? And then read the documentation of fgets — Paul Ogilvie
– Paul Ogilvie, Commented Jan 19, 2020 at 14:52

Paul Ogilvie · Accepted Answer · 2020-01-19 15:00:03Z

1

Your main problem is that your string is zero size, yet you try to read sizeof(struct t_account) bytes into it. That overwrites other data, causing undefined behavior and your crash.

Try:

   char string[512];
   int k= 0;
   while(fgets(string, sizeof(string), file_accounts )){
        item = strtok(string, ";");
        strcpy(account[k].name, item);
        //
        // etc...
        //
        k++;
   }

answered Jan 19, 2020 at 15:00

Paul Ogilvie

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6 Comments

João Neves Over a year ago

Okay I understand it now, please get in the chat so we can talk better.

João Neves Over a year ago

it is now working... finally, how can I add \n inside the .dat file after one string behind ";"?

João Neves Over a year ago

like this: "1;Conta1_Amazon\n;AWS\n;IPLeiria\n;ipleiria.pt\n;1213.65;"

Paul Ogilvie Over a year ago

From gets documentation: "The line [gets reads] consists of all characters up to and including the first newline character ('\n'). gets then replaces the newline character with a null character ('\0')". But if there are no newline characters int the file, then that's a whole different problem.

João Neves Over a year ago

it only saves in the first position of the array

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