Finally I have a valid reason to learn about memory management. It was also hella weird when encountering it.

  • da_cow (she/her)@feddit.orgOP
    5·
    3 days ago

    That’s the funny thing. I had a (yet) very basic Programm and did not care at all about memory management. When I did some testing I realised, that for some reason when I printed string 1 I also got characters from string 2.

    • henfredemars@infosec.pubEnglish
      8·
      3 days ago

      That sounds like it could be memory corruption. That should not happen because every string should be separated by a null terminator.

      • da_cow (she/her)@feddit.orgOP
        8·
        3 days ago

        This is the code I used:

        #include <stdio.h>
#include <string.h>

#define MAX_ACCOUNTS 255

typedef struct
{
    unsigned int id;
    char account_creation_date [10];
    char first_name [255];
    char last_name [255];
    char country_code [2];
    unsigned int iban;
    char password [255];
    double balance;
} account;

account accounts_db[MAX_ACCOUNTS];
unsigned int accounts_created = 0;

account get_account_id (unsigned int id)
{
    int i = 0;
    while(i < MAX_ACCOUNTS)
    {
        if(accounts_db[i].id == id)
        {
            return accounts_db[i];
        }
        i++;
    }
    account account;
    account.id = -1;
    return account;
}

void create_account(char first_name [255], char last_name [255], char password [255], char country_code [2])
{
    account new_account;
    new_account.id = accounts_created;
    strcpy(new_account.first_name, first_name);
    strcpy(new_account.last_name, last_name);
    strcpy(new_account.password, password);
    strcpy(new_account.country_code, country_code);
    strcpy(new_account.account_creation_date, "");
    new_account.balance = 0.0;
    new_account.iban = 0;
    accounts_db[accounts_created] = new_account;
    accounts_created++;
}

int main()
{
    char first_name [255]  = "Max";
    char last_name [255] = "Mustermann";
    char country_code [2] = "DE";
    char password [255]= "password";
    create_account(first_name, last_name, password,country_code);
    account account = get_account_id(0);
    printf("Name: %s %s \n", account.first_name, account.last_name);
    printf("Account creation date: %s\n", account.account_creation_date);
    printf("IBAN: %s %d", account.country_code, account.iban);
}```

When you run it you can see, that behind the country code of the IBAN you get the first two letters of the surename
        • LedgeDrop@lemmy.zip
          14·
          3 days ago

          Without getting too critical of your code (congrats BTW), never use strcpy instead use strlcpy.

          strcpy will happily allow you to create buffer overflows (a common challenge with C) which will cause your application to crash.

          You’ll find more details here.

          Good luck!

          • da_cow (she/her)@feddit.orgOP
            7·
            3 days ago

            Thanks, I did not knew this. I always appreciate constructive criticism. I am quite new to C so theres a shit ton of stuff I have never done or dont even know about.

          • ozymandias117@lemmy.worldEnglish
            5·
            3 days ago

            And understand when you can use them…

            I’ve seen too much code following this advice blindly that just does something like

            strncpy(dst, src, strlen(src))

        • da_cow (she/her)@feddit.orgOP
          8·
          3 days ago

          I found the mistake. Since the country code char array only has a size of 2 it overwrites the \0 char causing the memory to leak.

          • silasmariner@programming.dev
            16·
            3 days ago

            Usually what’s meant by a memory leak is memory that’s allocated but never freed. Writing outside of array allocation would usually be considered an overflow. Which sounds kinda similar but is not the same.