Question

This is my code:

  void get_pass(char *p);

int main(){

    char *host, *user, *pass;

    host = malloc(64); /* spazio per max 64 caratteri */
    if(!host) abort(); /* se malloc ritorna NULL allora termino l'esecuzione */
    host[63] = '\0';   /* evitare un tipo di buffer overflow impostando l'ultimo byte come NUL byte */

    user = malloc(64);
    if(!user) abort();
    user[63] = '\0';

    pass = malloc(64);
    if(!pass) abort();
    pass[63] = '\0';

    /* Immissione di hostname, username e password; controllo inoltre i 'return code' dei vari fscanf e, se non sono 0, esco */
    fprintf(stdout,"--> Inserisci <hostname>: ");
    if(fscanf(stdin, "%63s", host) == EOF){
        fprintf(stdout, "\nErrore, impossibile leggere i dati\n");
        exit(EXIT_FAILURE);
    }
    fprintf(stdout,"\n--> Inserisci <username>: ");
    if(fscanf(stdin, "%63s", user) == EOF){
        fprintf(stdout, "\nErrore, impossibile leggere i dati\n");
        exit(EXIT_FAILURE);
    };
    fprintf(stdout, "\n--> Inserisci <password>: ");
    get_pass(pass);

    /* Stampo a video le informazioni immesse */
    fprintf(stdout, "\n\nHost: %s\nUser: %s\nPass: %s\n\n", host,user,pass);

    /* Azzero il buffer della password e libero la memoria occupata */
    memset(pass,0,(strlen(pass)+1));
    free(host);
    free(user);
    free(pass);

    return EXIT_SUCCESS;
}

void get_pass(char *p){
    /* Grazie a termios.h posso disabilitare l'echoing del terminale (password nascosta) */
    struct termios term, term_orig;
    tcgetattr(STDIN_FILENO, &term);
        term_orig = term;
        term.c_lflag &= ~ECHO;
        tcsetattr(STDIN_FILENO, TCSANOW, &term);
        /* Leggo la password e controllo il 'return code' di fscanf */
        if(fscanf(stdin, "%63s", p) == EOF){
        fprintf(stdout, "\nErrore, impossibile leggere i dati\n");
        tcsetattr(STDIN_FILENO, TCSANOW, &term_orig);
        exit(EXIT_FAILURE);
    };
        /* Reimposto il terminale allo stato originale */
        tcsetattr(STDIN_FILENO, TCSANOW, &term_orig);
}

I would like to know if it is correct that the function get_pass haven’t a return code?

In this function I read the password with fscanf and then I think that I have to return it to the main program…but:

1. I don’t know how (with return p; I got a warning)
2. It works also without return p; so I think that it is all ok…but I’m not so sure…

I don’t understand how return work with functions.

Answer 1

int main() 
{
   char * password = NULL;

   get_pass(&password); //that is how you want to pass pointer to pointer

}

void get_pass(char **password) 
{

//1. get password using scanf from stdin or whatever way you want. 
//2. assign it to *password 
//3. no need to return anything

}

Remember, you need to handle memory allocation for password string. Let’s say you want to fix the password size to MAX_PASS_SIZE, then allocate that much memory either in main() or in get_pass so that you don’t corrupt your stack memory. The above snippet I wrote just shows how to populate value into password, which probably is your main question, i.e. pass a pointer to pointer.