Question

Here’s my code:

tmpip = get_public_ip();
pubip = strtok(tmpip, "\n");
sprintf(buffer, "220 FTPUtils Server [%s]", pubip);
len_string = strlen(buffer)+1;
if(send(newsockd, &len_string, sizeof(len_string), 0) < 0){
    perror("Errore invio len buffer");
    onexit(newsockd, sockd, 0, 2);
}
if(send(newsockd, buffer, len_string, 0) < 0){
    perror("Errore durante l'invio");
    onexit(newsockd, sockd, 0, 2);
}
pubip = NULL;
free(tmpip);
memset(buffer, 0, sizeof(buffer));


if(recv(newsockd, &len_string, sizeof(len_string), MSG_WAITALL) < 0){
    perror("Errore ricezione len user buffer");
    onexit(newsockd, sockd, 0, 2);
}
if(recv(newsockd, buffer, len_string, 0) < 0){
    perror("Errore ricezione del nome utente");
    onexit(newsockd, sockd, 0, 2);
}       
user_string = strtok(buffer, " ");
username = strtok(NULL, "\n");
fprintf(stdout, "%s %s\n", user_string, username);
sprintf(saved_user, "%s", username);
memset(buffer, 0, sizeof(buffer));

if(recv(newsockd, &len_string, sizeof(len_string), MSG_WAITALL) < 0){
    perror("Errore ricezione len pass buffer");
    onexit(newsockd, sockd, 0, 2);
}
if(recv(newsockd, buffer, len_string, 0) < 0){
    perror("Errore ricezione password");
    onexit(newsockd, sockd, 0, 2);
}
pass_string = strtok(buffer, " ");
password = strtok(NULL, "\n");
fprintf(stdout, "%s %s\n", pass_string, password);
memset(buffer, 0, sizeof(buffer));

printf("%s %s\n", username, password);

I have a problem with the last debug printf: it prints to stdout nothing!!
Why are my pointer (username and password) cleared???
It is strange because the 2 fprintf works perfectly but the last printf no…

Answer 1

Both the username and the password point to locations inside buffer. That’s how strtok works.

In other words, when you zero the buffer using memset you’re zeroing out the memory to which username and password point. A simple workaround would be to duplicate that memory:

username = strtok(NULL, "\n");
username = strdup(username);

Note strdup isn’t standard but quite easy to implement using malloc and strcpy.