Question

I am having some problems when returning with printf of a char array from a struct in C.

struct q_entry
{
    long mtype;
    char mtext[MAXLENGTH + 1];
};

The long mtype from the struct is returning fine, but the string is just returning some weird characters.

int proc_obj(struct q_entry *msg)
{
    printf("\npriority: %ld name: %s\n", msg->mtype, msg->mtext);
}

It just returns some strange characters like “priority: 1 name: ▒▒(” and not “priority: 1 name: hello”

I am populating the struct using the following code

int enter(char *objname, int priority)
{
    ...

    strncpy(s_entry.mtext, objname, sizeof(s_entry.mtext) - 1);
    s_entry.mtype = priority;

    // Send the message
    if (msgsnd(s_qid, &s_entry, len, 0) == -1)
    {
        printf("error: msgsnd failed\n");
        return(-1);
    }
    else
    {
        return(0);
    }
}

I don’t have much experience with C, so I don’t know too much about using structs. Please let me know if more context or parts of the code is needed. Any kind of help would be very helpful.

I have added a little more code in enter above, and here is more code of the when enter and proc_obj are called

main(int argc, char **argv)
{
    int priority;

    if (argc != 3)
    {
        printf("error: incorrect number of arguments\n");
        exit(1);
    }
    else
    {
        priority = atoi(argv[2]);
    }

    if (enter(argv[1], priority) < 0)
    {
        printf("error: message entering failed\n");
        exit(1);
    }

    exit(0);
}

This is in a different file from enter and above code

int server(void)
{
    int mlen, r_qid;
    struct q_entry r_entry;

    // Initialize queue
    if ((r_qid = init_queue()) == -1)
        return(-1);

    for (;;)
    {
        if ((mlen = msgrcv(r_qid, &r_entry, MAXLENGTH, (-1 * MAXPRIOR), MSG_NOERROR)) == -1)
        {
            printf("error: msgrcv failed\n");
            exit(1);
        }
        else
        {
            proc_obj(&r_entry);
        }
    }
}

Answer 1

Answer before adding more code

It looks like the s_entry structure object is local, and enter works on the local variable. How are you calling enter and returning the structure after you have done initializing it ? note that you have int as the return type of the enter function. If you are doing return s_entry; then the output you are getting is possible, as only the first word of the structure, ie the lower sizeof (int) part of mtype is considered.

If you are using enter function like this as i described above then make the return type of enter to struct s_entry

---

You should check the size of len when sending the message.