Why is msgrcv() feeding garbage characters into the buffer? - c++

Question

right now, I am currently trying to output the contents of buf.mtext so I can make sure take the correct input before moving on with my program. Everything seems to work fine, except one thing; msgrcv() puts garbage characters into the buffer, and the reciever process outputs garbage characters.
Here is my sender process:
int main (void)
{
int i; // loop counter
int status_01; // result status
int msqid_01; // message queue ID (#1)
key_t msgkey_01; // message-queue key (#1)
unsigned int rand_num;
float temp_rand;
unsigned char eight_bit_num;
unsigned char counter = 0;
unsigned char even_counter = 0;
unsigned char odd_counter = 0;
srand(time(0));
struct message {
long mtype;
char mtext[BUFFER_SIZE];
} buf_01;
msgkey_01 = MSG_key_01; // defined at top of file
msqid_01 = msgget(msgkey_01, 0666 | IPC_CREAT)
if ((msqid_01 <= -1) { exit(1); }
/* wait for a key stroke at the keyboard ---- */
eight_bit_num = getchar();
buf_01.mtype = 1;
/* send one eight-bit number, one at a time ------------ */
for (i = 0; i < NUM_REPEATS; i++)
{
temp_rand = ((float)rand()/(float)RAND_MAX)*255.0;
rand_num = (int)temp_rand;
eight_bit_num = (unsigned char)rand_num;
if ((eight_bit_num % 2) == 0)
{
printf("Even number: %d\n", eight_bit_num);
even_counter = even_counter + eight_bit_num;
}
else
{
printf("Odd number: %d\n", eight_bit_num);
odd_counter = odd_counter + eight_bit_num;
}
/* update the counters ------------------------------ */
counter = counter + eight_bit_num;
if((eight_bit_num % 2) == 0) { even_counter = even_counter + eight_bit_num; }
else { odd_counter = odd_counter + eight_bit_num; }
buf_01.mtext[0] = eight_bit_num; // copy the 8-bit number
buf_01.mtext[1] = '\0'; // null-terminate it
status_01 = msgsnd(msqid_01, (struct msgbuf *)&buf_01, sizeof(buf_01.mtext), 0);
status_01 = msgctl(msqid_01, IPC_RMID, NULL);
}
Here is my receiver process:
int main() {
struct message {
long mtype;
char mtext[BUFFER_SIZE];
} buf;
int msqid;
key_t msgkey;
msgkey = MSG_key_01;
msqid = msgget(msgkey, 0666); // connect to message queue
if (msqid < 0) {
printf("Failed\n");
exit(1);
}
else {
printf("Connected\n");
}
if (msgrcv(msqid, &buf, BUFFER_SIZE, 0, 0) < 0) { // read message into buf
perror("msgrcv");
exit(1);
}
printf("Data received is: %s \n", buf.mtext);
printf("Done receiving messages.\n");
return 0;
}
The output is usually something like as follows:
Data received is: ▒
Done receiving messages.
I have made sure to clear my message queues each time after running the sender and receiver processes, as well, since I have come to find out this can cause issues. Thanks in advance for your help.

Answer 1

Turns out neither of the suggested solutions were the issue, as I suspected; the sender process actually works just fine. The problem was that I was trying to print buf.mtext instead of buf.mtext[0] which isn't an actual integer value. I fixed the issue by just doing this:
int temp_num = buf.mtext[0];
printf("Data recieved is %d \n", temp_num);