c++ - 为什么 msgrcv() 将垃圾字符输入缓冲区？

Question

现在，我正在尝试输出 buf.mtext 的内容，以便在继续我的程序之前确保采用正确的输入。一切似乎都运行良好，除了一件事； msgrcv()将垃圾字符放入缓冲区，接收进程输出垃圾字符。

这是我的发件人流程:

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);
}

这是我的接收进程:

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;
}

输出通常如下所示:

Data received is: ▒
Done receiving messages.

我也确保每次运行发送方和接收方进程后都清除消息队列，因为我发现这可能会导致问题。预先感谢您的帮助。

Answer 1

事实证明，正如我怀疑的那样，建议的解决方案都不是问题所在；发送进程实际上工作得很好。问题是我试图打印 buf.mtext 而不是 buf.mtext[0] ，它不是一个实际的整数值。我通过这样做解决了这个问题:

int temp_num = buf.mtext[0];
printf("Data recieved is %d \n", temp_num);