如果为空，请检查Unix Message Queue

Question

Can some one tell me how to check if there is any message in message queue. the message queue is implemented in C in linux based operating system. I just want to check if there is any message in the message queue at a particular time.

Answer 1

Just checking the amount (if any) of messages is done using the

msgctl() 

function, and examining the msqid_ds structure on return, the msg_qnum in this structure is the amount of messages in the queue. Here is a link with an example: msgctl example , it does more then you want, but after the msgctl() call you just have to check that field in the structure I mentioned above.

#include <sys/msg.h>

main() {
  int msqid = 2;
  int rc;
  struct msqid_ds buf;
  int num_messages;

  rc = msgctl(msqid, IPC_STAT, &buf);
  num_messages = buf.msg_qnum;
}

This example should do what you want, and only do what you want.