您好我正在使用一些共享内存在不同的进程读取和写入数据。我正在使用消息队列来存储数据在读取和写入操作之间发生更改的消息。消息队列。 msgsend msgrcv。系统V在C系统调用(Linux)
/* struct that defines a message */
struct msgbuf{
long mtype; /* must be positive */
int childId; //ID of child sending message
int bufferChanged; //Buffer at which value was changed
int beforeValue; //Value before child sleeps
int afterValue; //Value after child sleeps
};
所以在阅读,写作和检查的变化过程店的消息通过以下方式
struct msgbuf msg = {BUFFER_CHANGED, id, position, read, bufferArr[position]};
if(msgsnd(msqid, &msg, sizeof(msg), 0)== -1){
perror("msgsnd in read.write");
}
这是工作的罚款。哦,顺便说一下,我如何创建消息队列。
#define BUFFER_CHANGED 1
qKey = ftok("./", 'A');
msqid = msgget(qKey, (IPC_CREAT | 0666));
/*Perform the following if the call is unsuccessful.*/
if(msqid == -1){
printf ("\nThe msgget call failed, error number = %d\n", errno);
}
/*Return the msqid upon successful completion.*/
else{
printf ("\nMessage queue successful. The msqid = %d\n", msqid);
//exit(0);
}
所以我的问题是,我不太清楚如何从队列中检索消息并将它们显示在屏幕上。我一直在阅读msgrcv()
系统调用,但对我来说不是很清楚。
rc = msgrcv(msqid, &msg, sizeof(msg), BUFFER_CHANGED, IPC_NOWAIT);
rc
为int
因为msgrcv()
返回一个int
。我如何将这个int
指向实际的消息?如何从消息中读取内容,以便我可以显示它们?我假设这应该在某种循环中完成。