send.c:
    #include <stdio.h>
    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/msg.h>
    #include <string.h>
    typedef struct msgbuf{ //函式要求使用者自定義一個結構體
        long mtype;
        char mtext[128];//預設128個空間
    }msg_t;

    int main(void) {
        key_t key; //為了接收鍵值以確定ID
 

        msg_t mbuf;
        key = ftok(".",21);  //獲得一個鍵值
        if(key == -1) {
        perror("ftok");
        return -1;
        }
        printf("key=%x\n",key);
        //從核心獲取訊息佇列
        int msqid = msgget(key, IPC_CREAT|0664);
        if(msqid == -1) {
        perror("MSGGET");
        return -1
 
;
        }
        printf("msqid=0x%x\n",msqid);
       //初始化訊息
        mbuf.mtype = 3;
        strcpy(mbuf.mtext,"this is a test\n");
        //向訊息佇列傳送訊息
        int s = msgsnd(msqid, &mbuf, strlen(mbuf.mtext)+1, 0);
        if(s == -1) {
        perror("msgsnd");
        return -1;
        }

        return
 
 0;
        }
命令： [email protected]:~/day/day33$ a.out 
結果： key=15081b76
    msqid=0x0
命令： [email protected]:~/day$ ipcs  //察看當前列對中所佔的大小和訊息數

    ------ Shared Memory Segments --------
    key        shmid      owner      perms      bytes      nattch     status      
    0x00000000 0          tarena     600        393216     2          dest         
    0x00000000 32769      tarena     600        393216     2          dest         

    ------ Semaphore Arrays --------
    key        semid      owner      perms      nsems     

    ------ Message Queues --------
    key        msqid      owner      perms      used-bytes   messages    
    0x15081b76 0          tarena     664        15           1            //執行一次，寫入一次訊息，再執行一次會繼續追加

recv.c:
    #include <stdio.h>
    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/msg.h>
    #include <string.h>
    typedef struct msgbuf{
        long mtype;
        char mtext[128];
    }msg_t;

    int main(void) {
        key_t key;
        msg_t mbuf;
        key = ftok(".",21);
        if(key == -1) {
        perror("ftok");
        return -1;
        }
        printf("key=%x\n",key);
        //從核心獲取訊息佇列
        int msqid = msgget(key, IPC_CREAT|0664);
        if(msqid == -1) {
        perror("MSGGET");
        return -1;
        }
        printf("msqid=0x%x\n",msqid);
        //從訊息佇列獲取訊息
        int s = msgrcv(msqid, &mbuf, 128, 3, IPC_NOWAIT);//0是沒有訊息阻塞,IPC_NOWAIT是沒有訊息不阻塞
        if(s == -1) {
        perror("msgrcv");
        return -1;
        }
        printf("%s\n", mbuf.mtext);
        return 0;
    }

    [email protected]:~/day/day33$ rec
    key=15081b76
    msqid=0x0
    this is a test  //第一次訊息列對裡有訊息

    [email protected]:~/day/day33$ rec
    key=15081b76
    msqid=0x0
    msgrcv: No message of desired type  //第二次訊息列對裡沒有訊息，提示沒有訊息。