Linux 进程间通讯详解三

msgctl()函数
int msgctl(int msqid, int cmd, struct msqid_ds *buf);
--参数
    msqid：有msgget函数返回的消息队列标识码
    cmd：是将要采取的动作
--成功返回0，失败返回-1
--cmd的三个取值
    IPC_STAT--把msqid_ds结构中的数据设置为消息队列的当前关联值
    IPC_SET--在进程有足够权限的前提下，把消息队列的当前关联值设置为msqid_ds数据结构中给出的值
    IPC_RMID--删除消息队列

struct msqid_ds {
               struct ipc_perm msg_perm;     /* Ownership and permissions */
               time_t          msg_stime;    /* Time of last msgsnd(2) */
               time_t          msg_rtime;    /* Time of last msgrcv(2) */
               time_t          msg_ctime;    /* Time of last change */
               unsigned long   __msg_cbytes; /* Current number of bytes in
                                                queue (non-standard) */
               msgqnum_t       msg_qnum;     /* Current number of messages
                                                in queue */
               msglen_t        msg_qbytes;   /* Maximum number of bytes
                                                allowed in queue */
               pid_t           msg_lspid;    /* PID of last msgsnd(2) */
               pid_t           msg_lrpid;    /* PID of last msgrcv(2) */
           };

struct ipc_perm {
               key_t          __key;       /* Key supplied to msgget(2) */
               uid_t          uid;         /* Effective UID of owner */
               gid_t          gid;         /* Effective GID of owner */
               uid_t          cuid;        /* Effective UID of creator */
               gid_t          cgid;        /* Effective GID of creator */
               unsigned short mode;        /* Permissions */
               unsigned short __seq;       /* Sequence number */
           };

//消息队列--msgctl()函数
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

int main(int arg, char * args[])
{
    int ret = 0;
    int msgid = msgget(0x1234, 0666);
    if (msgid == -1)
    {
        perror("msgget() err");
        return -1;
    }
    printf("访问消息队列成功！msqid=%d
", msgid);
    struct msqid_ds buf;
    memset(&buf, 0, sizeof(buf));
    ret = msgctl(msgid, IPC_STAT, &buf);
    if (ret == -1)
    {
        perror("msgctl() err");
        return -1;
    }
    printf("权限位：%o
", buf.msg_perm.mode);
    //想要修改ipcs，需要先获取，然后再修改(这是正确的做法)
    buf.msg_perm.mode = 0666;
    ret = msgctl(msgid, IPC_SET, &buf);
    if (ret == -1)
    {
        perror("msgctl() err");
        return -1;
    }
    printf("修改ipcs成功!
");
    sleep(20);
    ret = msgctl(msgid, IPC_RMID,NULL);
    if (ret == -1)
    {
        perror("msgctl() err");
        return -1;
    }
    printf("删除ipcs成功!
");
    return 0;
}