嵌入式技术
#include
//获取key值, key值是System V IPC的标识符,成功返回key,失败返回-1设errno//同pathname+同 proj_id==>同key_t;key_t ftok(const char *pathname, int proj_id);
pathname :文件名
proj_id: 1~255的一个数,表示project_id
key_t key=ftok(".",100); //“.”就是一个存在且可访问的路径, 100是假设的proj_id if(-1==key) perror("ftok"),exit(-1);
//创建/获取消息队列,成功返回shmid,失败返回-1int msgget(key_t key, int msgflg); //ATTENTION:用int msqid=msgget()比较好看
msgflg:具体的操作标志
消息队列的容量由msg_qbytes控制,在消息队列被创建的过程中,这个大小被初始化为MSGMNB,这个限制可以通过msgctl()修改
int msqid=msgget(key,IPC_CREAT|IPC_EXCL|0664);if(-1==msqid) perror("msgget"),exit(-1);
//向指定的消息队列发送指定的消息,如果消息队列已经满了,默认的行为是堵塞,直到队列有空间容纳新的消息,成功返回0,失败返回-1设errnoint msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);
msqid msgget()返回的消息队列的ID
msgp消息的的首地址, 消息的参考数据类型如下
struct msgbuf { long mtype; /* message type, must be > 0 */ //消息的类型 char mtext[1]; /* message data */ //消息的内容};ATTENTION:The mtext field is an array (or other structure) whose size is specified by msgsz, a nonnegative integer value.
msgsz消息的大小, 该参数用于指定消息内容的大小, 不包括消息的类型。只能sizeof(Msgbuf.mtext),不能sizeof(Msgbuf)
msgflg发送的标志, 默认给0即可
Msg msg1={1,"hello"};//消息的类型是1,内容是helloint res=msgsnd(msqid,&msg2,sizeof(msg2.buf),0);if(-1==res) perror("msgsnd"),exit(-1);
//向指定的消息队列取出指定的消息,成功返回实际接受到的byte数,失败返回-1设errnossize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp, int msgflg);
msqid: 消息队列的ID(returned by msgget)
msgp: 存放接收到消息的缓冲区首地址
msgsz: 消息的最大大小, 不包括消息的类型==>只能sizeof(Msgbuf.mtext),不能sizeof(Msgbuf)
msgtyp: 消息的类型
msgflg: 发送的标志, 默认给0即可
Msg msg1;int res=msgrcv(msqid,&msg1,sizeof(msg1.buf),1,0);if(-1==res) perror("msgrcv"),exit(-1);
// 消息操作,成功返回0,失败返回-1设errnoint msgctl(int msqid, int cmd, struct msqid_ds *buf);
msqid :消息队列的ID,由msgget()
buf 结构体指针
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 (nonstandard) */ 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 */};
cmd
IPC_INFO (Linux-specific)返回整个系统对与消息队列的限制信息到buf指向的结构体中
//_GNU_SOURCE//
int res=msgctl(msqid,IPC_RMID,NULL);if(-1==res)perror("msgctl"),exit(-1);
//Sys V IPC msg#include
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