用一个消息队列（System V）实现客户端-服务器端

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1)类型字段可用于标识消息，从而允许多个进程在单个队列上复用消息。

2)类型字段可用作优先级字段。这允许接收者以不同于先进先出的某个顺序读出各个消息。使用管道或FIFO时，数据必须以写入的顺序读出。使用System V消息队列时，消息能够以任意顺序读出，只要跟消息类型关联的值一致就行。

#include<stdio.h>#include<sys/types.h>#include<sys/ipc.h>#include<sys/msg.h>#include<string.h>#define KEY_MSG 0x101#define MSGSIZE 64typedef struct{  long mtype;  char mtext[MSGSIZE];}msgbuf;#define LEN sizeof(msgbuf)-sizeof(long)void main(){  int msgid;  msgbuf buf1,buf2;  msgid=msgget(KEY_MSG,IPC_CREAT|0666);  while(1)    {      msgrcv(msgid,&buf1,LEN,1L,0);  //接收1的消息，返回类型为1L的第一个消息      printf("Receive client1 message:%s\n",buf1.mtext);      if(buf1.mtext[0]=='x' || buf1.mtext[0]=='X'){  strcpy(buf1.mtext,"x");  buf1.mtype=3L;  msgsnd(msgid,&buf1,LEN,0);  buf1.mtype=4L;  msgsnd(msgid,&buf1,LEN,0);  break;}      buf1.mtype=4L;               //设置消息类型为4L      msgsnd(msgid,&buf1,LEN,0);   //将从1接收到的消息发送给2      msgrcv(msgid,&buf2,LEN,2L,0);  //接收2的消息      printf("Receive client2 message:%s\n",buf2.mtext);      if(buf2.mtext[0]=='x' || buf2.mtext[0]=='X'){  strcpy(buf2.mtext,"x");  buf2.mtype=3L;  msgsnd(msgid,&buf2,LEN,0);  buf2.mtype=4L;  msgsnd(msgid,&buf2,LEN,0);  break;}      buf2.mtype=3L;               //设置消息类型为3L      msgsnd(msgid,&buf2,LEN,0);   //将从2接收到的消息发送给1    }  sleep(1);  msgctl(msgid,IPC_RMID,NULL);}

//client1.c#include<stdio.h>#include<sys/types.h>#include<sys/ipc.h>#include<sys/msg.h>#include<string.h>#define KEY_MSG 0x101#define MSGSIZE 64typedef struct{  long mtype;  char mtext[MSGSIZE];}msgbuf;#define LEN sizeof(msgbuf)-sizeof(long)void main(){  int msgid;  msgbuf buf1,buf2;  msgid=msgget(KEY_MSG,0666);  while(1)    {      printf("Input the mag to client2:");      gets(buf1.mtext);      buf1.mtype=1L;      msgsnd(msgid,&buf1,LEN,0);      msgrcv(msgid,&buf2,LEN,3L,0);      if(buf2.mtext[0]=='x'||buf2.mtext[0]=='X'){  printf("client1 will quit\n");  break;}      else printf("Recevie from client2,message:%s\n",buf2.mtext);    }}

//client2.c#include<stdio.h>#include<sys/types.h>#include<sys/ipc.h>#include<sys/msg.h>#include<string.h>#define KEY_MSG 0x101#define MSGSIZE 64typedef struct{  long mtype;  char mtext[MSGSIZE];}msgbuf;#define LEN sizeof(msgbuf)-sizeof(long)void main(){  int msgid;  msgbuf buf1,buf2;  msgid=msgget(KEY_MSG,0666);  while(1)    {      msgrcv(msgid,&buf2,LEN,4L,0);      if(buf2.mtext[0]=='x'||buf2.mtext[0]=='X'){  printf("client2 will quit!\n");  break;}      else printf("Receive from client1,message:%s\n",buf2.mtext);      sleep(1);      printf("Input the msg to clinet1:");      gets(buf1.mtext);      buf1.mtype=2L;      msgsnd(msgid,&buf1,LEN,0);    }}

其中的消息类型：

1L： client1------------------>server

2L： client2------------------>server

3L： server------------------>client1

4L： server------------------>client2

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