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头文件

#define MSGKEY 1183

struct msgform {
	long mtype;
	int source_pid;	
	double a,b;
	char opcode;
	double result;
	char result_msg[128];
}msg;
int msgsize=sizeof(struct msgform)-sizeof(long);
int msgqid;

server.c


#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

#include <msg_mycs.h>

main()
{
	int i;
	
	extern cleanup();
	for(i=0;i<20;i++)
	 signal(i,cleanup);

	msgqid = msgget(MSGKEY,0777|IPC_CREAT);

	for(;msg.opcode!='q';)
	{
 	 printf("server pid= %d is ready (msgqid=%d)... \n",getpid(),msgqid);

	 msgrcv(msgqid,&msg,msgsize,1,0);
	 printf("server: receive from pid=%d\n",msg.source_pid);
         msg.result_msg[0]='1';
         switch(msg.opcode){
	 case '+':
		msg.result=msg.a+msg.b;
		break;

	 case '-':
		msg.result=msg.a-msg.b;
		break;

	 case '*':
		msg.result=msg.a*msg.b;
		break;
	 case '/':
		if(msg.b!=0)
	 	 msg.result=msg.a/msg.b;
                else
                 strcpy(msg.result_msg,"0. divide by 0.");
		break;
	 default:
                 strcpy(msg.result_msg,"0. exit by user.") ;
		break;
	 }

         if(msg.result_msg[0]=='1')
		printf("%.2f  %c %.2f = %.2f\n",msg.a,msg.opcode,msg.b,msg.result);
         else
	    printf("%s\n",msg.result_msg);

	 msg.mtype=msg.source_pid;
	 msg.source_pid=getpid();
	 msgsnd(msgqid,&msg,msgsize,0);
	}
        printf("server exit by client pid=%d\n",msg.mtype);
}
cleanup()
{
	msgctl(msgqid,IPC_RMID,0);
	exit(0);
}

client.c

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <msg_mycs.h>
main()
{
	struct msgform msg;
	int pid;
	
	msgqid = msgget(MSGKEY,0777);
        
        pid=getpid();
	for(;msg.opcode!='q';){
         printf("a=");
	 scanf("%lf",&msg.a);
   
         printf("b=");
	 scanf("%lf",&msg.b);
   
         printf("opcode=(+,-,*,/,q for EXIT)");

	msg.opcode=getchar();
	while(msg.opcode=='\n')msg.opcode=getchar();
         
        if(msg.opcode=='+'||msg.opcode=='-'||'*'==msg.opcode ||
                '/'==msg.opcode||'q'==msg.opcode)
         { 
          msg.source_pid=pid;
          msg.mtype=1;
	 
	  msg.result_msg[0]=0;
	  msgsnd(msgqid,&msg,msgsize,0);
	  msgrcv(msgqid,&msg,msgsize,pid,0);
	  
	  printf("client: receive from pid=%d\n",msg.source_pid);
         
          if(msg.result_msg[0]=='1')
		printf("%.2f  %c %.2f = %.2f\n",msg.a,msg.opcode,msg.b,msg.result);
	  else
	    printf("%s\n",msg.result_msg);
         

         }
        }
}