創建兩個進程，使每個都能讀寫消息隊列
代碼：
msg_service.c

#include <sys/ipc.h> #include <sys/msg.h> #include <stdlib.h> #include <string.h> #include <unistd.h>struct msgbuf {long mtype;char mtest[128];char ID[4]; };int main() {struct msgbuf sendbuf,readbuf;int msgid;key_t key;pid_t pid;int readret;key=ftok("b.c",5);msgid = msgget(key,0755|IPC_CREAT);if(msgid == -1){printf("create message queue failed!\n");return -1;}system("ipcs -q");printf("create message queue success msgid =%d\n",msgid);sendbuf.mtype=100;pid=fork();if(pid ==-1){printf("fork fail\n");return -1;}if(pid > 0)//父進程發送消息類型為100的消息給消息隊列{while(1){memset(sendbuf.mtest,0,128);printf("please input to massage queue:\n");fgets(sendbuf.mtest,128,stdin);msgsnd(msgid,(void *)&sendbuf,strlen(sendbuf.mtest),0);}}if(pid == 0)//子進程從消息隊列中讀取消息類型為100的消息{while(1){memset(readbuf.mtest,0,128);readret=msgrcv(msgid,(void *)&readbuf,128,99,0);printf("receive byte form message queue is :%s\n",readbuf.mtest);printf("total have %d byte\n",readret);}}return 0;}

代碼：
msg_client.c

#include <stdio.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> #include <stdlib.h> #include <string.h> #include <unistd.h>struct msgbuf {long mtype;char mtest[128];char ID[4]; };int main() {struct msgbuf sendbuf,readbuf;int msgid;key_t key;pid_t pid;int readret;key=ftok("b.c",5);msgid = msgget(key,0755|IPC_CREAT);if(msgid == -1){printf("create message queue failed!\n");return -1;}system("ipcs -q");printf("create message queue success msgid =%d\n",msgid);sendbuf.mtype=99;pid=fork();if(pid ==-1){printf("fork fail\n");return -1;}if(pid == 0)//子進程發送消息類型為99的消息給消息隊列{while(1){//memset(sendbuf.mtest,0,128);printf("please input to massage queue:\n");fgets(sendbuf.mtest,128,stdin);msgsnd(msgid,(void *)&sendbuf,strlen(sendbuf.mtest),0);memset(sendbuf.mtest,0,128);}}if(pid > 0)//父進程讀取消息類型為100的消息{while(1){memset(readbuf.mtest,0,128);readret=msgrcv(msgid,(void *)&readbuf,128,100,0);printf("receive byte form message queue is :%s\n",readbuf.mtest);printf("total have %d byte\n",readret);}}return 0;}```執行結果：  這時兩個進程可進行通信。程序執行流程： msgsnd(msgid,(void *)&sendbuf,strlen(sendbuf.mtest),0);中最后的參數0表示，當消息返送完才返回，所以沒有消息發送時，進程會一直卡在這，msgrcv(msgid,(void *)&readbuf,128,100,0);中最后一個參數0表示，若無消息函數一直阻塞，所以沒有讀取到消息時，函數也會一直卡在這。

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