Linux编程：进程间通信--消息队列

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1.父进程创建消息队列和两个子进程p1和p2
2.子进程p1打开给定文件（如果没有，则创建文件），并向文件中写数据，写完关闭文件，然后向消息队列写入一条消息“ok”,目的是通知进程p2可以读取文件内容了。
3.子进程p2从消息队列读取消息，如果收到消息“ok”,则打开文件，读取文件内容，并将其输出道屏幕上，关闭文件。
代码部分：

/* * quque.c * *  Created on: Nov 10, 2016 *      Author: koala *//* * quque.c * *  Created on: Nov 10, 2016 *      Author: koala */#include <stdio.h>#include <unistd.h>#include <string.h>#include <sys/msg.h>typedef struct mymsg{    long mytype;    char mytext[128];}mymsg;int main(){    pid_t fpid,pid1,pid2; //Declare father process and two children processes    fpid = getpid();    struct mymsg msg;    char buff[100];    //Get key identification    //Create a  msg queue    int queueid = msgget(ftok(".",'t'),0660 | IPC_CREAT);    printf("The father process's PID is: %d\n",fpid);    char dir[100];//Declare file direction    if((pid1 = fork()) == 0)    {        printf("Children process1's PID is: %d and its father process's PID is: %d\n",getpid(),getppid());        FILE *fp;        printf("Please enter the file direction:\n");        fgets(dir,sizeof(dir)-1,stdin);        fp = fopen(dir,"w+");//Open file"hello pipe.txt",if failed then create        if(fp == NULL)        {            printf("The file cannot be open or create!\n");        }        else        {            //Write data to file            fwrite ("hello queue!", 1,sizeof("hello queue!")-1,fp );            fclose(fp);            fflush(fp);            strcat(msg.mytext ,"OK");            msgsnd(queueid,msg.mytext,sizeof(msg.mytext),IPC_NOWAIT);        }    }    wait(0);    if((pid2 = fork()) == 0)    {        printf("Children process2's PID is: %d and its father process's PID is: %d\n",getpid(),getppid());        msgrcv(queueid,msg.mytext,sizeof(msg.mytext),0,IPC_NOWAIT);        if(strcmp(msg.mytext,"OK"))        {            FILE *fpr;            fpr = fopen(dir,"r");            if(fpr == NULL)            {                printf("The file does not exist!\n");            }            else            {                while(fgets(buff,1024 ,fpr)!= NULL)                {                    fprintf(stderr,"%s",buff);                }                getchar();                fclose(fpr);            }        }    }    pid_t childpid = wait(NULL);    printf("Process of %d exited\n",childpid);    return 0;}

运行截图：
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