/************* *apptest.c* *************/#include <unistd.h>#include <sys/types.h>main(){	int pipe_fd[2];	pid_t pid;	char r_buf[4];	char** w_buf[256];	int childexit=0;	int i;	int cmd;		memset(r_buf,0,sizeof(r_buf));	if(pipe(pipe_fd)<0)	{		printf("pipe create error\n");		return -1;	}	if((pid=fork())==0)	//子進程：解析從管道中獲取的命令，并作相應的處理	{		printf("\n");		close(pipe_fd[1]);		sleep(2);				while(!childexit)		{				read(pipe_fd[0],r_buf,4);			cmd=atoi(r_buf);			if(cmd==0)			{printf("child: receive command from parent over\n now child process exit\n");				childexit=1;			}					       else if(handle_cmd(cmd)!=0)				return;			sleep(1);		}		close(pipe_fd[0]);		exit();	}	else if(pid>0)	//parent: send commands to child	{	close(pipe_fd[0]);	w_buf[0]="003";	w_buf[1]="005";	w_buf[2]="777";	w_buf[3]="000";	for(i=0;i<4;i++)		write(pipe_fd[1],w_buf[i],4);	close(pipe_fd[1]);	}	}//下面是子進程的命令處理函數（特定于應用）：int handle_cmd(int cmd){if((cmd<0)||(cmd>256))//suppose child only support 256 commands	{	printf("child: invalid command \n");	return -1;	}printf("child: the cmd from parent is %d\n", cmd);return 0;}