serial communication in linux,using c

hi guys:
my serial code works well,AND NOTwant to use QextSerialPort:

Code:

---

int main(void)
{
	int fd,nread;
	struct  termios Opt;
	char buff[512];
	/*以读写方式打开串口*/
	fd = open( "/dev/ttySAC2", O_RDWR|O_NONBLOCK);
	if(-1 == fd)
	{ 
		perror("提示错误！");/* 不能打开串口一*/
		return 1;
	}
	//获取属性
	tcgetattr(fd, &Opt);
	tcflush(fd, TCIOFLUSH);
	//设置为19200Bps
	cfsetispeed(&Opt,B115200);
	cfsetospeed(&Opt,B115200);
	//8位数据位
	Opt.c_cflag &= ~CSIZE;
	Opt.c_cflag |= CS8;
	//无校验
	Opt.c_cflag &= ~PARENB;   /* Clear parity enable */
	Opt.c_iflag &= ~INPCK;
	//1停止位
	Opt.c_cflag &= ~CSTOPB;
	//
	Opt.c_cc[VTIME] = 150; /* 设置超时15 seconds*/   
	Opt.c_cc[VMIN] = 0; /* Update the options and do it NOW */
 
	//设置属性
	tcsetattr(fd,TCSANOW,&Opt);
	tcflush(fd, TCIOFLUSH);
 
	//
	while(!quit)
	{   
		while((nread = read(fd, buff, 512))>0)
		{ 
			buff[nread+1] = '\0';   
			write(fd,buff,nread);
		}
	}
	printf("quit\n");
	close(fd);  
	exit (0);
}

---

now i want to place it into a class ,inherited from QThread.
however，when i invoke close(fd), it report error.because close() is QT's default function to close the dialog.
how can i solve this problem?

i have fixed the error:
::close(fd);:p

another question:
this code seems not to run as expected.
i want read() a char and write() it back.
but now when i read() a char,the write() method has no effect.
that's to say:
it never go to:

Code:

---

buff[nread+1] = '\0';   
write(fd,buff,nread);

---

HOWEVER,my serial terminal can receive the char i press!!!
what's wrong with this code? :(

How is this question related to Qt exactly?

well , later i will put the read() in a QThread, and use postEvent() to communicate with main dialog. hope you could help :)