求助！会者不难，难者不会

代码:

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <errno.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
#include <stdlib.h>
//设置串口
int set_opt(int fd,int nSpeed, int nBits, char nEvent, int nStop)
{
struct termios newtio,oldtio;

if ( tcgetattr( fd,&oldtio) != 0) {
perror("SetupSerial 1");
return -1;
}
bzero( &newtio, sizeof( newtio ) );

newtio.c_cflag |= CLOCAL | CREAD;
newtio.c_cflag &= ~CSIZE;

switch( nBits )
{
case 7:
newtio.c_cflag |= CS7;
break;
case 8:
newtio.c_cflag |= CS8;
break;
}

switch( nEvent )
{
case 'O':
newtio.c_cflag |= PARENB;
newtio.c_cflag |= PARODD;
newtio.c_iflag |= (INPCK | ISTRIP);
break;
case 'E':
newtio.c_iflag |= (INPCK | ISTRIP);
newtio.c_cflag |= PARENB;
newtio.c_cflag &= ~PARODD;
break;
case 'N':
newtio.c_cflag &= ~PARENB;
break;
}

switch( nSpeed )
{
case 2400:
cfsetispeed(&newtio, B2400);
cfsetospeed(&newtio, B2400);
break;
case 4800:
cfsetispeed(&newtio, B4800);
cfsetospeed(&newtio, B4800);
break;
case 9600:
cfsetispeed(&newtio, B9600);
cfsetospeed(&newtio, B9600);
break;
case 115200:
cfsetispeed(&newtio, B115200);
cfsetospeed(&newtio, B115200);
break;
case 460800:
cfsetispeed(&newtio, B460800);
cfsetospeed(&newtio, B460800);
break;
default:
cfsetispeed(&newtio, B9600);
cfsetospeed(&newtio, B9600);
break;
}

if( nStop == 1 )
newtio.c_cflag &= ~CSTOPB;
else if ( nStop == 2 )
newtio.c_cflag |= CSTOPB;

newtio.c_cc[VTIME] = 0;
newtio.c_cc[VMIN] = 0;

tcflush(fd,TCIFLUSH);

if((tcsetattr(fd,TCSANOW,&newtio))!=0)
{
perror("com set error");
return -1;
}
printf("set done!\n");
return 0;
}





/*打开串口函数*/
int open_port(int fd,int comport)
{
char *dev[]={"/dev/ttyS0","/dev/ttyS1","/dev/ttyS2"};
long vdisable;
if (comport==1)//串口1
{ fd = open( "/dev/ttyS0", O_RDWR|O_NOCTTY|O_NDELAY);
if (-1 == fd){
perror("Can't Open Serial Port");
return(-1);
}
}
else if(comport==2)//串口2
{ fd = open( "/dev/ttyS1", O_RDWR|O_NOCTTY|O_NDELAY);
if (-1 == fd){
perror("Can't Open Serial Port");
return(-1);
}
}
else if (comport==3)//串口3
{
fd = open( "/dev/ttyS2", O_RDWR|O_NOCTTY|O_NDELAY);
if (-1 == fd){
perror("Can't Open Serial Port");
return(-1);
}
}
/*恢复串口为阻塞状态*/
if(fcntl(fd, F_SETFL, 0)<0)
printf("fcntl failed!\n");
else
printf("fcntl=%d\n",fcntl(fd, F_SETFL,0));
/*测试是否为终端设备*/
if(isatty(STDIN_FILENO)==0)
printf("standard input is not a terminal device\n");
else
printf("isatty success!\n");
printf("fd-open=%d\n",fd);
return fd;
}

//主函数
int main(void)
{

int fd;
int nread,nwrite,i;
char buff[12];
fd_set rd;

if((fd=open_port(fd,1))<0){
perror("open_port error");
return;
}

if((i=set_opt(fd,115200,8,'N',1))<0){
perror("set_opt error");
return;
}

FD_ZERO(&rd);
FD_SET(fd,&rd);

while(1){

if(select(fd+1,&rd,NULL,NULL,NULL)<0)
perror("select");
else{
while(  (nread = read(fd,buff,12)) >0)
{buff[12]='\0';
printf("%s",buff);

}

}
}

return 0;

}