read the port

Read data from a serial port in C++:

1> open the port:

      fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
      if (fd == -1)
      {
       /*
 * Could not open the port.
 */

2> read the port: 
while ((nbytes = read(fd, bufptr, buffer + sizeof(buffer) - bufptr - 1)) > 0)
 {
   bufptr += nbytes;
   if (bufptr[-1] == '\n' || bufptr[-1] == '\r')
            break;
 }

3> writing the port: 
if (write(fd, "AT\r", 3) < 3)
   continue;