COM-Port unter Linux ansteuern

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
 
int com_port;  
//char get_buffer[9];
const char* get_buffer;
 
int init_com() {  
  struct termios options;
  //COM1
  com_port = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
  if (com_port == -1) {
    printf("send_to_com: Unable to open /dev/ttyS0!\n");
    return -1;
  } else {
    fcntl(com_port, F_SETFL, 0);
  }
 
  //get the current options for the port
  tcgetattr(com_port, &options);
 
  //set the baud rates to 4800
  cfsetispeed(&options, B4800);
 
  cfsetospeed(&options, B4800);
 
  //enable the receiver and set local mode
  options.c_cflag |= (CLOCAL | CREAD);
 
  //set the new options for the port
  tcsetattr(com_port, TCSANOW, &options);
 
  #ifdef DEBUG
  printf("/dev/ttyS0 was opened successfully!\n");
  #endif
  return 0;
}
 
void send_to_com(char buffer[9]) {  
  write(com_port, buffer, 9);
  #ifdef DEBUG
  printf("wrote %s to /dev/ttyS0\n", buffer);
  #endif
}  
 
void get_from_com() {  
  read(com_port, get_buffer, sizeof(get_buffer));
  #ifdef DEBUG
  printf("read %s to /dev/ttyS0\n", get_buffer);
  #endif
}  
 
int main (void) {  
  init_com();
  send_to_com("00??00??\r");
  get_from_com();
  printf("%s", get_buffer);
  return 0;
}