ATMega 328p: function to get Unique Id

uid.ino

#include <avr/boot.h>

void setup(void)
{
  Serial.begin(9600);
  Serial.println(GetUID());
}

void loop()
{
}

String GetUID() {
  String uid = "";
  #define SIGRD 5
  #if defined(SIGRD) || defined(RSIG)
    for (uint8_t i = 14; i < 24; i += 1) {
      char buffer[1];
      sprintf(buffer, "%x", boot_signature_byte_get(i));
      uid += buffer;
    }
  #endif
  return uid;
}