Bluetooth scan and reading serial (tested on Raspberry PI) from https://www.raspberrypi.org/forums/viewtopic.php?t=191456 and https://people.csail.mit.edu/albert/bluez-intro/x502.html

scan.cpp

#compile with : g++ -o scan scan.cpp -lbluetooth
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>
#include <cerrno>

int main(int argc, char **argv)
{
	char buf[1024] = {0};
	int bluetoothSocket, client, bytes_read;
	struct sockaddr_rc loc_addr = {0};
	struct sockaddr_rc client_addr = {0};

	socklen_t opt = sizeof(client_addr);

	bdaddr_t my_bdaddr_any = {0, 0, 0, 0, 0, 0};
	 
	bluetoothSocket = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
	 
	loc_addr.rc_family = AF_BLUETOOTH;
	loc_addr.rc_bdaddr = (bdaddr_t)my_bdaddr_any;
	loc_addr.rc_channel = (uint8_t) 1;

	int ret = -1;

	if ((ret = bind(bluetoothSocket, (struct sockaddr *)&loc_addr, sizeof(loc_addr))) == -1)	 
	{
	  printf("Bluetooth bind failed. ERRNO=%d\n", errno);
	  char *errorMessage = strerror_r(errno, buf, 1024);
	  printf("%s\n", errorMessage);
	  return 0;
	}
		
	ret = -1;

	if((ret = listen(bluetoothSocket, 1)) == -1)
	{
	  printf("Bluetooth listen failed. ERRNO=%d\n", errno);
	  char *errorMessage = strerror_r(errno, buf, 1024);
	  printf("%s\n", errorMessage);
	  return 0;
	}
       bool stopThread = false;

	while (stopThread == false)
	{
	  printf("Waiting for new client to connect.\n");
		
	  client = accept(bluetoothSocket, (struct sockaddr *)&client_addr, &opt);
		
	  if (client == -1)
	  {
	    printf("Bluetooth connect failed.\n");
	    close(client);
            usleep(1000000);
	    //delay(1000);
	    continue;
	  }
				
	  printf("Bluetooth connection made.\n");
		
	  ba2str(&loc_addr.rc_bdaddr, buf);
	  fprintf(stderr, "accepted connection from %s\n", buf);
	  memset(buf, 0, sizeof(buf));

	  // read data from the client
	  bytes_read = read(client, buf, sizeof(buf));
	  if (bytes_read > 0) 
	  {
	    printf("Bluetooth bytes received [%s]\n", buf);
            for (int i = 0; i < bytes_read;i++){
                    printf("%d\n", buf[i]);             }
	  }
	}			

	close(client);
	close(bluetoothSocket);
	return 0;
}