Segmentation fault in returning array from a class

edit

I'm facing a strange problem. I'm running the ROS node on Intel Edison and in the node I'm reading the Bluetooth LE device MAC address and its RSSI value from a class which I've written in an external file. All functions are working correctly except one. When I try to get back the data from scan.read_decvice function it runs correctly for the first time but in the next iteration I get a segmentation fault.

while (ros::ok())
{
    bl_talker::beacon le_msg;
    dev_info devices[20];
    int num_dev = scan.read_device(device, 20, devices);
    while(num_dev > 0)
    {
        if(devices[num_dev-1].valid == 1)
        {
            le_msg.mac = devices[num_dev-1].dev_mac;
            le_msg.rssi = devices[num_dev-1].dev_rssi;
            le_msg.msg_count = devices[num_dev-1].dev_count;

            printf("%d: %s - RSSI %d\n", le_msg.msg_count, le_msg.mac.c_str(), le_msg.rssi);
            chatter_pub.publish(le_msg);
            num_dev--;
        }
    }
    ros::spinOnce();
    loop_rate.sleep();
}

If I write the function in the same file where my main is written, it runs without any problem. Also it runs smoothly if I remove the ROS part. It would be great if anyone can help me out.