vector <index> reading_positions;

struct index {
    vector <string> file_names;
    vector <int> start_reading_positions;
    vector <int> end_reading_positions;
};

void save_read_position(int id, int start_position, int end_position) {
    index current_id;
    current_id.file_names.push_back(data_filename);
    current_id.start_reading_positions.push_back(start_position);
    current_id.end_reading_positions.push_back(end_position);
    reading_positions[id] = current_id;
}