for (unsigned int i = 0; i < indexes[id].file_names.size(); i++) {
        const char* current_filename = indexes[id].file_names[i].c_str();
        long int start_reading_position = indexes[id].start_reading_positions[i];
        long int end_reading_position = indexes[id].end_reading_positions[i];
        size_t reading_bytes_number = static_cast<size_t>(end_reading_position - start_reading_position);
        data_file = fopen(current_filename, "a+b");
        void* current_read_data = malloc(reading_bytes_number);
        fseek(data_file, start_reading_position, 0);
        fread(current_read_data, 1, reading_bytes_number, data_file);
        memcpy((void*)((char*)return_data + (reading_bytes_number*i)), current_read_data, reading_bytes_number);
        free(current_read_data);
        fclose(data_file);
    }