[Discuss-gnuradio] A question about source code of the "File Source" Block

Hello

I am reading the source code of the "File Source" Block and have a question about the source code. In the source code, it firstly opens file by using the d_new_fp variable, then update by using the d_fp variable to replace it. Why not using the d_fp variable to open the file directly instead of replacing d_new_fp with d_fp. It confuses me. I will appreciate it If anyone knows that.

the source file including cpp and h is following:

file_source_impl.cc

/* -*- c++ -*- */
/*
 * Copyright 2012 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 *
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"