virtualseeker.cpp

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/*
  Zipios -- a small C++ library that provides easy access to .zip files.
 
  Copyright (C) 2000-2007  Thomas Sondergaard
  Copyright (c) 2015-2022  Made to Order Software Corp.  All Rights Reserved
 
  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.
 
  This library 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
  Lesser General Public License for more details.
 
  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/
 
#include "zipios/virtualseeker.hpp"
 
#include "zipios/zipiosexceptions.hpp"
 
 
namespace zipios
{
 
 
VirtualSeeker::VirtualSeeker(offset_t start_offset, offset_t end_offset)
    : m_start_offset(start_offset)
    , m_end_offset(end_offset)
{
    if(m_start_offset < 0
    || m_end_offset < 0)
    {
        throw InvalidException("VirtualSeeker::VirtualSeeker(): the start and end offsets cannot be negative.");
    }
}
 
 
void VirtualSeeker::setOffsets(offset_t start_offset, offset_t end_offset)
{
    if(start_offset < 0
    || end_offset < 0)
    {
        throw InvalidException("VirtualSeeker::VirtualSeeker(): the start and end offsets cannot be negative.");
    }
 
    m_start_offset = start_offset;
    m_end_offset = end_offset;
}
 
 
void VirtualSeeker::getOffsets(offset_t & start_offset, offset_t & end_offset) const
{
    start_offset = m_start_offset;
    end_offset = m_end_offset;
}
 
 
offset_t VirtualSeeker::startOffset() const
{
    return m_start_offset;
}
 
 
offset_t VirtualSeeker::endOffset() const
{
    return m_end_offset;
}
 
 
void VirtualSeeker::vseekg(std::istream &is, offset_t offset, std::ios::seekdir sd) const
{
    switch(sd)
    {
    case std::ios::cur:
        break;
 
    case std::ios::beg:
        offset += m_start_offset;
        break;
 
    case std::ios::end:
        // This definitively looks weird because this class makes use
        // of a POSITIVE offset from the end of the file as the end
        // offset. The parameter 'offset' is expected to be negative
        // or zero in this case.
        offset -= m_end_offset;
        break;
 
    default:
        throw std::logic_error("VirtualSeekManager::vseekg(): error - unknown seekdir");
 
    }
 
    is.seekg(offset, sd);
}
 
 
std::streampos VirtualSeeker::vtellg(std::istream & is) const
{
    return is.tellg() - m_start_offset;
}
 
 
} // zipios namespace
 
// Local Variables:
// mode: cpp
// indent-tabs-mode: nil
// c-basic-offset: 4
// tab-width: 4
// End:
 
// vim: ts=4 sw=4 et