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) 2015-2019  Made to Order Software Corporation

  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

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