boost/iostreams/skip.hpp

0001 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
0002 // (C) Copyright 2003-2007 Jonathan Turkanis
0003 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0004 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)
0005
0006 // See http://www.boost.org/libs/iostreams for documentation.
0007
0008 // To do: handle bidirection streams and output-seekable components.
0009
0010 #ifndef BOOST_IOSTREAMS_SKIP_HPP_INCLUDED
0011 #define BOOST_IOSTREAMS_SKIP_HPP_INCLUDED
0012
0013 #if defined(_MSC_VER)
0014 # pragma once
0015 #endif
0016
0017 #include <boost/iostreams/char_traits.hpp>
0018 #include <boost/iostreams/detail/ios.hpp>  // failure.
0019 #include <boost/iostreams/operations.hpp>
0020 #include <boost/iostreams/seek.hpp>
0021 #include <boost/iostreams/traits.hpp>
0022 #include <boost/mpl/and.hpp>
0023 #include <boost/mpl/bool.hpp>
0024 #include <boost/mpl/or.hpp>
0025 #include <boost/throw_exception.hpp>
0026 #include <boost/type_traits/is_convertible.hpp>
0027
0028 namespace boost { namespace iostreams {
0029
0030 namespace detail {
0031
0032 template<typename Device>
0033 void skip(Device& dev, stream_offset off, mpl::true_)
0034 { iostreams::seek(dev, off, BOOST_IOS::cur); }
0035
0036 template<typename Device>
0037 void skip(Device& dev, stream_offset off, mpl::false_)
0038 {   // gcc 2.95 needs namespace qualification for char_traits.
0039     typedef typename char_type_of<Device>::type  char_type;
0040     typedef iostreams::char_traits<char_type>    traits_type;
0041     for (stream_offset z = 0; z < off; ) {
0042         typename traits_type::int_type c;
0043         if (traits_type::is_eof(c = iostreams::get(dev)))
0044             boost::throw_exception(BOOST_IOSTREAMS_FAILURE("bad skip offset"));
0045         if (!traits_type::would_block(c))
0046             ++z;
0047     }
0048 }
0049
0050 template<typename Filter, typename Device>
0051 void skip( Filter& flt, Device& dev, stream_offset off,
0052            BOOST_IOS::openmode which, mpl::true_ )
0053 { boost::iostreams::seek(flt, dev, off, BOOST_IOS::cur, which); }
0054
0055 template<typename Filter, typename Device>
0056 void skip( Filter& flt, Device& dev, stream_offset off,
0057            BOOST_IOS::openmode, mpl::false_ )
0058 {
0059     typedef typename char_type_of<Device>::type char_type;
0060     char_type c;
0061     for (stream_offset z = 0; z < off; ) {
0062         std::streamsize amt;
0063         if ((amt = iostreams::read(flt, dev, &c, 1)) == -1)
0064             boost::throw_exception(BOOST_IOSTREAMS_FAILURE("bad skip offset"));
0065         if (amt == 1)
0066             ++z;
0067     }
0068 }
0069
0070 } // End namespace detail.
0071
0072 template<typename Device>
0073 void skip(Device& dev, stream_offset off)
0074 {
0075     typedef typename mode_of<Device>::type     mode;
0076     typedef mpl::or_<
0077         is_convertible<mode, input_seekable>,
0078         is_convertible<mode, output_seekable>
0079     >                                          can_seek;
0080     BOOST_STATIC_ASSERT(
0081         (can_seek::value || is_convertible<mode, input>::value)
0082     );
0083     detail::skip(dev, off, can_seek());
0084 }
0085
0086 template<typename Filter, typename Device>
0087 void skip( Filter& flt, Device& dev, stream_offset off,
0088            BOOST_IOS::openmode which = BOOST_IOS::in | BOOST_IOS::out )
0089 {
0090     typedef typename mode_of<Filter>::type                 filter_mode;
0091     typedef typename mode_of<Device>::type                 device_mode;
0092     typedef mpl::or_<
0093         mpl::and_<
0094             is_convertible<filter_mode, input_seekable>,
0095             is_convertible<device_mode, input_seekable>
0096         >,
0097         mpl::and_<
0098             is_convertible<filter_mode, output_seekable>,
0099             is_convertible<device_mode, output_seekable>
0100         >
0101     >                                                      can_seek;
0102     BOOST_STATIC_ASSERT(
0103         ( can_seek::value ||
0104           (is_convertible<filter_mode, input>::value &&
0105           is_convertible<device_mode, input>::value) )
0106     );
0107     detail::skip(flt, dev, off, which, can_seek());
0108 }
0109
0110 } } // End namespaces iostreams, boost.
0111
0112 #endif // #ifndef BOOST_IOSTREAMS_SKIP_HPP_INCLUDED //------------------------//