boost/iostreams/skip.hpp

   1 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
   2 // (C) Copyright 2003-2007 Jonathan Turkanis
   3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)
   5
   6 // See http://www.boost.org/libs/iostreams for documentation.
   7
   8 // To do: handle bidirection streams and output-seekable components.
   9
  10 #ifndef BOOST_IOSTREAMS_SKIP_HPP_INCLUDED
  11 #define BOOST_IOSTREAMS_SKIP_HPP_INCLUDED
  12
  13 #if defined(_MSC_VER) && (_MSC_VER >= 1020)
  14 # pragma once
  15 #endif
  16
  17 #include <boost/iostreams/char_traits.hpp>
  18 #include <boost/iostreams/detail/ios.hpp>  // failure.
  19 #include <boost/iostreams/operations.hpp>
  20 #include <boost/iostreams/seek.hpp>
  21 #include <boost/iostreams/traits.hpp>
  22 #include <boost/mpl/and.hpp>
  23 #include <boost/mpl/bool.hpp>
  24 #include <boost/mpl/or.hpp>
  25 #include <boost/type_traits/is_convertible.hpp>
  26
  27 namespace boost { namespace iostreams {
  28
  29 namespace detail {
  30
  31 template<typename Device>
  32 void skip(Device& dev, stream_offset off, mpl::true_)
  33 { iostreams::seek(dev, off, BOOST_IOS::cur); }
  34
  35 template<typename Device>
  36 void skip(Device& dev, stream_offset off, mpl::false_)
  37 {   // gcc 2.95 needs namespace qualification for char_traits.
  38     typedef typename char_type_of<Device>::type  char_type;
  39     typedef iostreams::char_traits<char_type>    traits_type;
  40     for (stream_offset z = 0; z < off; ) {
  41         typename traits_type::int_type c;
  42         if (traits_type::is_eof(c = iostreams::get(dev)))
  43             throw BOOST_IOSTREAMS_FAILURE("bad skip offset");
  44         if (!traits_type::would_block(c))
  45             ++z;
  46     }
  47 }
  48
  49 template<typename Filter, typename Device>
  50 void skip( Filter& flt, Device& dev, stream_offset off,
  51            BOOST_IOS::openmode which, mpl::true_ )
  52 { boost::iostreams::seek(flt, dev, off, BOOST_IOS::cur, which); }
  53
  54 template<typename Filter, typename Device>
  55 void skip( Filter& flt, Device& dev, stream_offset off,
  56            BOOST_IOS::openmode, mpl::false_ )
  57 {
  58     typedef typename char_type_of<Device>::type char_type;
  59     char_type c;
  60     for (stream_offset z = 0; z < off; ) {
  61         std::streamsize amt;
  62         if ((amt = iostreams::read(flt, dev, &c, 1)) == -1)
  63             throw BOOST_IOSTREAMS_FAILURE("bad skip offset");
  64         if (amt == 1)
  65             ++z;
  66     }
  67 }
  68
  69 } // End namespace detail.
  70
  71 template<typename Device>
  72 void skip(Device& dev, stream_offset off)
  73 {
  74     typedef typename mode_of<Device>::type     mode;
  75     typedef mpl::or_<
  76         is_convertible<mode, input_seekable>,
  77         is_convertible<mode, output_seekable>
  78     >                                          can_seek;
  79     BOOST_STATIC_ASSERT(
  80         (can_seek::value || is_convertible<mode, input>::value)
  81     );
  82     detail::skip(dev, off, can_seek());
  83 }
  84
  85 template<typename Filter, typename Device>
  86 void skip( Filter& flt, Device& dev, stream_offset off,
  87            BOOST_IOS::openmode which = BOOST_IOS::in | BOOST_IOS::out )
  88 {
  89     typedef typename mode_of<Filter>::type                 filter_mode;
  90     typedef typename mode_of<Device>::type                 device_mode;
  91     typedef mpl::or_<
  92         mpl::and_<
  93             is_convertible<filter_mode, input_seekable>,
  94             is_convertible<device_mode, input_seekable>
  95         >,
  96         mpl::and_<
  97             is_convertible<filter_mode, output_seekable>,
  98             is_convertible<device_mode, output_seekable>
  99         >
 100     >                                                      can_seek;
 101     BOOST_STATIC_ASSERT(
 102         ( can_seek::value ||
 103           is_convertible<filter_mode, input>::value &&
 104           is_convertible<device_mode, input>::value )
 105     );
 106     detail::skip(flt, dev, off, which, can_seek());
 107 }
 108
 109 } } // End namespaces iostreams, boost.
 110
 111 #endif // #ifndef BOOST_IOSTREAMS_SKIP_HPP_INCLUDED //------------------------//