boost/iostreams/device/null.hpp

   1 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
   2 // (C) Copyright 2004-2007 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 // Inspired by Daryle Walker's nullbuf from his More I/O submission.
   9
  10 #ifndef BOOST_IOSTREAMS_NULL_HPP_INCLUDED
  11 #define BOOST_IOSTREAMS_NULL_HPP_INCLUDED
  12
  13 #if defined(_MSC_VER) && (_MSC_VER >= 1020)
  14 # pragma once
  15 #endif
  16
  17 #include <boost/iostreams/categories.hpp>
  18 #include <boost/iostreams/detail/ios.hpp> // openmode, streamsize.
  19 #include <boost/iostreams/positioning.hpp>
  20
  21 namespace boost { namespace iostreams {
  22
  23 template<typename Ch, typename Mode>
  24 class basic_null_device {
  25 public:
  26     typedef Ch char_type;
  27     struct category
  28         : public Mode,
  29           public device_tag,
  30           public closable_tag
  31         { };
  32     std::streamsize read(Ch*, std::streamsize) { return 0; }
  33     std::streamsize write(const Ch*, std::streamsize n) { return n; }
  34     std::streampos seek( stream_offset, BOOST_IOS::seekdir,
  35                          BOOST_IOS::openmode =
  36                              BOOST_IOS::in | BOOST_IOS::out )
  37     { return -1; }
  38     void close() { }
  39     void close(BOOST_IOS::openmode) { }
  40 };
  41
  42 template<typename Ch>
  43 struct basic_null_source : private basic_null_device<Ch, input> {
  44     typedef Ch          char_type;
  45     typedef source_tag  category;
  46     using basic_null_device<Ch, input>::read;
  47     using basic_null_device<Ch, input>::close;
  48 };
  49
  50 typedef basic_null_source<char>     null_source;
  51 typedef basic_null_source<wchar_t>  wnull_source;
  52
  53 template<typename Ch>
  54 struct basic_null_sink : private basic_null_device<Ch, output> {
  55     typedef Ch        char_type;
  56     typedef sink_tag  category;
  57     using basic_null_device<Ch, output>::write;
  58     using basic_null_device<Ch, output>::close;
  59 };
  60
  61 typedef basic_null_sink<char>     null_sink;
  62 typedef basic_null_sink<wchar_t>  wnull_sink;
  63
  64 } } // End namespaces iostreams, boost.
  65
  66 #endif // #ifndef BOOST_IOSTREAMS_NULL_HPP_INCLUDED