iostreams/device/null.hpp

0001 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
0002 // (C) Copyright 2004-2007 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 // Inspired by Daryle Walker's nullbuf from his More I/O submission.
0009
0010 #ifndef BOOST_IOSTREAMS_NULL_HPP_INCLUDED
0011 #define BOOST_IOSTREAMS_NULL_HPP_INCLUDED
0012
0013 #if defined(_MSC_VER)
0014 # pragma once
0015 #endif
0016
0017 #include <boost/iostreams/categories.hpp>
0018 #include <boost/iostreams/detail/ios.hpp> // openmode, streamsize.
0019 #include <boost/iostreams/positioning.hpp>
0020
0021 namespace boost { namespace iostreams {
0022
0023 template<typename Ch, typename Mode>
0024 class basic_null_device {
0025 public:
0026     typedef Ch char_type;
0027     struct category
0028         : public Mode,
0029           public device_tag,
0030           public closable_tag
0031         { };
0032     std::streamsize read(Ch*, std::streamsize) { return -1; }
0033     std::streamsize write(const Ch*, std::streamsize n) { return n; }
0034     std::streampos seek( stream_offset, BOOST_IOS::seekdir,
0035                          BOOST_IOS::openmode =
0036                              BOOST_IOS::in | BOOST_IOS::out )
0037     { return -1; }
0038     void close() { }
0039     void close(BOOST_IOS::openmode) { }
0040 };
0041
0042 template<typename Ch>
0043 struct basic_null_source : private basic_null_device<Ch, input> {
0044     typedef Ch          char_type;
0045     typedef source_tag  category;
0046     using basic_null_device<Ch, input>::read;
0047     using basic_null_device<Ch, input>::close;
0048 };
0049
0050 typedef basic_null_source<char>     null_source;
0051 typedef basic_null_source<wchar_t>  wnull_source;
0052
0053 template<typename Ch>
0054 struct basic_null_sink : private basic_null_device<Ch, output> {
0055     typedef Ch        char_type;
0056     typedef sink_tag  category;
0057     using basic_null_device<Ch, output>::write;
0058     using basic_null_device<Ch, output>::close;
0059 };
0060
0061 typedef basic_null_sink<char>     null_sink;
0062 typedef basic_null_sink<wchar_t>  wnull_sink;
0063
0064 } } // End namespaces iostreams, boost.
0065
0066 #endif // #ifndef BOOST_IOSTREAMS_NULL_HPP_INCLUDED