Null Devices

Overview

Acknowledgments

Headers

Reference

Class template basic_null_source

Class template basic_null_sink

Class template basic_null_device

Overview

The class templates basic_null_source, basic_null_sink and basic_null_device are models of Device whose member functions all have trivial implementations. A basic_null_source is a Source whose member function read returns -1, indicating end-of-sequence. A basic_null_sink is a Sink whose member function write consumes and ignores the characters passed to it. A basic_null_device combines — depending on its template parameter Mode — the trivial read and write functions just described with a member seek that always returns an invalid stream position.

In addition, each of the above templates is Closable, with a no-op implementation of close.

Acknowledgments

The templates described here were inspired by Daryle Walker's basic_nullbuf template. See Disconnected Streams.

Headers

<boost/iostreams/device/null.hpp>

Reference

Class template basic_null_source

Description

Model of Source whose member function read returns -1, indicating end-of-sequence.

Synopsis

namespace boost { namespace iostreams {

template<typename Ch>
class basic_null_source { 
public:
    typedef Ch                        char_type;
    typedef [implementation-defined]  category;

    basic_null_source();    
    std::streamsize read(char_type* s, std::streamsize n);
    void close();
};

typedef basic_null_source<char>     null_source;
typedef basic_null_source<wchar_t>  wnull_source;

} } // End namespace boost::io

Template parameters

basic_null_source::basic_null_source

    basic_null_source();

Constructs a basic_null_source.

basic_null_source::read

    std::streamsize read(char_type* s, std::streamsize n);

Returns -1.

basic_null_source::close

    void close();

No-op.

Class template basic_null_sink

Description

Model of Sink whose member function write consumes and ignores the contents of the character buffer passed to it.

Synopsis

namespace boost { namespace iostreams {

template<typename Ch>
class basic_null_sink { 
public:
    typedef Ch                        char_type;
    typedef [implementation-defined]  category;

    basic_null_sink();
    std::streamsize write(const char_type* s, std::streamsize n);
    void close();
};

typedef basic_null_sink<char>     null_sink;
typedef basic_null_sink<wchar_t>  wnull_sink;

} } // End namespace boost::io

Template parameters

basic_null_sink::basic_null_sink

    basic_null_sink();

Constructs a basic_null_sink.

basic_null_sink::write

    std::streamsize write(const char_type* s, std::streamsize n);

Returns n.

basic_null_sink::close

    void close();

No-op.

Class template basic_null_device

Description

Model of Device whose mode is specified as a template parameter, and whose member functions have trivial implementations, as follows:

• read returns -1, indicating end-of-sequence
• write consumes but ignores the entire contents of the character buffer passed to it
• seek consumes but ignores the entire contents of the character buffer passed to it

Synopsis

namespace boost { namespace iostreams {

template<typename Ch, typename Mode>
class basic_null_device {
public:    
    typedef Ch                        char_type;
    typedef [implementation-defined]  category;

    basic_null_device();
    std::streamsize read(char_type* s, std::streamsize n);
    std::streamsize write(const char_type* s, std::streamsize n);
    stream_offset seek( stream_offset off, std::ios_base::seekdir way,
                        std::ios_base::openmode which =
                            std::ios_base::in | std::ios_base::out );
    void close();
};

} } // End namespace boost::io

Template parameters

basic_null_device::basic_null_device

    basic_null_device();

Constructs a basic_null_device.

basic_null_device::read

    std::streamsize read(char_type* s, std::streamsize n);

Returns -1. Enabled if Mode refines input.

basic_null_device::write

    std::streamsize write(const char_type* s, std::streamsize n);

Returns n. Enabled if Mode refines output.

basic_null_device::seek

     stream_offset seek( stream_offset off, std::ios_base::seekdir way,
                         std::ios_base::openmode which =
                             std::ios_base::in | std::ios_base::out );

Returns an invalid stream position. Enabled if Mode permits random access.

basic_null_device::close

    void close();

No-op.

Revised 20 May, 2004

© Copyright Jonathan Turkanis, 2004

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)