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| 30 | <A NAME="overview"></A> |
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| 31 | <H2>3.4 Filtering Streams and Stream Buffers</H2> |
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| 32 | |
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| 33 | <HR STYLE="margin-top:1em"> |
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| 34 | |
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| 35 | <P> |
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| 36 | The class templates <A href="../classes/filtering_streambuf.html"><CODE>filtering_streambuf</CODE></A> and <A href="../classes/filtering_stream.html"><CODE>filtering_stream</CODE></A> are the fundamental components provided by the Iostreams library for filtering data. Each <CODE>filtering_streambuf</CODE> or <CODE>filtering_stream</CODE> contains a chain of zero or more <A HREF="../concepts/filter.html">Filters</A> followed by an optional <A HREF="../concepts/device.html">Device</A>, accessed with an interface similar to that of <CODE>std::stack</CODE>. These chains are represented by of the class template <A HREF="../classes/chain.html"><CODE>chain</CODE></A>. If the chain ends with a Device it is called <SPAN CLASS="term">complete</SPAN> and may be used to perform i/o. |
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| 37 | </P> |
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| 38 | <P> |
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| 39 | The <A HREF="modes.html">mode</A> of each <CODE>stream_buffer</CODE> in the chain must refine the mode of the <CODE>filtering_streambuf</CODE> or <CODE>filtering_stream</CODE>. For example, one cannot use a Filter or Device having mode <A HREF="modes.html#output">output</A> with a <CODE>filtering_streambuf</CODE> having mode <A HREF="modes.html#input">input</A>. |
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| 40 | </P> |
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| 41 | <P> |
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| 42 | If a <CODE>filtering_streambuf</CODE> or <CODE>filtering_stream</CODE> has mode <A HREF="modes.html#input">input</A>, data flows from the chain's end to its beginning — starting at a <A href="../concepts/source.html">Source</A> and passing through zero or more <A href="../concepts/input_filter.html">InputFilters</A>. If it has mode <A HREF="modes.html#output">output</A>, data flows in the opposite direction — from the beginning of the chain, through zero or more <A href="../concepts/output_filter.html">OutputFilters</A>, towards <A href="../concepts/source.html">Sink</A> at the end of the chain. If a <CODE>filtering_streambuf</CODE> or <CODE>filtering_stream</CODE> performs both input and output, data flows in both directions. |
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| 47 | <P CLASS="copyright">Revised |
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| 48 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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| 49 | 20 May, 2004 |
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| 50 | <!--webbot bot="Timestamp" endspan i-checksum="38504" --> |
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| 51 | </P> |
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| 52 | |
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| 53 | <P CLASS="copyright">© Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P> |
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| 54 | <P CLASS="copyright"> |
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| 55 | Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>) |
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