<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML> <HEAD> <TITLE>Filtering Streams and Stream Buffers</TITLE> <LINK REL="stylesheet" href="../../../../boost.css"> <LINK REL="stylesheet" href="../theme/iostreams.css"> <STYLE> .caption_code { font: bold 8pt monospace } </STYLE> </HEAD> <BODY> <!-- Begin Banner --> <H1 CLASS="title">User's Guide</H1> <HR CLASS="banner"> <!-- End Banner --> <!-- Begin Nav --> <DIV CLASS='nav'> <A HREF='generic_streams.html'><IMG BORDER=0 WIDTH=19 HEIGHT=19 SRC='../../../../doc/src/images/prev.png'></A> <A HREF='guide.html'><IMG BORDER=0 WIDTH=19 HEIGHT=19 SRC='../../../../doc/src/images/up.png'></A> <A HREF='code_conversion.html'><IMG BORDER=0 WIDTH=19 HEIGHT=19 SRC='../../../../doc/src/images/next.png'></A> </DIV> <!-- End Nav --> <A NAME="overview"></A> <H2>3.4 Filtering Streams and Stream Buffers</H2> <HR STYLE="margin-top:1em"> <P> 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. </P> <P> 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>. </P> <P> 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. <!-- Begin Footer --> <HR STYLE="margin-top:1em"> <P CLASS="copyright">Revised 02 Feb 2008</P> <P CLASS="copyright">© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>© Copyright 2004-2007 <a href="http://www.coderage.com/turkanis/" target="_top">Jonathan Turkanis</a></P> <P CLASS="copyright"> 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>) </P> <!-- End Footer --> </BODY>