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 <H2>3.8 Pipelines</H2>

 <DL class="page-index">
   <DT><A href="#overview">Overview</A></DT>
   <DT><A href="#examples">Examples</A></DT>
   <DT><A href="#headers">Headers</A></DT>
   <DT><A href="#reference">Reference</A></DT>
 </DL>

 <HR STYLE="margin-top:1em">

 <A NAME="overview"></A>
 <H2>Overview</H2>

 <P>
     A pipeline is an expression of the form
 </P>
 <PRE CLASS="broken_ie">filter<SUB>1</SUB> | ... | filter<SUB>n</SUB> | filter-or-device</PRE>
 <P>
 consiting of one or more filters and an optional device, joined using <CODE>operator|</CODE>. Pipelines are a convenient way to pass chains of Filters and Devices to the constructor or <CODE>push</CODE> function of a <A HREF="../classes/filtering_stream.html"><CODE>filtering_stream</CODE></A> or <A HREF="../classes/filtering_streambuf.html"><CODE>filtering_streambuf</CODE></A>.
 </P>

 <P>
     In order for instances of a model of Filter to appear in a pipeline, it must be declared <A HREF="../concepts/pipable.html">Pipable</A> using the macro <A HREF="#boost_iostreams_pipable"><CODE>BOOST_IOSTREAMS_PIPABLE</CODE></A>.
 </P>

 <P>
    Pipelines for C++ filtering were introduced by Jan Christiaan van Winkel and John van Krieken. <I>See</I> <A CLASS="bib_ref" HREF="../bibliography.html#van_winkel">[van Winkel].</A>
 </P>

 <A NAME="examples"></A>
 <H2>Examples</H2>

 <P>The following example defines a <A HREF="../concepts/pipable.html">Pipable</A> InputFilter.</P>

 <PRE CLASS="broken_ie"><SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/concepts.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/concepts.hpp&gt;</SPAN></A>
 <SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/pipeline.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/pipeline.hpp&gt;</SPAN></A>

 <SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams;

 <SPAN CLASS="keyword">class</SPAN> my_filter : <SPAN CLASS="keyword">public</SPAN> io::input_filter {
 <SPAN CLASS="keyword">public:</SPAN>
     <SPAN CLASS='omitted'>...</SPAN>
     <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Source&gt;
     <SPAN CLASS="keyword">int</SPAN> get(Source& src)
     {
        <SPAN CLASS='omitted'> ...</SPAN>
     }
 };
 BOOST_IOSTREAMS_PIPABLE(my_filter, 0)
 </PRE>

 <P>No semicolon is required (or allowed) following the macro invocation. The following example shows a <A HREF="../classes/filtering_stream.html"><CODE>filtering_stream</CODE></A> constructed from a pipeline</CODE>.</P>

 <PRE CLASS="broken_ie"><SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filtering_stream.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/filtering_stream.hpp&gt;</SPAN></A>
 <SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/device/file.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/device/file.hpp&gt;</SPAN></A>
 <SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filter/counter.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/filter/counter.hpp&gt;</SPAN></A>

 <SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams;

 <SPAN CLASS="keyword">int</SPAN> main()
 {
     <SPAN CLASS='comment'>// Write to the file "hello," counting</SPAN>
     <SPAN CLASS='comment'>// the number of lines and characters</SPAN>
     io::filtering_ostream out(io::counter() | io::file("hello"));
     <SPAN CLASS='omitted'>...</SPAN>
 }</PRE>

 <A NAME="headers"></A>
 <H2>Headers</H2>

 <DL class="page-index">
   <DT><A CLASS="header" HREF="../../../../boost/iostreams/pipeline.hpp"><CODE>&lt;boost/iostreams/pipeline.hpp&gt;</CODE></A></DT>
 </DL>

 <A NAME="boost_iostreams_pipable"></A>
 <A NAME="reference"></A>
 <H2>Reference</H2>

 <PRE CLASS="broken_ie">

 <SPAN CLASS='preprocessor'>#define</SPAN> BOOST_IOSTREAMS_PIPABLE(filter, arity) <SPAN CLASS='omitted'>...</SPAN>

 </PRE>

 <H4>Description</H4>

 <P>Defines the overloads of <CODE>operator|</CODE> necessary for a <A HREF="../concepts/filter.html">Filter</A> to appear in pipelines.</P>

 <A NAME="macro_params"></A>
 <H4>Macro parameters</H4>

 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
 <TR>
     <TR>
         <TD VALIGN="top"><I>filter</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
         <TD>The name of the <A HREF="../concepts/filter.html">Filter</A> to be declared <A HREF="../concepts/pipable.html">Pipable</A></TD>
     </TR>
     <TR>
         <TD VALIGN="top"><I>arity</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
         <TD>The <A HREF="../concepts/filter.html">Filter</A>'s template arity, <I>i.e.</I>, the number or its template parameters; a value of <CODE>0</CODE> indicates that it is not a class template</TD>
     </TR>
 </TABLE>

 <!-- Begin Footer -->

 <HR STYLE="margin-top:1em">
 <P CLASS="copyright">Revised 02 Feb 2008</P>

 <P CLASS="copyright">&copy; Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>&copy; 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>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
	<HTML>
	<HEAD>
	<TITLE>Pipelines</TITLE>
	<LINK REL="stylesheet" HREF="../../../../boost.css">
	<LINK REL="stylesheet" HREF="../theme/iostreams.css">
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	<H2>3.8 Pipelines</H2>

	<DL class="page-index">
	<DT><A href="#overview">Overview</A></DT>
	<DT><A href="#examples">Examples</A></DT>
	<DT><A href="#headers">Headers</A></DT>
	<DT><A href="#reference">Reference</A></DT>
	</DL>

	<HR STYLE="margin-top:1em">

	<A NAME="overview"></A>
	<H2>Overview</H2>

	<P>
	A pipeline is an expression of the form
	</P>
	<PRE CLASS="broken_ie">filter<SUB>1</SUB> \| ... \| filter<SUB>n</SUB> \| filter-or-device</PRE>
	<P>
	consiting of one or more filters and an optional device, joined using <CODE>operator\|</CODE>. Pipelines are a convenient way to pass chains of Filters and Devices to the constructor or <CODE>push</CODE> function of a <A HREF="../classes/filtering_stream.html"><CODE>filtering_stream</CODE></A> or <A HREF="../classes/filtering_streambuf.html"><CODE>filtering_streambuf</CODE></A>.
	</P>

	<P>
	In order for instances of a model of Filter to appear in a pipeline, it must be declared <A HREF="../concepts/pipable.html">Pipable</A> using the macro <A HREF="#boost_iostreams_pipable"><CODE>BOOST_IOSTREAMS_PIPABLE</CODE></A>.
	</P>

	<P>
	Pipelines for C++ filtering were introduced by Jan Christiaan van Winkel and John van Krieken. <I>See</I> <A CLASS="bib_ref" HREF="../bibliography.html#van_winkel">[van Winkel].</A>
	</P>

	<A NAME="examples"></A>
	<H2>Examples</H2>

	<P>The following example defines a <A HREF="../concepts/pipable.html">Pipable</A> InputFilter.</P>

	<PRE CLASS="broken_ie"><SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/concepts.hpp'><SPAN CLASS='literal'><boost/iostreams/concepts.hpp></SPAN></A>
	<SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/pipeline.hpp'><SPAN CLASS='literal'><boost/iostreams/pipeline.hpp></SPAN></A>

	<SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams;

	<SPAN CLASS="keyword">class</SPAN> my_filter : <SPAN CLASS="keyword">public</SPAN> io::input_filter {
	<SPAN CLASS="keyword">public:</SPAN>
	<SPAN CLASS='omitted'>...</SPAN>
	<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> Source>
	<SPAN CLASS="keyword">int</SPAN> get(Source& src)
	{
	<SPAN CLASS='omitted'> ...</SPAN>
	}
	};
	BOOST_IOSTREAMS_PIPABLE(my_filter, 0)
	</PRE>

	<P>No semicolon is required (or allowed) following the macro invocation. The following example shows a <A HREF="../classes/filtering_stream.html"><CODE>filtering_stream</CODE></A> constructed from a pipeline</CODE>.</P>

	<PRE CLASS="broken_ie"><SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filtering_stream.hpp'><SPAN CLASS='literal'><boost/iostreams/filtering_stream.hpp></SPAN></A>
	<SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/device/file.hpp'><SPAN CLASS='literal'><boost/iostreams/device/file.hpp></SPAN></A>
	<SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filter/counter.hpp'><SPAN CLASS='literal'><boost/iostreams/filter/counter.hpp></SPAN></A>

	<SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams;

	<SPAN CLASS="keyword">int</SPAN> main()
	{
	<SPAN CLASS='comment'>// Write to the file "hello," counting</SPAN>
	<SPAN CLASS='comment'>// the number of lines and characters</SPAN>
	io::filtering_ostream out(io::counter() \| io::file("hello"));
	<SPAN CLASS='omitted'>...</SPAN>
	}</PRE>

	<A NAME="headers"></A>
	<H2>Headers</H2>

	<DL class="page-index">
	<DT><A CLASS="header" HREF="../../../../boost/iostreams/pipeline.hpp"><CODE><boost/iostreams/pipeline.hpp></CODE></A></DT>
	</DL>

	<A NAME="boost_iostreams_pipable"></A>
	<A NAME="reference"></A>
	<H2>Reference</H2>

	<PRE CLASS="broken_ie">

	<SPAN CLASS='preprocessor'>#define</SPAN> BOOST_IOSTREAMS_PIPABLE(filter, arity) <SPAN CLASS='omitted'>...</SPAN>

	</PRE>

	<H4>Description</H4>

	<P>Defines the overloads of <CODE>operator\|</CODE> necessary for a <A HREF="../concepts/filter.html">Filter</A> to appear in pipelines.</P>

	<A NAME="macro_params"></A>
	<H4>Macro parameters</H4>

	<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
	<TR>
	<TR>
	<TD VALIGN="top"><I>filter</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
	<TD>The name of the <A HREF="../concepts/filter.html">Filter</A> to be declared <A HREF="../concepts/pipable.html">Pipable</A></TD>
	</TR>
	<TR>
	<TD VALIGN="top"><I>arity</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
	<TD>The <A HREF="../concepts/filter.html">Filter</A>'s template arity, <I>i.e.</I>, the number or its template parameters; a value of <CODE>0</CODE> indicates that it is not a class template</TD>
	</TR>
	</TABLE>

	<!-- 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>