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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>

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<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&amp; 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>
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<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>)
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Commit	Line	Data
7c673cae FG	1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
	2	<HTML>
	3	<HEAD>
	4	<TITLE>Pipelines</TITLE>
	5	<LINK REL="stylesheet" HREF="../../../../boost.css">
	6	<LINK REL="stylesheet" HREF="../theme/iostreams.css">
	7	</HEAD>
	8	<BODY>
	9
	10	<!-- Begin Banner -->
	11
	12	<H1 CLASS="title">User's Guide</H1>
	13	<HR CLASS="banner">
	14
	15	<!-- End Banner -->
	16
	17	<!-- Begin Nav -->
	18
	19	<DIV CLASS='nav'>
	20	<A HREF='lifetimes.html'><IMG BORDER=0 WIDTH=19 HEIGHT=19 SRC='../../../../doc/src/images/prev.png'></A>
	21	<A HREF='guide.html'><IMG BORDER=0 WIDTH=19 HEIGHT=19 SRC='../../../../doc/src/images/up.png'></A>
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	23	</DIV>
	24
	25	<!-- End Nav -->
	26
	27	<H2>3.8 Pipelines</H2>
	28
	29	<DL class="page-index">
	30	<DT><A href="#overview">Overview</A></DT>
	31	<DT><A href="#examples">Examples</A></DT>
	32	<DT><A href="#headers">Headers</A></DT>
	33	<DT><A href="#reference">Reference</A></DT>
	34	</DL>
	35
	36	<HR STYLE="margin-top:1em">
	37
	38	<A NAME="overview"></A>
	39	<H2>Overview</H2>
	40
	41	<P>
	42	A pipeline is an expression of the form
	43	</P>
	44	<PRE CLASS="broken_ie">filter<SUB>1</SUB> \| ... \| filter<SUB>n</SUB> \| filter-or-device</PRE>
	45	<P>
	46	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>.
	47	</P>
	48
	49	<P>
	50	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>.
	51	</P>
	52
	53	<P>
	54	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>
	55	</P>
	56
	57	<A NAME="examples"></A>
	58	<H2>Examples</H2>
	59
	60	<P>The following example defines a <A HREF="../concepts/pipable.html">Pipable</A> InputFilter.</P>
	61
	62	<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>
	63	<SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/pipeline.hpp'><SPAN CLASS='literal'><boost/iostreams/pipeline.hpp></SPAN></A>
	64
65	<SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams;
66
67	<SPAN CLASS="keyword">class</SPAN> my_filter : <SPAN CLASS="keyword">public</SPAN> io::input_filter {
68	<SPAN CLASS="keyword">public:</SPAN>
69	<SPAN CLASS='omitted'>...</SPAN>
70	<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> Source>
71	<SPAN CLASS="keyword">int</SPAN> get(Source& src)
72	{
73	<SPAN CLASS='omitted'> ...</SPAN>
74	}
75	};
76	BOOST_IOSTREAMS_PIPABLE(my_filter, 0)
77	</PRE>
78
79	<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>
80
81	<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>
82	<SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/device/file.hpp'><SPAN CLASS='literal'><boost/iostreams/device/file.hpp></SPAN></A>
83	<SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filter/counter.hpp'><SPAN CLASS='literal'><boost/iostreams/filter/counter.hpp></SPAN></A>
84
85	<SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams;
86
87	<SPAN CLASS="keyword">int</SPAN> main()
88	{
89	<SPAN CLASS='comment'>// Write to the file "hello," counting</SPAN>
90	<SPAN CLASS='comment'>// the number of lines and characters</SPAN>
91	io::filtering_ostream out(io::counter() \| io::file("hello"));
92	<SPAN CLASS='omitted'>...</SPAN>
93	}</PRE>
94
95	<A NAME="headers"></A>
96	<H2>Headers</H2>
97
98	<DL class="page-index">
99	<DT><A CLASS="header" HREF="../../../../boost/iostreams/pipeline.hpp"><CODE><boost/iostreams/pipeline.hpp></CODE></A></DT>
100	</DL>
101
102	<A NAME="boost_iostreams_pipable"></A>
103	<A NAME="reference"></A>
104	<H2>Reference</H2>
105
106	<PRE CLASS="broken_ie">
107
108	<SPAN CLASS='preprocessor'>#define</SPAN> BOOST_IOSTREAMS_PIPABLE(filter, arity) <SPAN CLASS='omitted'>...</SPAN>
109
110	</PRE>
111
112	<H4>Description</H4>
113
114	<P>Defines the overloads of <CODE>operator\|</CODE> necessary for a <A HREF="../concepts/filter.html">Filter</A> to appear in pipelines.</P>
115
116	<A NAME="macro_params"></A>
117	<H4>Macro parameters</H4>
118
119	<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
120	<TR>
121	<TR>
122	<TD VALIGN="top"><I>filter</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
123	<TD>The name of the <A HREF="../concepts/filter.html">Filter</A> to be declared <A HREF="../concepts/pipable.html">Pipable</A></TD>
124	</TR>
125	<TR>
126	<TD VALIGN="top"><I>arity</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
127	<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>
128	</TR>
129	</TABLE>
130
131	<!-- Begin Footer -->
132
133	<HR STYLE="margin-top:1em">
134
135	<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>
136	<P CLASS="copyright">
137	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>)
138	</P>
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