ceph/src/boost/libs/iostreams/doc/guide/pipelines.html

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  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>
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  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'>&lt;boost/iostreams/concepts.hpp&gt;</SPAN></A>
  63 <SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/pipeline.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/pipeline.hpp&gt;</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>&lt;<SPAN CLASS="keyword">typename</SPAN> Source&gt;
  71     <SPAN CLASS="keyword">int</SPAN> get(Source&amp; 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'>&lt;boost/iostreams/filtering_stream.hpp&gt;</SPAN></A>
  82 <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>
  83 <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>
  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>&lt;boost/iostreams/pipeline.hpp&gt;</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>
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 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>)
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