| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
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| 2 | <HTML> |
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| 3 | <HEAD> |
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| 4 | <TITLE>Pipelines</TITLE> |
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| 5 | <LINK REL="stylesheet" HREF="../../../../boost.css"> |
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| 6 | <LINK REL="stylesheet" HREF="../theme/iostreams.css"> |
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| 7 | </HEAD> |
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| 8 | <BODY> |
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| 9 | |
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| 10 | <!-- Begin Banner --> |
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| 11 | |
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| 12 | <H1 CLASS="title">User's Guide</H1> |
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| 13 | <HR CLASS="banner"> |
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| 14 | |
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| 15 | <!-- End Banner --> |
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| 16 | |
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| 17 | <!-- Begin Nav --> |
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| 18 | |
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| 19 | <DIV CLASS='nav'> |
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| 20 | <A HREF='lifetimes.html'><IMG BORDER=0 WIDTH=19 HEIGHT=19 SRC='../../../../doc/html/images/prev.png'></A> |
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| 23 | </DIV> |
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| 24 | |
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| 25 | <!-- End Nav --> |
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| 26 | |
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| 27 | <A NAME="overview"></A> |
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| 28 | <H2>3.8 Pipelines</H2> |
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| 29 | |
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| 30 | <DL class="page-index"> |
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| 31 | <DT><A href="#overview">Overview</A></DT> |
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| 32 | <DT><A href="#examples">Examples</A></DT> |
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| 33 | <DT><A href="#headers">Headers</A></DT> |
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| 34 | <DT><A href="#reference">Reference</A></DT> |
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| 35 | </DL> |
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| 36 | |
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| 37 | <HR STYLE="margin-top:1em"> |
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| 38 | |
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| 39 | <A NAME="overview"></A> |
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| 40 | <H2>Overview</H2> |
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| 41 | |
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| 42 | <P> |
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| 43 | A pipeline is an expression of the form |
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| 44 | </P> |
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| 45 | <PRE CLASS="broken_ie">filter<SUB>1</SUB> | ... | filter<SUB>n</SUB> | filter-or-device</PRE> |
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| 46 | <P> |
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| 47 | 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>. |
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| 48 | </P> |
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| 49 | |
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| 50 | <P> |
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| 51 | 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>. |
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| 52 | </P> |
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| 53 | |
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| 54 | <P> |
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| 55 | 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> |
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| 56 | </P> |
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| 57 | |
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| 58 | <A NAME="examples"></A> |
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| 59 | <H2>Examples</H2> |
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| 60 | |
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| 61 | <P>The following example defines a <A HREF="../concepts/pipable.html">Pipable</A> InputFilter.</P> |
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| 62 | |
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| 63 | <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> |
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| 64 | <SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/pipeline.hpp'><SPAN CLASS='literal'><boost/iostreams/pipeline.hpp></SPAN></A> |
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| 65 | |
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| 66 | <SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams; |
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| 67 | |
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| 68 | <SPAN CLASS="keyword">class</SPAN> my_filter : <SPAN CLASS="keyword">public</SPAN> io::input_filter { |
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| 69 | <SPAN CLASS="keyword">public:</SPAN> |
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| 70 | <SPAN CLASS='omitted'>...</SPAN> |
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| 71 | <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> Source> |
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| 72 | <SPAN CLASS="keyword">int</SPAN> get(Source& src) |
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| 73 | { |
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| 74 | <SPAN CLASS='omitted'> ...</SPAN> |
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| 75 | } |
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| 76 | }; |
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| 77 | BOOST_IOSTREAMS_PIPABLE(my_filter, 0) |
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| 78 | </PRE> |
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| 79 | |
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| 80 | <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> |
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| 81 | |
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| 82 | <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> |
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| 83 | <SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/device/file.hpp'><SPAN CLASS='literal'><boost/iostreams/device/file.hpp></SPAN></A> |
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| 84 | <SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filter/counter.hpp'><SPAN CLASS='literal'><boost/iostreams/filter/counter.hpp></SPAN></A> |
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| 85 | |
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| 86 | <SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams; |
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| 87 | |
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| 88 | <SPAN CLASS="keyword">int</SPAN> main() |
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| 89 | { |
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| 90 | <SPAN CLASS='comment'>// Write to the file "hello," counting</SPAN> |
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| 91 | <SPAN CLASS='comment'>// the number of lines and characters</SPAN> |
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| 92 | io::filtering_ostream out(io::counter() | io::file("hello")); |
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| 93 | <SPAN CLASS='omitted'>...</SPAN> |
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| 94 | }</PRE> |
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| 95 | |
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| 96 | <A NAME="headers"></A> |
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| 97 | <H2>Headers</H2> |
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| 98 | |
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| 99 | <DL class="page-index"> |
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| 100 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/pipeline.hpp"><CODE><boost/iostreams/pipeline.hpp></CODE></A></DT> |
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| 101 | </DL> |
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| 102 | |
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| 103 | <A NAME="boost_iostreams_pipable"></A> |
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| 104 | <A NAME="reference"></A> |
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| 105 | <H2>Reference</H2> |
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| 106 | |
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| 107 | <PRE CLASS="broken_ie"> |
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| 108 | |
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| 109 | <SPAN CLASS='preprocessor'>#define</SPAN> BOOST_IOSTREAMS_PIPABLE(filter, arity) <SPAN CLASS='omitted'>...</SPAN> |
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| 110 | |
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| 111 | </PRE> |
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| 112 | |
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| 113 | <H4>Description</H4> |
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| 114 | |
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| 115 | <P>Defines the overloads of <CODE>operator|</CODE> necessary for a <A HREF="../concepts/filter.html">Filter</A> to appear in pipelines.</P> |
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| 116 | |
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| 117 | <A NAME="macro_params"></A> |
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| 118 | <H4>Macro parameters</H4> |
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| 119 | |
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| 120 | <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> |
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| 121 | <TR> |
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| 122 | <TR> |
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| 123 | <TD VALIGN="top"><I>filter</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> |
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| 124 | <TD>The name of the <A HREF="../concepts/filter.html">Filter</A> to be declared <A HREF="../concepts/pipable.html">Pipable</A></TD> |
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| 125 | </TR> |
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| 126 | <TR> |
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| 127 | <TD VALIGN="top"><I>arity</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> |
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| 128 | <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> |
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| 129 | </TR> |
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| 130 | </TABLE> |
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| 131 | |
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| 132 | <!-- Begin Footer --> |
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| 133 | |
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| 134 | <HR STYLE="margin-top:1em"> |
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| 135 | <P CLASS="copyright">Revised |
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| 136 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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| 137 | 20 May, 2004 |
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| 138 | <!--webbot bot="Timestamp" endspan i-checksum="38504" --> |
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| 139 | </P> |
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| 140 | |
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| 141 | <P CLASS="copyright">© Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P> |
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| 142 | <P CLASS="copyright"> |
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| 143 | 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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| 144 | </P> |
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| 146 | <!-- End Footer --> |
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