ceph/src/boost/libs/iostreams/doc/classes/line_filter.html

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   4     <TITLE>Class Template basic_line_filter</TITLE>
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  12     <H1 CLASS="title">Class Template <CODE>basic_line_filter</CODE></H1>
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  17 <DL class="page-index">
  18   <DT><A href="#description">Description</A></DT>
  19   <DT><A href="#headers">Headers</A></DT>
  20   <DT><A href="#reference">Reference</A></DT>
  21   <DT><A href="#example">Example</A></DT>
  22 </DL>
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  25
  26 <A NAME="description"></A>
  27 <H2>Description</H2>
  28
  29 <P>
  30     The class template <CODE>basic_line_filter</CODE> is a <A HREF='../concepts/dual_use_filter.html'>DualUseFilter</A> for use as a base class by Filters which filter a character sequence one line at a time. Derived classes override the <CODE>private</CODE> <CODE>virtual</CODE> function <CODE>do_filter</CODE>, which takes a line of unfiltered text as argument returns the result of filtering the line.
  31 </P>
  32
  33 <A NAME="headers"></A>
  34 <H2>Headers</H2>
  35
  36 <DL class="page-index">
  37   <DT><A CLASS="header" HREF="../../../../boost/iostreams/filter/line.hpp"><CODE>&lt;boost/iostreams/filter/line.hpp&gt;</CODE></A></DT>
  38 </DL>
  39
  40 <A NAME="reference"></A>
  41 <H2>Reference</H2>
  42
  43 <H4>Synopsis</H4>
  44
  45 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
  46
  47 <SPAN CLASS='keyword'>template</SPAN>&lt;<SPAN CLASS='keyword'>typename</SPAN> <A CLASS='documented' HREF='#template_params'>Ch</A>, <SPAN CLASS='keyword'>typename</SPAN> <A CLASS='documented' HREF='#template_params'>Alloc</A> = std::allocator&lt;Ch&gt; &gt;
  48 <SPAN CLASS='keyword'>class</SPAN> <A CLASS='documented' HREF='#template_params'>basic_line_filter</A>  {
  49 <SPAN CLASS='keyword'>public:</SPAN>
  50     <SPAN CLASS='keyword'>typedef</SPAN> Ch                                char_type;
  51     <SPAN CLASS='keyword'>typedef</SPAN> std::basic_string&lt;
  52                 Ch,
  53                 std::char_traits&lt;char_type&gt;,
  54                 Alloc
  55             &gt;                                 string_type;
  56     <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>          category;
  57 <SPAN CLASS='keyword'>protected:</SPAN>
  58     basic_line_filter();
  59 <SPAN CLASS='keyword'>public:</SPAN>
  60     <SPAN CLASS='keyword'>virtual</SPAN> ~basic_line_filter();
  61 <SPAN CLASS='keyword'>private:</SPAN>
  62     <SPAN CLASS='keyword'>virtual</SPAN> string_type <A CLASS='documented' HREF='#do_filter'>do_filter</A>(<SPAN CLASS='keyword'>const</SPAN> string_type&amp; line) <SPAN CLASS='numeric_literal'>= 0</SPAN>;
  63 };
  64
  65 <SPAN CLASS='keyword'>typedef</SPAN> basic_line_filter&lt;<SPAN CLASS='keyword'>char</SPAN>&gt;     <SPAN CLASS='defined'>line_filter</SPAN>;
  66 <SPAN CLASS='keyword'>typedef</SPAN> basic_line_filter&lt;<SPAN CLASS='keyword'>wchar_t</SPAN>&gt;  <SPAN CLASS='defined'>wline_filter</SPAN>;
  67
  68 } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
  69
  70 <A NAME="template_params"></A>
  71 <H4>Template parameters</H4>
  72
  73 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
  74 <TR>
  75     <TR>
  76         <TD VALIGN="top"><I>Ch</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
  77         <TD>The <A HREF='../guide/traits.html#char_type'>character type</A></TD>
  78     </TR>
  79     <TR>
  80         <TD VALIGN="top"><I>Alloc</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
  81         <TD>A standard library allocator type (<A CLASS="bib_ref" HREF="../bibliography.html#iso">[ISO]</A>, 20.1.5), used to allocate a character buffer</TD>
  82     </TR>
  83 </TABLE>
  84
  85 <A NAME="do_filter"></A>
  86 <H4><CODE>line_filter::do_filter</CODE></H4>
  87
  88 <PRE CLASS="broken_ie">    <SPAN CLASS='keyword'>virtual</SPAN> string_type do_filter(<SPAN CLASS='keyword'>const</SPAN> string_type&amp; line) <SPAN CLASS='numeric_literal'>= 0</SPAN>;</PRE>
  89
  90 <P>The argument <CODE>line</CODE> represents a single line of unfiltered text, not including any terminal newline character. Returns the result of filtering <CODE>line</CODE>.</P>
  91
  92 <A NAME="example"></A>
  93 <H2>Example</H2>
  94
  95 <P>The following example shows a <CODE>line_filter</CODE> which counts the number of lines which exceed a given length.</P>
  96
  97 <PRE CLASS="broken_ie"><SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filter/line.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/filter/line.hpp&gt;</SPAN></A>
  98
  99 <SPAN CLASS='keyword'>namespace</SPAN> io = boost::iostreams;
 100
 101 <SPAN CLASS='keyword'>class</SPAN> long_line_counter : <SPAN CLASS='keyword'>public</SPAN> io::line_filter {
 102 <SPAN CLASS='keyword'>public</SPAN>
 103     <SPAN CLASS="keyword">explicit</SPAN> long_line_counter(<SPAN CLASS='keyword'>int</SPAN> max_length = <SPAN CLASS='numeric_literal'>80</SPAN>)
 104         : max_(max_length), count_(<SPAN CLASS='numeric_literal'>0</SPAN>)
 105         { }
 106     <SPAN CLASS='keyword'>int</SPAN> count() <SPAN CLASS='keyword'>const</SPAN> { <SPAN CLASS='keyword'>return</SPAN> count_; }
 107 <SPAN CLASS='keyword'>private:</SPAN>
 108     std::string do_filter(<SPAN CLASS='keyword'>const</SPAN> std::string&amp; line)
 109     {
 110         <SPAN CLASS='keyword'>if</SPAN> (line.size() &gt; max_)
 111             ++count_;
 112     }
 113     <SPAN CLASS='keyword'>int</SPAN> max_;
 114     <SPAN CLASS='keyword'>int</SPAN> count_;
 115 };</PRE>
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 123     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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