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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>
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>
26 <A NAME="description"></A>
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.
33 <A NAME="headers"></A>
36 <DL class="page-index">
37 <DT><A CLASS="header" HREF="../../../../boost/iostreams/filter/line.hpp"><CODE><boost/iostreams/filter/line.hpp></CODE></A></DT>
40 <A NAME="reference"></A>
45 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
47 <SPAN CLASS='keyword'>template</SPAN><<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<Ch> >
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<
53 std::char_traits<char_type>,
56 <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN> category;
57 <SPAN CLASS='keyword'>protected:</SPAN>
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& line) <SPAN CLASS='numeric_literal'>= 0</SPAN>;
65 <SPAN CLASS='keyword'>typedef</SPAN> basic_line_filter<<SPAN CLASS='keyword'>char</SPAN>> <SPAN CLASS='defined'>line_filter</SPAN>;
66 <SPAN CLASS='keyword'>typedef</SPAN> basic_line_filter<<SPAN CLASS='keyword'>wchar_t</SPAN>> <SPAN CLASS='defined'>wline_filter</SPAN>;
68 } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
70 <A NAME="template_params"></A>
71 <H4>Template parameters</H4>
73 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
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>
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>
85 <A NAME="do_filter"></A>
86 <H4><CODE>line_filter::do_filter</CODE></H4>
88 <PRE CLASS="broken_ie"> <SPAN CLASS='keyword'>virtual</SPAN> string_type do_filter(<SPAN CLASS='keyword'>const</SPAN> string_type& line) <SPAN CLASS='numeric_literal'>= 0</SPAN>;</PRE>
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>
92 <A NAME="example"></A>
95 <P>The following example shows a <CODE>line_filter</CODE> which counts the number of lines which exceed a given length.</P>
97 <PRE CLASS="broken_ie"><SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filter/line.hpp'><SPAN CLASS='literal'><boost/iostreams/filter/line.hpp></SPAN></A>
99 <SPAN CLASS='keyword'>namespace</SPAN> io = boost::iostreams;
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>)
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& line)
110 <SPAN CLASS='keyword'>if</SPAN> (line.size() > max_)
113 <SPAN CLASS='keyword'>int</SPAN> max_;
114 <SPAN CLASS='keyword'>int</SPAN> count_;
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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>)