1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4 <TITLE>Class Template basic_line_filter</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">Class Template <CODE>basic_line_filter</CODE></H1> 13 <HR CLASS="banner"> 14 15<!-- End Banner --> 16 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> 23 24<HR> 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><boost/iostreams/filter/line.hpp></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><<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< 52 Ch, 53 std::char_traits<char_type>, 54 Alloc 55 > 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& line) <SPAN CLASS='numeric_literal'>= 0</SPAN>; 63}; 64 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>; 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& 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'><boost/iostreams/filter/line.hpp></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& line) 109 { 110 <SPAN CLASS='keyword'>if</SPAN> (line.size() > max_) 111 ++count_; 112 } 113 <SPAN CLASS='keyword'>int</SPAN> max_; 114 <SPAN CLASS='keyword'>int</SPAN> count_; 115};</PRE> 116 117<!-- Begin Footer --> 118 119<HR> 120 121<P CLASS="copyright">© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>© Copyright 2004-2007 <a href="https://www.boost.org/users/people/jonathan_turkanis.html" target="_top">Jonathan Turkanis</a></P> 122<P CLASS="copyright"> 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>) 124</P> 125 126<!-- End Footer --> 127 128</BODY> 129