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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.

<H2>Headers</H2>

</DL>

<H2>Reference</H2>

<H4>Synopsis</H4>

<PRE CLASS="broken_ie">namespace boost { namespace iostreams {

template<typename <A CLASS='documented' HREF='#template_params'>Ch</A>, typename <A CLASS='documented' HREF='#template_params'>Alloc</A> = std::allocator<Ch> >

class <A CLASS='documented' HREF='#template_params'>basic_line_filter</A> {

public:

typedef Ch char_type;

typedef std::basic_string<

Ch,

std::char_traits<char_type>,

Alloc

> string_type;

typedef [implementation-defined] category;

protected:

basic_line_filter();

public:

virtual ~basic_line_filter();

private:

virtual string_type <A CLASS='documented' HREF='#do_filter'>do_filter</A>(const string_type& line) = 0;

};

typedef basic_line_filter<char> line_filter;

typedef basic_line_filter<wchar_t> wline_filter;

} } // End namespace boost::io</PRE>

<H4>Template parameters</H4>

<TR>

<TD>The <A HREF='../guide/traits.html#char_type'>character type</A></TD>

</TR>

<TR>

<TD VALIGN="top">Alloc</TD><TD WIDTH="2em" VALIGN="top">-</TD>

<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>

</TR>

</TABLE>

<H4><CODE>line_filter::do_filter</CODE></H4>

<PRE CLASS="broken_ie"> virtual string_type do_filter(const string_type& line) = 0;</PRE>

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>.

<H2>Example</H2>

The following example shows a <CODE>line_filter</CODE> which counts the number of lines which exceed a given length.

<PRE CLASS="broken_ie">#include <A CLASS='header' HREF='../../../../boost/iostreams/filter/line.hpp'><boost/iostreams/filter/line.hpp></A>

namespace io = boost::iostreams;

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class long_line_counter : public io::line_filter {

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public

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explicit long_line_counter(int max_length = 80)

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: max_(max_length), count_(0)

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{ }

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int count() const { return count_; }

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private:

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std::string do_filter(const std::string& line)

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{

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if (line.size() > max_)

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++count_;

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}

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int max_;

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int count_;

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};</PRE>

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<HR>

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© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a> © Copyright 2004-2007 <a href="http://www.coderage.com/turkanis/" target="_top">Jonathan Turkanis</a>

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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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