Class Template `basic_line_filter`

Description
Headers
Reference
Example

Description

The class template basic_line_filter is a DualUseFilter for use as a base class by Filters which filter a character sequence one line at a time. Derived classes override the private virtual function do_filter, which takes a line of unfiltered text as argument returns the result of filtering the line.

Headers

<boost/iostreams/filter/line.hpp>

Reference

Synopsis

namespace boost { namespace iostreams {

template<typename Ch, typename Alloc = std::allocator<Ch> >
class basic_line_filter  {
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 do_filter(const string_type& line) = 0;
};

typedef basic_line_filter<char>     line_filter;
typedef basic_line_filter<wchar_t>  wline_filter;

} } // End namespace boost::io

Template parameters

Ch	-	The character type
Alloc	-	A standard library allocator type ([ISO], 20.1.5), used to allocate a character buffer

`line_filter::do_filter`

    virtual string_type do_filter(const string_type& line) = 0;

The argument line represents a single line of unfiltered text, not including any terminal newline character. Returns the result of filtering line.

Example

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

#include <boost/iostreams/filter/line.hpp>

namespace io = boost::iostreams;

class long_line_counter : public io::line_filter {
public
    explicit long_line_counter(int max_length = 80) 
        : max_(max_length), count_(0) 
        { }
    int count() const { return count_; }
private:
    std::string do_filter(const std::string& line)
    {
        if (line.size() > max_)
            ++count_;
    }
    int max_;
    int count_;
};

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

Class Template basic_line_filter