Class Template `basic_grep_filter`

Description
Headers
Installation
Reference

Description

The class template basic_grep_filter filters a character sequence line by line using a regular expression provided at construction, in a manner similar to the command-line utility grep ([IEEE]). The filter uses regular expressions from the Boost Regular Expression Library ([Maddock]).

By default, the filtered character sequence consists of those lines of the unfiltered sequence that contain a subsequence matching the regular expression. By specifying appropriate options at construction, basic_grep_filter can be made to pass through only those lines which exactly match the regular expression (as if the option -x had been passed to the command-line utility) or only those lines that do not contain a match (as if the option -v had been passed to the command-line utility).

A running count of the lines in the filtered character sequence is available via the member function count.

Headers

<boost/iostreams/filter/grep.hpp>

Installation

The template basic_grep_filter uses the Boost Regular Expression Library, which must be built separately. See here for details.

Reference

Synopsis

namespace boost { namespace iostreams {

#include <boost/function.hpp>
#include <boost/regex.hpp>

namespace grep {

const int invert;
const int whole_line;

}

template< typename Ch,
          typename Tr = regex_traits<Ch>,
          typename Alloc = std::allocator<Ch> >
class basic_grep_filter {   
public:
    basic_grep_filter( const basic_regex<Ch, Tr, Alloc>& pattern,
                       regex_constants::match_flag_type flags = 
                           regex_constants::match_default,
                       int options = 0 );
    int count() const;
};

typedef basic_grep_filter<char>     grep_filter;
typedef basic_grep_filter<wchar_t>  wgrep_filter;

} } // End namespace boost::io

Template parameters

Ch	-	The character type
Tr	-	The regular expression traits type
Alloc	-	A standard library allocator type ([ISO], 20.1.5), used to allocate character buffers

`basic_grep_filter::basic_grep_filter`

    basic_grep_filter( const basic_regex<Ch, Tr, Alloc>& pattern,
                       regex_constants::match_flag_type flags = 
                           regex_constants::match_default,
                       int options = 0 );

Constructs a basic_grep_filter from the given regular expression, match flags, and grep options. The parameters have the following interpretations:

pattern	-	The regular expression to be matched against the stream of unfiltered data
flags	-	The flags passed to regex_search or regex_match to specify regular expression matching behavior
options	-	A bitwise OR of zero or more constants from the namespace `boost::iostreams::grep`. Currently two constants are recongnized: `grep::whole_line` causes the filter to pass through only those lines which exactly match the regular expression, and `grep::invert` causes the filter to pass through only those lines that do not contain a match.

`basic_grep_filter::count`

    int count() const;

Returns a running count of the lines passed through from the unfiltered character sequence to the filtered character sequence. The count is reset to zero automatically when the filter begins processing a new character sequence.

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_grep_filter