308 lines
7.5 KiB
Plaintext
308 lines
7.5 KiB
Plaintext
[/
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/ Copyright (c) 2008 Eric Niebler
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/
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/ Distributed under the Boost Software License, Version 1.0. (See accompanying
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/ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section Examples]
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Below you can find six complete sample programs.
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\n
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----
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[h4 See if a whole string matches a regex]
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This is the example from the Introduction. It is reproduced here for your convenience.
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#include <iostream>
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#include <boost/xpressive/xpressive.hpp>
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using namespace boost::xpressive;
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int main()
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{
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std::string hello( "hello world!" );
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sregex rex = sregex::compile( "(\\w+) (\\w+)!" );
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smatch what;
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if( regex_match( hello, what, rex ) )
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{
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std::cout << what[0] << '\n'; // whole match
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std::cout << what[1] << '\n'; // first capture
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std::cout << what[2] << '\n'; // second capture
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}
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return 0;
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}
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This program outputs the following:
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[pre
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hello world!
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hello
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world
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]
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\n
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[link boost_xpressive.user_s_guide.examples top]
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----
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[h4 See if a string contains a sub-string that matches a regex]
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Notice in this example how we use custom `mark_tag`s to make the pattern more readable.
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We can use the `mark_tag`s later to index into the _match_results_.
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#include <iostream>
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#include <boost/xpressive/xpressive.hpp>
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using namespace boost::xpressive;
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int main()
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{
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char const *str = "I was born on 5/30/1973 at 7am.";
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// define some custom mark_tags with names more meaningful than s1, s2, etc.
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mark_tag day(1), month(2), year(3), delim(4);
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// this regex finds a date
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cregex date = (month= repeat<1,2>(_d)) // find the month ...
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>> (delim= (set= '/','-')) // followed by a delimiter ...
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>> (day= repeat<1,2>(_d)) >> delim // and a day followed by the same delimiter ...
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>> (year= repeat<1,2>(_d >> _d)); // and the year.
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cmatch what;
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if( regex_search( str, what, date ) )
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{
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std::cout << what[0] << '\n'; // whole match
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std::cout << what[day] << '\n'; // the day
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std::cout << what[month] << '\n'; // the month
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std::cout << what[year] << '\n'; // the year
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std::cout << what[delim] << '\n'; // the delimiter
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}
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return 0;
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}
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This program outputs the following:
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[pre
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5/30/1973
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30
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5
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1973
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/
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]
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\n
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[link boost_xpressive.user_s_guide.examples top]
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----
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[h4 Replace all sub-strings that match a regex]
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The following program finds dates in a string and marks them up with pseudo-HTML.
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#include <iostream>
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#include <boost/xpressive/xpressive.hpp>
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using namespace boost::xpressive;
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int main()
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{
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std::string str( "I was born on 5/30/1973 at 7am." );
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// essentially the same regex as in the previous example, but using a dynamic regex
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sregex date = sregex::compile( "(\\d{1,2})([/-])(\\d{1,2})\\2((?:\\d{2}){1,2})" );
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// As in Perl, $& is a reference to the sub-string that matched the regex
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std::string format( "<date>$&</date>" );
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str = regex_replace( str, date, format );
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std::cout << str << '\n';
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return 0;
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}
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This program outputs the following:
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[pre
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I was born on <date>5/30/1973</date> at 7am.
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]
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\n
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[link boost_xpressive.user_s_guide.examples top]
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----
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[h4 Find all the sub-strings that match a regex and step through them one at a time]
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The following program finds the words in a wide-character string.
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It uses `wsregex_iterator`. Notice that dereferencing a `wsregex_iterator`
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yields a `wsmatch` object.
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#include <iostream>
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#include <boost/xpressive/xpressive.hpp>
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using namespace boost::xpressive;
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int main()
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{
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std::wstring str( L"This is his face." );
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// find a whole word
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wsregex token = +alnum;
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wsregex_iterator cur( str.begin(), str.end(), token );
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wsregex_iterator end;
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for( ; cur != end; ++cur )
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{
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wsmatch const &what = *cur;
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std::wcout << what[0] << L'\n';
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}
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return 0;
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}
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This program outputs the following:
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[pre
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This
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is
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his
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face
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]
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\n
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[link boost_xpressive.user_s_guide.examples top]
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----
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[h4 Split a string into tokens that each match a regex]
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The following program finds race times in a string and displays first
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the minutes and then the seconds. It uses _regex_token_iterator_.
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#include <iostream>
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#include <boost/xpressive/xpressive.hpp>
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using namespace boost::xpressive;
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int main()
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{
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std::string str( "Eric: 4:40, Karl: 3:35, Francesca: 2:32" );
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// find a race time
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sregex time = sregex::compile( "(\\d):(\\d\\d)" );
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// for each match, the token iterator should first take the value of
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// the first marked sub-expression followed by the value of the second
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// marked sub-expression
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int const subs[] = { 1, 2 };
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sregex_token_iterator cur( str.begin(), str.end(), time, subs );
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sregex_token_iterator end;
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for( ; cur != end; ++cur )
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{
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std::cout << *cur << '\n';
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}
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return 0;
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}
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This program outputs the following:
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[pre
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4
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40
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3
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35
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2
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32
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]
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\n
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[link boost_xpressive.user_s_guide.examples top]
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----
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[h4 Split a string using a regex as a delimiter]
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The following program takes some text that has been marked up with html and strips
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out the mark-up. It uses a regex that matches an HTML tag and a _regex_token_iterator_
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that returns the parts of the string that do ['not] match the regex.
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#include <iostream>
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#include <boost/xpressive/xpressive.hpp>
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using namespace boost::xpressive;
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int main()
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{
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std::string str( "Now <bold>is the time <i>for all good men</i> to come to the aid of their</bold> country." );
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// find a HTML tag
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sregex html = '<' >> optional('/') >> +_w >> '>';
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// the -1 below directs the token iterator to display the parts of
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// the string that did NOT match the regular expression.
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sregex_token_iterator cur( str.begin(), str.end(), html, -1 );
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sregex_token_iterator end;
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for( ; cur != end; ++cur )
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{
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std::cout << '{' << *cur << '}';
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}
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std::cout << '\n';
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return 0;
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}
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This program outputs the following:
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[pre
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{Now }{is the time }{for all good men}{ to come to the aid of their}{ country.}
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]
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\n
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[link boost_xpressive.user_s_guide.examples top]
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----
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[h4 Display a tree of nested results]
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Here is a helper class to demonstrate how you might display a tree of nested results:
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// Displays nested results to std::cout with indenting
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struct output_nested_results
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{
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int tabs_;
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output_nested_results( int tabs = 0 )
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: tabs_( tabs )
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{
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}
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template< typename BidiIterT >
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void operator ()( match_results< BidiIterT > const &what ) const
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{
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// first, do some indenting
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typedef typename std::iterator_traits< BidiIterT >::value_type char_type;
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char_type space_ch = char_type(' ');
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std::fill_n( std::ostream_iterator<char_type>( std::cout ), tabs_ * 4, space_ch );
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// output the match
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std::cout << what[0] << '\n';
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// output any nested matches
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std::for_each(
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what.nested_results().begin(),
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what.nested_results().end(),
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output_nested_results( tabs_ + 1 ) );
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}
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};
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[link boost_xpressive.user_s_guide.examples top]
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[endsect]
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