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