[/
/ Copyright (c) 2008 Eric Niebler
/
/ 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)
/]
[section Examples]
Below you can find six complete sample programs.
\n
----
[h4 See if a whole string matches a regex]
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:
[pre
hello world!
hello
world
]
\n
[link boost_xpressive.user_s_guide.examples top]
----
[h4 See if a string contains a sub-string that matches a regex]
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:
[pre
5/30/1973
30
5
1973
/
]
\n
[link boost_xpressive.user_s_guide.examples top]
----
[h4 Replace all sub-strings that match a regex]
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:
[pre
I was born on <date>5/30/1973</date> at 7am.
]
\n
[link boost_xpressive.user_s_guide.examples top]
----
[h4 Find all the sub-strings that match a regex and step through them one at a time]
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:
[pre
This
is
his
face
]
\n
[link boost_xpressive.user_s_guide.examples top]
----
[h4 Split a string into tokens that each match a regex]
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:
[pre
4
40
3
35
2
32
]
\n
[link boost_xpressive.user_s_guide.examples top]
----
[h4 Split a string using a regex as a delimiter]
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 _regex_token_iterator_
that returns the parts of the string that do ['not] match the regex.
#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:
[pre
{Now }{is the time }{for all good men}{ to come to the aid of their}{ country.}
]
\n
[link boost_xpressive.user_s_guide.examples top]
----
[h4 Display a tree of nested results]
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 ) );
}
};
[link boost_xpressive.user_s_guide.examples top]
[endsect]
