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- [/
- / 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 Matching and Searching]
- [h2 Overview]
- Once you have created a regex object, you can use the _regex_match_ and _regex_search_ algorithms to find patterns
- in strings. This page covers the basics of regex matching and searching. In all cases, if you are familiar with
- how _regex_match_ and _regex_search_ in the _regexpp_ library work, xpressive's versions work the same way.
- [h2 Seeing if a String Matches a Regex]
- The _regex_match_ algorithm checks to see if a regex matches a given input.
- [warning The _regex_match_ algorithm will only report success if the regex matches the ['whole input],
- from beginning to end. If the regex matches only a part of the input, _regex_match_ will return false. If you
- want to search through the string looking for sub-strings that the regex matches, use the _regex_search_
- algorithm.]
- The input can be a bidirectional range such as `std::string`, a C-style null-terminated string or a pair of
- iterators. In all cases, the type of the iterator used to traverse the input sequence must match the iterator
- type used to declare the regex object. (You can use the table in the
- [link boost_xpressive.user_s_guide.quick_start.know_your_iterator_type Quick Start] to find the correct regex
- type for your iterator.)
- cregex cre = +_w; // this regex can match C-style strings
- sregex sre = +_w; // this regex can match std::strings
- if( regex_match( "hello", cre ) ) // OK
- { /*...*/ }
- if( regex_match( std::string("hello"), sre ) ) // OK
- { /*...*/ }
- if( regex_match( "hello", sre ) ) // ERROR! iterator mis-match!
- { /*...*/ }
- The _regex_match_ algorithm optionally accepts a _match_results_ struct as an out parameter. If given, the _regex_match_
- algorithm fills in the _match_results_ struct with information about which parts of the regex matched which
- parts of the input.
- cmatch what;
- cregex cre = +(s1= _w);
- // store the results of the regex_match in "what"
- if( regex_match( "hello", what, cre ) )
- {
- std::cout << what[1] << '\n'; // prints "o"
- }
- The _regex_match_ algorithm also optionally accepts a _match_flag_type_ bitmask. With _match_flag_type_, you can
- control certain aspects of how the match is evaluated. See the _match_flag_type_ reference for a complete list
- of the flags and their meanings.
- std::string str("hello");
- sregex sre = bol >> +_w;
- // match_not_bol means that "bol" should not match at [begin,begin)
- if( regex_match( str.begin(), str.end(), sre, regex_constants::match_not_bol ) )
- {
- // should never get here!!!
- }
- Click [link boost_xpressive.user_s_guide.examples.see_if_a_whole_string_matches_a_regex here] to see a complete
- example program that shows how to use _regex_match_. And check the _regex_match_ reference to see a complete list
- of the available overloads.
- [h2 Searching for Matching Sub-Strings]
- Use _regex_search_ when you want to know if an input sequence contains a sub-sequence that a regex matches.
- _regex_search_ will try to match the regex at the beginning of the input sequence and scan forward in the
- sequence until it either finds a match or exhausts the sequence.
- In all other regards, _regex_search_ behaves like _regex_match_ ['(see above)]. In particular, it can operate
- on a bidirectional range such as `std::string`, C-style null-terminated strings or iterator ranges. The same
- care must be taken to ensure that the iterator type of your regex matches the iterator type of your input
- sequence. As with _regex_match_, you can optionally provide a _match_results_ struct to receive the results
- of the search, and a _match_flag_type_ bitmask to control how the match is evaluated.
- Click [link boost_xpressive.user_s_guide.examples.see_if_a_string_contains_a_sub_string_that_matches_a_regex here]
- to see a complete example program that shows how to use _regex_search_. And check the _regex_search_ reference to
- see a complete list of the available overloads.
- [endsect]
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