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