Regular expressions library
Defined in header
<regex> |
The regular expressions library provides a class that represents regular expressions, which are a kind of mini-language used to perform pattern matching within strings. Almost all operations with regexes can be characterized by operating on several of the following objects:
- Target sequence. The character sequence that is searched for a pattern. This may be a range specified by two iterators, a null-terminated character string or a std::string.
- Pattern. This is the regular expression itself. It determines what constitutes a match. It is an object of type std::basic_regex, constructed from a string with special syntax. See syntax_option_type for the description of supported syntax variations.
- Matched array. The information about matches may be retrieved as an object of type std::match_results.
- Replacement string. This is a string that determines how to replace the matches, see match_flag_type for the description of supported syntax variations.
Contents |
[edit] Main classes
These classes encapsulate a regular expression and the results of matching a regular expression within a target sequence of characters.
(C++11)
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regular expression object (class template) |
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identifies the sequence of characters matched by a sub-expression (class template) |
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identifies one regular expression match, including all sub-expression matches (class template) |
[edit] Algorithms
These functions are used to apply the regular expression encapsulated in a regex to a target sequence of characters.
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attempts to match a regular expression to an entire character sequence (function template) |
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attempts to match a regular expression to any part of a character sequence (function template) |
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replaces occurrences of a regular expression with formatted replacement text (function template) |
[edit] Iterators
The regex iterators are used to traverse the entire set of regular expression matches found within a sequence.
(C++11)
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iterates through all regex matches within a character sequence (class template) |
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iterates through the specified sub-expressions within all regex matches in a given string or through unmatched substrings (class template) |
[edit] Exceptions
This class defines the type of objects thrown as exceptions to report errors from the regular expressions library.
(C++11)
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reports errors generated by the regular expressions library (class) |
[edit] Traits
The regex traits class is used to encapsulate the localizable aspects of a regex.
(C++11)
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provides metainformation about a character type, required by the regex library (class template) |
[edit] Constants
Defined in namespace
std::regex_constants |
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(C++11)
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general options controlling regex behavior (typedef) |
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options specific to matching (typedef) |
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describes different types of matching errors (typedef) |
[edit] Example
#include <iostream> #include <iterator> #include <string> #include <regex> int main() { std::string s = "Some people, when confronted with a problem, think " "\"I know, I'll use regular expressions.\" " "Now they have two problems."; std::regex self_regex("REGULAR EXPRESSIONS", std::regex_constants::ECMAScript | std::regex_constants::icase); if (std::regex_search(s, self_regex)) { std::cout << "Text contains the phrase 'regular expressions'\n"; } std::regex word_regex("(\\S+)"); auto words_begin = std::sregex_iterator(s.begin(), s.end(), word_regex); auto words_end = std::sregex_iterator(); std::cout << "Found " << std::distance(words_begin, words_end) << " words\n"; const int N = 6; std::cout << "Words longer than " << N << " characters:\n"; for (std::sregex_iterator i = words_begin; i != words_end; ++i) { std::smatch match = *i; std::string match_str = match.str(); if (match_str.size() > N) { std::cout << " " << match_str << '\n'; } } std::regex long_word_regex("(\\w{7,})"); std::string new_s = std::regex_replace(s, long_word_regex, "[$&]"); std::cout << new_s << '\n'; }
Output:
Text contains the phrase 'regular expressions' Found 19 words Words longer than 6 characters: people, confronted problem, regular expressions." problems. Some people, when [confronted] with a [problem], think "I know, I'll use [regular] [expressions]." Now they have two [problems].