Defined in header <regex> |
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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
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.
Main classes
These classes encapsulate a regular expression and the results of matching a regular expression within a target sequence of characters.
(C++11) | regular expression object (class template) |
(C++11) | identifies the sequence of characters matched by a sub-expression (class template) |
(C++11) | identifies one regular expression match, including all sub-expression matches (class template) |
Algorithms
These functions are used to apply the regular expression encapsulated in a regex to a target sequence of characters.
(C++11) | attempts to match a regular expression to an entire character sequence (function template) |
(C++11) | attempts to match a regular expression to any part of a character sequence (function template) |
(C++11) | replaces occurrences of a regular expression with formatted replacement text (function template) |
Iterators
The regex iterators are used to traverse the entire set of regular expression matches found within a sequence.
(C++11) | iterates through all regex matches within a character sequence (class template) |
(C++11) | iterates through the specified sub-expressions within all regex matches in a given string or through unmatched substrings (class template) |
Exceptions
This class defines the type of objects thrown as exceptions to report errors from the regular expressions library.
(C++11) | reports errors generated by the regular expressions library (class) |
Traits
The regex traits class is used to encapsulate the localizable aspects of a regex.
(C++11) | provides metainformation about a character type, required by the regex library (class template) |
Constants
Defined in namespace std::regex_constants | |
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(C++11) | general options controlling regex behavior (typedef) |
(C++11) | options specific to matching (typedef) |
(C++11) | describes different types of matching errors (typedef) |
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].
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