Regular expressions library
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) | 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) |
[edit]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) |
[edit]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) |
[edit]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) |
[edit]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) |
[edit]Constants
Defined in namespace std::regex_constants | |
(C++11) | general options controlling regex behavior (typedef) |
(C++11) | options specific to matching (typedef) |
(C++11) | 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("(\\w+)");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"; constint 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 20 words Words longer than 6 characters: 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].
