Regular expressions library

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Regular expressions library

Classes

basic_regex (C++11)

sub_match (C++11)

match_results (C++11)

Algorithms

regex_match (C++11)

regex_search (C++11)

regex_replace (C++11)

Iterators

regex_iterator (C++11)

regex_token_iterator (C++11)

Exceptions

regex_error (C++11)

Traits

regex_traits (C++11)

Constants

syntax_option_type (C++11)

match_flag_type (C++11)

error_type (C++11)

Regex Grammar

Modified ECMAScript-262 (C++11)

 

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.

Also provided in the regular expressions library are utility classes that provide support for various algorithms, iterators, exceptions, and type traits.

Main classes

These classes encapsulate a regular expression and the results of matching a regular expression within a target sequence of characters.

basic_regex (C++11)	regular expression object (class template)
sub_match (C++11)	identifies the sequence of characters matched by a sub-expression (class template)
match_results (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.

regex_match (C++11)	attempts to match a regular expression to an entire character sequence (function template)
regex_search (C++11)	attempts to match a regular expression to any part of a character sequence (function template)
regex_replace (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.

regex_iterator (C++11)	iterates through all regex matches within a character sequence (class template)
regex_token_iterator (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.

regex_error (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.

regex_traits (C++11)

provides metainformation about a character type, required by the regex library (class template)

Constants

Defined in namespace std::regex_constants
syntax_option_type (C++11)	general options controlling regex behavior (typedef)
match_flag_type (C++11)	options specific to matching (typedef)
error_type (C++11)	describes different types of matching errors (typedef)

Example

Run this code

#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 greater 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 greater 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].