https://en.cppreference.com/w/cpp/regex

The regular expressions library provides a class that represents Regular expression | 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

  .

• Pattern. This is the regular expression itself. It determines what constitutes a match. It is an object of type

  , constructed from a string with special syntax. See

  for the description of supported syntax variations.

• Matched array. The information about matches may be retrieved as an object of type

  .

• Replacement string. This is a string that determines how to replace the matches, see

  for the description of supported syntax variations.

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

These functions are used to apply the regular expression encapsulated in a regex to a target sequence of characters.

The regex iterators are used to traverse the entire set of regular expression matches found within a sequence.

This class defines the type of objects thrown as exceptions to report errors from the regular expressions library.

The regex traits class is used to encapsulate the localizable aspects of a regex.

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";

   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 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]. }}