std::regex_token_iterator (3) - Linux Man Pages

std::regex_token_iterator: std::regex_token_iterator


std::regex_token_iterator - std::regex_token_iterator


Defined in header <regex>
class BidirIt,
class CharT = typename std::iterator_traits<BidirIt>::value_type, (since C++11)
class Traits = std::regex_traits<CharT>
> class regex_token_iterator

std::regex_token_iterator is a read-only LegacyForwardIterator that accesses the individual sub-matches of every match of a regular expression within the underlying character sequence. It can also be used to access the parts of the sequence that were not matched by the given regular expression (e.g. as a tokenizer).
On construction, it constructs an std::regex_iterator and on every increment it steps through the requested sub-matches from the current match_results, incrementing the underlying regex_iterator when incrementing away from the last submatch.
The default-constructed std::regex_token_iterator is the end-of-sequence iterator. When a valid std::regex_token_iterator is incremented after reaching the last submatch of the last match, it becomes equal to the end-of-sequence iterator. Dereferencing or incrementing it further invokes undefined behavior.
Just before becoming the end-of-sequence iterator, a std::regex_token_iterator may become a suffix iterator, if the index -1 (non-matched fragment) appears in the list of the requested submatch indexes. Such iterator, if dereferenced, returns a match_results corresponding to the sequence of characters between the last match and the end of sequence.
A typical implementation of std::regex_token_iterator holds the underlying std::regex_iterator, a container (e.g. std::vector<int>) of the requested submatch indexes, the internal counter equal to the index of the submatch, a pointer to std::sub_match, pointing at the current submatch of the current match, and a std::match_results object containing the last non-matched character sequence (used in tokenizer mode).

Type requirements

BidirIt must meet the requirements of LegacyBidirectionalIterator.


Several specializations for common character sequence types are defined:

Defined in header <regex>
Type Definition
cregex_token_iterator regex_token_iterator<const char*>
wcregex_token_iterator regex_token_iterator<const wchar_t*>
sregex_token_iterator regex_token_iterator<std::string::const_iterator>
wsregex_token_iterator regex_token_iterator<std::wstring::const_iterator>

Member types

Member type Definition
value_type std::sub_match<BidirIt>
difference_type std::ptrdiff_t
pointer const value_type*
reference const value_type&
iterator_category std::forward_iterator_tag
regex_type basic_regex<CharT, Traits>

Member functions

                      constructs a new regex_token_iterator
constructor (public member function)

destructor destructs a regex_token_iterator, including the cached value
                      (public member function)
(implicitly declared)
                      assigns contents
operator= (public member function)
                      compares two regex_token_iterators
operator== (public member function)
                      accesses current submatch
operator* (public member function)
                      advances the iterator to the next submatch
operator++ (public member function)


It is the programmer's responsibility to ensure that the std::basic_regex object passed to the iterator's constructor outlives the iterator. Because the iterator stores a std::regex_iterator which stores a pointer to the regex, incrementing the iterator after the regex was destroyed results in undefined behavior.


// Run this code

  #include <fstream>
  #include <iostream>
  #include <algorithm>
  #include <iterator>
  #include <regex>

  int main()
     std::string text = "Quick brown fox.";
     // tokenization (non-matched fragments)
     // Note that regex is matched only two times: when the third value is obtained
     // the iterator is a suffix iterator.
     std::regex ws_re("\\s+"); // whitespace
     std::copy( std::sregex_token_iterator(text.begin(), text.end(), ws_re, -1),
                std::ostream_iterator<std::string>(std::cout, "\n"));

     // iterating the first submatches
     std::string html = "<p><a href=\"\">google</a> "
                        "< a HREF =\"\">cppreference</a>\n</p>";
     std::regex url_re("<\\s*A\\s+[^>]*href\\s*=\\s*\"([^\"]*)\"", std::regex::icase);
     std::copy( std::sregex_token_iterator(html.begin(), html.end(), url_re, 1),
                std::ostream_iterator<std::string>(std::cout, "\n"));