< cpp‎ | regex
Defined in header <regex>

    class BidirIt,
    class CharT = typename std::iterator_traits<BidirIt>::value_type,
    class Traits = std::regex_traits<CharT>

> class regex_token_iterator
(since C++11)

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 std::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 indices. 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 indices, 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).


[edit] Type requirements

BidirIt must meet the requirements of LegacyBidirectionalIterator.

[edit] Specializations

Several specializations for common character sequence types are defined:

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

[edit] 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
iterator_concept (C++20) std::input_iterator_tag
regex_type std::basic_regex<CharT, Traits>

[edit] Member functions

constructs a new regex_token_iterator
(public member function) [edit]
(implicitly declared)
destructs a regex_token_iterator, including the cached value
(public member function) [edit]
assigns contents
(public member function) [edit]
(removed in C++20)
compares two regex_token_iterators
(public member function) [edit]
accesses current submatch
(public member function) [edit]
advances the iterator to the next submatch
(public member function) [edit]

[edit] Notes

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.

[edit] Example

#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <regex>
int main()
    // Tokenization (non-matched fragments)
    // Note that regex is matched only two times; when the third value is obtained
    // the iterator is a suffix iterator.
    const std::string text = "Quick brown fox.";
    const 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"));
    std::cout << '\n';
    // Iterating the first submatches
    const std::string html = R"(<p><a href="">google</a> )"
                             R"(< a HREF ="">cppreference</a>\n</p>)";
    const std::regex url_re(R"!!(<\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"));



[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3698
C++20 regex_token_iterator was a forward_iterator
while being a stashing iterator
made input_iterator[1]
  1. iterator_category was unchanged by the resolution, because changing it to std::input_iterator_tag might break too much existing code.