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).
Several specializations for common character sequence types are defined:
Type Definitionstd::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 [edit] Member functions [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::sregex_token_iterator(),
std::ostream_iterator<std::string>(std::cout, "\n"));
std::cout << '\n';
// Iterating the first submatches
const std::string html = R"(<p><a href="http://google.com">google</a> )"
R"(< a HREF ="http://cppreference.com">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::sregex_token_iterator(),
std::ostream_iterator<std::string>(std::cout, "\n"));
}
Output:
Quick brown fox. http://google.com http://cppreference.com[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
iterator_category was unchanged by the resolution, because changing it to std::input_iterator_tag might break too much existing code.RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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