std::regex_iterator is a read-only iterator that accesses the individual matches of a regular expression within the underlying character sequence. It meets the requirements of aLegacyForwardIterator, except that for dereferenceable valuesa andb witha== b,*a and*b will not be bound to the same object.

On construction, and on every increment, it callsstd::regex_search and remembers the result (that is, saves a copy of thestd::match_results<BidirIt> value). The first object may be read when the iterator is constructed or when the first dereferencing is done. Otherwise, dereferencing only returns a copy of the most recently obtained regex match.

The default-constructedstd::regex_iterator is the end-of-sequence iterator. When a validstd::regex_iterator is incremented after reaching the last match (std::regex_search returnsfalse), it becomes equal to the end-of-sequence iterator. Dereferencing or incrementing it further invokes undefined behavior.

A typical implementation ofstd::regex_iterator holds the begin and the end iterators for the underlying sequence (two instances ofBidirIt), a pointer to the regular expression (const regex_type*), the match flags (std::regex_constants::match_flag_type), and the current match (std::match_results<BidirIt>).

[edit]Type requirements

[edit]Specializations

Several specializations for common character sequence types are defined:

[edit]Member types

[edit]Data members

[edit]Member functions

[edit]Notes

It is the programmer's responsibility to ensure that thestd::basic_regex object passed to the iterator's constructor outlives the iterator. Because the iterator stores a pointer to the regex, incrementing the iterator after the regex was destroyed accesses a dangling pointer.

If the part of the regular expression that matched is just anassertion (^,$,\b,\B), the match stored in the iterator is a zero-length match, that is,match[0].first== match[0].second.

[edit]Example

#include <iostream>#include <iterator>#include <regex>#include <string> int main(){conststd::string s="Quick brown fox."; std::regex words_regex("[^\\s]+");auto words_begin= std::sregex_iterator(s.begin(), s.end(), words_regex);auto words_end= std::sregex_iterator(); std::cout<<"Found "<<std::distance(words_begin, words_end)<<" words:\n"; for(std::sregex_iterator i= words_begin; i!= words_end;++i){std::smatch match=*i;std::string match_str= match.str();std::cout<< match_str<<'\n';}}

Found 3 words:Quickbrownfox.

[edit]Defect reports

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

1. ↑iterator_category was unchanged by the resolution, because changing it tostd::input_iterator_tag might break too much existing code.

[edit]See also

• In other languages

• Deutsch
• Español
• Français
• Italiano
• 日本語
• Português
• Русский
• 中文