template< class BidirIt, class CharT = typename std::iterator_traits<BidirIt>::value_type, class Traits = std::regex_traits<CharT> > class regex_iterator | (since C++11) |
std::regex_iterator
is a read-only ForwardIterator
that accesses the individual matches of a regular expression within the underlying character sequence.
On construction, and on every increment, it calls std::regex_search
and remembers the result (that is, saves a copy of the value std::match_results<BidirIt>
). 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-constructed std::regex_iterator
is the end-of-sequence iterator. When a valid std::regex_iterator
is incremented after reaching the last match (std::regex_search
returns false
), it becomes equal to the end-of-sequence iterator. Dereferencing or incrementing it further invokes undefined behavior.
A typical implementation of std::regex_iterator
holds the begin and the end iterators for the underlying sequence (two instances of BidirIt), 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>
).
-BidirIt must meet the requirements of BidirectionalIterator . |
Several specializations for common character sequence types are defined:
Defined in header <regex> |
|
---|---|
Type | Definition |
cregex_iterator | regex_iterator<const char*> |
wcregex_iterator | regex_iterator<const wchar_t*> |
sregex_iterator | regex_iterator<std::string::const_iterator> |
wsregex_iterator | regex_iterator<std::wstring::const_iterator> |
Member type | Definition |
---|---|
value_type | std::match_results<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> |
constructs a new regex_iterator (public member function) |
|
(destructor)
(implicitly declared) | destructs a regex_iterator , including the cached value (public member function) |
assigns contents (public member function) |
|
compares two regex_iterator s (public member function) |
|
accesses the current match (public member function) |
|
advances the iterator to the next match (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 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 an assertion (^
, $
, \b
, \B
), the match stored in the iterator is a zero-length match, that is, match[0].first == match[0].second
.
#include <regex> #include <iterator> #include <iostream> #include <string> int main() { const std::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'; } }
Output:
Found 3 words: Quick brown fox.
(C++11) | identifies one regular expression match, including all sub-expression matches (class template) |
(C++11) | check if a regular expression occurs anywhere within a string (function template) |
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