std::regex_token_iterator
Defined in header <regex>
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template< class BidirIt, |
(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 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.
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Specializations
Several specializations for common character sequence types are defined:
Defined in header
<regex> | |
Type | Definition |
cregex_token_iterator
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regex_token_iterator<const char*> |
wcregex_token_iterator
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regex_token_iterator<const wchar_t*> |
sregex_token_iterator
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regex_token_iterator<std::string::const_iterator> |
wsregex_token_iterator
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regex_token_iterator<std::wstring::const_iterator> |
Member types
Member type | Definition |
value_type
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std::sub_match<BidirIt> |
difference_type
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std::ptrdiff_t |
pointer
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const value_type* |
reference
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const value_type& |
iterator_category
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std::forward_iterator_tag |
regex_type
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basic_regex<CharT, Traits> |
Member functions
constructs a new regex_token_iterator (public member function) | |
(destructor) (implicitly declared) |
destructs a regex_token_iterator , including the cached value (public member function) |
assigns contents (public member function) | |
compares two regex_token_iterator s (public member function) | |
accesses current submatch (public member function) | |
advances the iterator to the next submatch (public member function) |
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.
Example
#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::sregex_token_iterator(), std::ostream_iterator<std::string>(std::cout, "\n")); // iterating the first submatches std::string html = "<p><a href=\"http://google.com\">google</a> " "< a HREF =\"http://apiref.com\">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::sregex_token_iterator(), std::ostream_iterator<std::string>(std::cout, "\n")); }
Output:
Quick brown fox. http://google.com http://apiref.com