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### regex_token_iterator

The template class `regex_token_iterator` is an iterator adapter; that is to say it represents a new view of an existing iterator sequence, by enumerating all the occurrences of a regular expression within that sequence, and presenting one or more character sequence for each match found. Each position enumerated by the iterator is a `sub_match` object that represents what matched a particular sub-expression within the regular expression. When class `regex_token_iterator` is used to enumerate a single sub-expression with index -1, then the iterator performs field splitting: that is to say it enumerates one character sequence for each section of the character container sequence that does not match the regular expression specified.

    template <class BidirectionalIterator,
             class charT = iterator_traits<BidirectionalIterator>::value_type,
             class traits = regex_traits<charT> >
    class regex_token_iterator
    {
    public:
       typedef          basic_regex<charT, traits>                              regex_type;
       typedef          sub_match<BidirectionalIterator>                        value_type;
       typedef typename iterator_traits<BidirectionalIterator>::difference_type difference_type;
       typedef          const value_type*                                       pointer;
       typedef          const value_type&                                       reference;
       typedef          std::forward_iterator_tag                               iterator_category;

       regex_token_iterator();
       regex_token_iterator(BidirectionalIterator a,
                            BidirectionalIterator b,
                            const regex_type& re,
                            int submatch = 0,
                            match_flag_type m = match_default);
       regex_token_iterator(BidirectionalIterator a,
                            BidirectionalIterator b,
                            const regex_type& re,
                            const std::vector<int>& submatches,
                            match_flag_type m = match_default);
       template <std::size_t N>
       regex_token_iterator(BidirectionalIterator a,
                            BidirectionalIterator b,
                            const regex_type& re,
                            const int (&submatches)[N],
                            match_flag_type m = match_default);
       regex_token_iterator(const regex_token_iterator&);
       regex_token_iterator& operator=(const regex_token_iterator&);
       bool operator==(const regex_token_iterator&)const;
       bool operator!=(const regex_token_iterator&)const;
       const value_type& operator*()const;
       const value_type* operator->()const;
       regex_token_iterator& operator++();
       regex_token_iterator operator++(int);
    };

    typedef regex_token_iterator<const char*>                   cregex_token_iterator;
    typedef regex_token_iterator<std::string::const_iterator>   sregex_token_iterator;
    #ifndef BOOST_NO_WREGEX
    typedef regex_token_iterator<const wchar_t*>                wcregex_token_iterator;
    typedef regex_token_iterator<<std::wstring::const_iterator> wsregex_token_iterator;
    #endif

    template <class charT, class traits>
    regex_token_iterator<const charT*, charT, traits>
       make_regex_token_iterator(
             const charT* p,
             const basic_regex<charT, traits>& e,
             int submatch = 0,
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, class ST, class SA>
    regex_token_iterator<typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
       make_regex_token_iterator(
             const std::basic_string<charT, ST, SA>& p,
             const basic_regex<charT, traits>& e,
             int submatch = 0,
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, std::size_t N>
    regex_token_iterator<const charT*, charT, traits>
    make_regex_token_iterator(
             const charT* p,
             const basic_regex<charT, traits>& e,
             const int (&submatch)[N],
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, class ST, class SA, std::size_t N>
    regex_token_iterator<typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
       make_regex_token_iterator(
             const std::basic_string<charT, ST, SA>& p,
             const basic_regex<charT, traits>& e,
             const int (&submatch)[N],
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits>
    regex_token_iterator<const charT*, charT, traits>
       make_regex_token_iterator(
             const charT* p,
             const basic_regex<charT, traits>& e,
             const std::vector<int>& submatch,
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, class ST, class SA>
    regex_token_iterator<
          typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
       make_regex_token_iterator(
             const std::basic_string<charT, ST, SA>& p,
             const basic_regex<charT, traits>& e,
             const std::vector<int>& submatch,
             regex_constants::match_flag_type m = regex_constants::match_default);

##### Description

    regex_token_iterator();

Effects: constructs an end of sequence iterator.

    regex_token_iterator(BidirectionalIterator a,
                         BidirectionalIterator b,
                         const regex_type& re,
                         int submatch = 0,
                         match_flag_type m = match_default);

Preconditions: `!re.empty()`. Object re shall exist for the lifetime of the iterator constructed from it.

Effects: constructs a `regex_token_iterator` that will enumerate one string for each regular expression match of the expression re found within the sequence [a,b), using match flags m (see `match_flag_type`). The string enumerated is the sub-expression submatch for each match found; if submatch is -1, then enumerates all the text sequences that did not match the expression re (that is to performs field splitting).

Throws: `std::runtime_error` if the complexity of matching the expression against an N character string begins to exceed O(N2), or if the program runs out of stack space while matching the expression (if Boost.Regex is configured in recursive mode), or if the matcher exhausts its permitted memory allocation (if Boost.Regex is configured in non-recursive mode).

    regex_token_iterator(BidirectionalIterator a,
                         BidirectionalIterator b,
                         const regex_type& re,
                         const std::vector<int>& submatches,
                         match_flag_type m = match_default);

Preconditions: `submatches.size() && !re.empty()`. Object re shall exist for the lifetime of the iterator constructed from it.

Effects: constructs a `regex_token_iterator` that will enumerate `submatches.size()` strings for each regular expression match of the expression re found within the sequence [a,b), using match flags m (see `match_flag_type`). For each match found one string will be enumerated for each sub-expression index contained within submatches vector; if `submatches[0]` is -1, then the first string enumerated for each match will be all of the text from end of the last match to the start of the current match, in addition there will be one extra string enumerated when no more matches can be found: from the end of the last match found, to the end of the underlying sequence.

Throws: `std::runtime_error` if the complexity of matching the expression against an N character string begins to exceed O(N2), or if the program runs out of stack space while matching the expression (if Boost.Regex is configured in recursive mode), or if the matcher exhausts its permitted memory allocation (if Boost.Regex is configured in non-recursive mode).

    template <std::size_t N>
    regex_token_iterator(BidirectionalIterator a,
                         BidirectionalIterator b,
                         const regex_type& re,
                         const int (&submatches)[R],
                         match_flag_type m = match_default);

Preconditions: `!re.empty()`. Object re shall exist for the lifetime of the iterator constructed from it.

Effects: constructs a `regex_token_iterator` that will enumerate R strings for each regular expression match of the expression re found within the sequence [a,b), using match flags m (see `match_flag_type`). For each match found one string will be enumerated for each sub-expression index contained within the submatches array; if `submatches[0]` is -1, then the first string enumerated for each match will be all of the text from end of the last match to the start of the current match, in addition there will be one extra string enumerated when no more matches can be found: from the end of the last match found, to the end of the underlying sequence.

Throws: `std::runtime_error` if the complexity of matching the expression against an N character string begins to exceed O(N2), or if the program runs out of stack space while matching the expression (if Boost.Regex is configured in recursive mode), or if the matcher exhausts its permitted memory allocation (if Boost.Regex is configured in non-recursive mode).

    regex_token_iterator(const regex_token_iterator& that);

Effects: constructs a copy of `that`.

Postconditions: `*this == that`.

    regex_token_iterator& operator=(const regex_token_iterator& that);

Effects: sets `*this` to be equal to `that`.

Postconditions: `*this == that`.

    bool operator==(const regex_token_iterator&)const;

Effects: returns true if `*this` is the same position as `that`.

    bool operator!=(const regex_token_iterator&)const;

Effects: returns `!(*this == that)`.

    const value_type& operator*()const;

Effects: returns the current character sequence being enumerated.

    const value_type* operator->()const;

Effects: returns `&(*this)`.

    regex_token_iterator& operator++();

Effects: Moves on to the next character sequence to be enumerated.

Throws: `std::runtime_error` if the complexity of matching the expression against an N character string begins to exceed O(N2), or if the program runs out of stack space while matching the expression (if Boost.Regex is configured in recursive mode), or if the matcher exhausts its permitted memory allocation (if Boost.Regex is configured in non-recursive mode).

Returns: `*this`.

    regex_token_iterator& operator++(int);

Effects: constructs a copy result of `*this`, then calls `++(*this)`.

Returns: result.

    template <class charT, class traits>
    regex_token_iterator<const charT*, charT, traits>
       make_regex_token_iterator(
             const charT* p,
             const basic_regex<charT, traits>& e,
             int submatch = 0,
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, class ST, class SA>
    regex_token_iterator<typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
       make_regex_token_iterator(
             const std::basic_string<charT, ST, SA>& p,
             const basic_regex<charT, traits>& e,
             int submatch = 0,
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, std::size_t N>
    regex_token_iterator<const charT*, charT, traits>
    make_regex_token_iterator(
             const charT* p,
             const basic_regex<charT, traits>& e,
             const int (&submatch)[N],
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, class ST, class SA, std::size_t N>
    regex_token_iterator<
          typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
       make_regex_token_iterator(
             const std::basic_string<charT, ST, SA>& p,
             const basic_regex<charT, traits>& e,
             const int (&submatch)[N],
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits>
    regex_token_iterator<const charT*, charT, traits>
       make_regex_token_iterator(
             const charT* p,
             const basic_regex<charT, traits>& e,
             const std::vector<int>& submatch,
             regex_constants::match_flag_type m = regex_constants::match_default);

    template <class charT, class traits, class ST, class SA>
    regex_token_iterator<
          typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
       make_regex_token_iterator(
             const std::basic_string<charT, ST, SA>& p,
             const basic_regex<charT, traits>& e,
             const std::vector<int>& submatch,
             regex_constants::match_flag_type m = regex_constants::match_default);

Effects: returns a `regex_token_iterator` that enumerates one `sub_match` for each value in submatch for each occurrence of regular expression e in string p, matched using `match_flag_type` m.

##### Examples

The following example takes a string and splits it into a series of tokens:

    #include <iostream>
    #include <boost/regex.hpp>

    using namespace std;

    int main(int argc)
    {
       string s;
       do{
          if(argc == 1)
          {
             cout << "Enter text to split (or \"quit\" to exit): ";
             getline(cin, s);
             if(s == "quit") break;
          }
          else
             s = "This is a string of tokens";

          boost::regex re("\\s+");
          boost::sregex_token_iterator i(s.begin(), s.end(), re, -1);
          boost::sregex_token_iterator j;

          unsigned count = 0;
          while(i != j)
          {
             cout << *i++ << endl;
             count++;
          }
          cout << "There were " << count << " tokens found." << endl;

       }while(argc == 1);
       return 0;
    }

The following example takes a html file and outputs a list of all the linked files:

    #include <fstream>
    #include <iostream>
    #include <iterator>
    #include <boost/regex.hpp>

    boost::regex e("<\\s*A\\s+[^>]*href\\s*=\\s*\"([^\"]*)\"",
                   boost::regex::normal | boost::regbase::icase);

    void load_file(std::string& s, std::istream& is)
    {
       s.erase();
       //
       // attempt to grow string buffer to match file size,
       // this doesn't always work...
       s.reserve(is.rdbuf()->in_avail());
       char c;
       while(is.get(c))
       {
          // use logarithmic growth stategy, in case
          // in_avail (above) returned zero:
          if(s.capacity() == s.size())
             s.reserve(s.capacity() * 3);
          s.append(1, c);
       }
    }

    int main(int argc, char** argv)
    {
       std::string s;
       int i;
       for(i = 1; i < argc; ++i)
       {
          std::cout << "Findings URL's in " << argv[i] << ":" << std::endl;
          s.erase();
          std::ifstream is(argv[i]);
          load_file(s, is);
          boost::sregex_token_iterator i(s.begin(), s.end(), e, 1);
          boost::sregex_token_iterator j;
          while(i != j)
          {
             std::cout << *i++ << std::endl;
          }
       }
       //
       // alternative method:
       // test the array-literal constructor, and split out the whole
       // match as well as $1....
       //
       for(i = 1; i < argc; ++i)
       {
          std::cout << "Findings URL's in " << argv[i] << ":" << std::endl;
          s.erase();
          std::ifstream is(argv[i]);
          load_file(s, is);
          const int subs[] = {1, 0,};
          boost::sregex_token_iterator i(s.begin(), s.end(), e, subs);
          boost::sregex_token_iterator j;
          while(i != j)
          {
             std::cout << *i++ << std::endl;
          }
       }

       return 0;
    }