The iterator type regex_iterator will enumerate all of the regular expression matches found in some sequence: dereferencing a regex_iterator yields a reference to a match_results object.

template <class BidirectionalIterator,
         class charT = iterator_traits<BidirectionalIterator>::value_type,
         class traits = regex_traits<charT> >
class regex_iterator
{
public:
   typedef          basic_regex<charT, traits>                              regex_type;
   typedef          match_results<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_iterator();
   regex_iterator(BidirectionalIterator a, BidirectionalIterator b,
                  const regex_type& re,
                  match_flag_type m = match_default);
   regex_iterator(const regex_iterator&);
   regex_iterator& operator=(const regex_iterator&);
   bool operator==(const regex_iterator&)const;
   bool operator!=(const regex_iterator&)const;
   const value_type& operator*()const;
   const value_type* operator->()const;
   regex_iterator& operator++();
   regex_iterator operator++(int);
};

typedef regex_iterator<const char*>                  cregex_iterator;
typedef regex_iterator<std::string::const_iterator>  sregex_iterator;

#ifndef  BOOST_NO_WREGEX
typedef regex_iterator<const wchar_t*>               wcregex_iterator;
typedef regex_iterator<std::wstring::const_iterator> wsregex_iterator;
#endif

template <class charT, class traits> regex_iterator<const charT*, charT, traits>
   make_regex_iterator(const charT* p, const basic_regex<charT, traits>& e,
                       regex_constants::match_flag_type m = regex_constants::match_default);

template <class charT, class traits, class ST, class SA>
   regex_iterator<typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
      make_regex_iterator(const std::basic_string<charT, ST, SA>& p,
                          const basic_regex<charT, traits>& e,
                          regex_constants::match_flag_type m = regex_constants::match_default);

Description

A regex_iterator is constructed from a pair of iterators, and enumerates all occurrences of a regular expression within that iterator range.

regex_iterator();

Effects: constructs an end of sequence regex_iterator.

regex_iterator(BidirectionalIterator a, BidirectionalIterator b,
               const regex_type& re,
               match_flag_type m = match_default);

Effects: constructs a regex_iterator that will enumerate all occurrences of the expression re, within the sequence [a,b), and found using match_flag_type m. The object re must exist for the lifetime of the regex_iterator.

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_iterator(const regex_iterator& that);

Effects: constructs a copy of that.

Postconditions: *this == that.

regex_iterator& operator=(const regex_iterator&);

Effects: sets *this equal to those in that.

Postconditions: *this == that.

bool operator==(const regex_iterator& that)const;

Effects: returns true if *this is equal to that.

bool operator!=(const regex_iterator&)const;

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

const value_type& operator*()const;

Effects: dereferencing a regex_iterator object it yields a const reference to a match_results object, whose members are set as follows:

const value_type* operator->()const;

Effects: returns &(*this).

regex_iterator& operator++();

Effects: moves the iterator to the next match in the underlying sequence, or the end of sequence iterator if none if found. When the last match found matched a zero length string, then the regex_iterator will find the next match as follows: if there exists a non-zero length match that starts at the same location as the last one, then returns it, otherwise starts looking for the next (possibly zero length) match from one position to the right of the last match.

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_iterator operator++(int);

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

Returns: result.

template <class charT, class traits>
regex_iterator<const charT*, charT, traits>
   make_regex_iterator(const charT* p, const basic_regex<charT, traits>& e,
                     regex_constants::match_flag_type m = regex_constants::match_default);

template <class charT, class traits, class ST, class SA>
regex_iterator<typename std::basic_string<charT, ST, SA>::const_iterator, charT, traits>
   make_regex_iterator(const std::basic_string<charT, ST, SA>& p,
                     const basic_regex<charT, traits>& e,
                     regex_constants::match_flag_type m = regex_constants::match_default);

Effects: returns an iterator that enumerates all occurrences of expression e in text p using match_flag_type m.

Examples

The following example takes a C++ source file and builds up an index of class names, and the location of that class in the file.

#include <string>
#include <map>
#include <fstream>
#include <iostream>
#include <boost/regex.hpp>

using namespace std;

// purpose:
// takes the contents of a file in the form of a string
// and searches for all the C++ class definitions, storing
// their locations in a map of strings/int's

typedef std::map<std::string, std::string::difference_type, std::less<std::string> > map_type;

const char* re =
   // possibly leading whitespace:   
   "^[[:space:]]*"
   // possible template declaration:
   "(template[[:space:]]*<[^;:{]+>[[:space:]]*)?"
   // class or struct:
   "(class|struct)[[:space:]]*"
   // leading declspec macros etc:
   "("
      "\\<\\w+\\>"
      "("
         "[[:blank:]]*\\([^)]*\\)"
      ")?"
      "[[:space:]]*"
   ")*"
   // the class name
   "(\\<\\w*\\>)[[:space:]]*"
   // template specialisation parameters
   "(<[^;:{]+>)?[[:space:]]*"
   // terminate in { or :
   "(\\{|:[^;\\{()]*\\{)";


boost::regex expression(re);
map_type class_index;

bool regex_callback(const boost::match_results<std::string::const_iterator>& what)
{
   // what[0] contains the whole string
   // what[5] contains the class name.
   // what[6] contains the template specialisation if any.
   // add class name and position to map:
   class_index[what[5].str() + what[6].str()] = what.position(5);
   return true;
}

void load_file(std::string& s, std::istream& is)
{
   s.erase();
   s.reserve(is.rdbuf()->in_avail());
   char c;
   while(is.get(c))
   {
      if(s.capacity() == s.size())
         s.reserve(s.capacity() * 3);
      s.append(1, c);
   }
}

int main(int argc, const char** argv)
{
   std::string text;
   for(int i = 1; i < argc; ++i)
   {
      cout << "Processing file " << argv[i] << endl;
      std::ifstream fs(argv[i]);
      load_file(text, fs);
      // construct our iterators:
      boost::sregex_iterator m1(text.begin(), text.end(), expression);
      boost::sregex_iterator m2;
      std::for_each(m1, m2, &regex_callback);
      // copy results:
      cout << class_index.size() << " matches found" << endl;
      map_type::iterator c, d;
      c = class_index.begin();
      d = class_index.end();
      while(c != d)
      {
         cout << "class \"" << (*c).first << "\" found at index: " << (*c).second << endl;
         ++c;
      }
      class_index.erase(class_index.begin(), class_index.end());
   }
   return 0;
}