Boost C++ Libraries

The algorithm regex_split has been deprecated in favor of the iterator regex_token_iterator which has a more flexible and powerful interface, as well as following the more usual standard library "pull" rather than "push" semantics.

Code which uses regex_split will continue to compile, the following documentation is taken from a previous Boost.Regex version:

#include <boost/regex.hpp>

Algorithm regex_split performs a similar operation to the perl split operation, and comes in three overloaded forms:

template <class OutputIterator, class charT, class Traits1, class Alloc1, class Traits2>
std::size_t regex_split(OutputIterator out,
                        std::basic_string<charT, Traits1, Alloc1>& s,
                        const basic_regex<charT, Traits2>& e,
                        boost::match_flag_type flags,
                        std::size_t max_split);

template <class OutputIterator, class charT, class Traits1, class Alloc1, class Traits2>
std::size_t regex_split(OutputIterator out,
                        std::basic_string<charT, Traits1, Alloc1>& s,
                        const basic_regex<charT, Traits2>& e,
                        boost::match_flag_type flags = match_default);

template <class OutputIterator, class charT, class Traits1, class Alloc1>
std::size_t regex_split(OutputIterator out,
                        std::basic_string<charT, Traits1, Alloc1>& s);

Effects: Each version of the algorithm takes an output-iterator for output, and a string for input. If the expression contains no marked sub-expressions, then the algorithm writes one string onto the output-iterator for each section of input that does not match the expression. If the expression does contain marked sub-expressions, then each time a match is found, one string for each marked sub-expression will be written to the output-iterator. No more than max_split strings will be written to the output-iterator. Before returning, all the input processed will be deleted from the string s (if max_split is not reached then all of s will be deleted). Returns the number of strings written to the output-iterator. If the parameter max_split is not specified then it defaults to UINT_MAX. If no expression is specified, then it defaults to "\s+", and splitting occurs on whitespace.

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).

Example: the following function will split the input string into a series of tokens, and remove each token from the string s:

unsigned tokenise(std::list<std::string>& l, std::string& s)
{
   return boost::regex_split(std::back_inserter(l), s);
}

Example: the following short program will extract all of the URL's from a html file, and print them out to cout:

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

boost::regex e("<\\s*A\\s+[^>]*href\\s*=\\s*\"([^\"]*)\"",
               boost::regbase::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()-&gtin_avail());
   char c;
   while(is.get(c))
   {
      // use logarithmic growth strategy, 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;
   std::list<std::string> l;

   for(int 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::regex_split(std::back_inserter(l), s, e);
      while(l.size())
      {
         s = *(l.begin());
         l.pop_front();
         std::cout << s << std::endl;
      }
   }
   return 0;
}