How can I access all matches of a repeated capture group, not just the last one?

My code is:

#include <boost/regex.hpp>
boost::cmatch matches;
boost::regex_match("alpha beta", matches, boost::regex("([a-z])+"));
cout << "found: 开发者_C百科" << matches.size() << endl;

And it shows found: 2 which means that only ONE occurrence is found… How to instruct it to find THREE occurrences? Thanks!

You should not call matches.size() before verifying that something was matched, i.e. your code should look rather like this:

#include <boost/regex.hpp>
boost::cmatch matches;
if (boost::regex_match("alpha beta", matches, boost::regex("([a-z])+")))
    cout << "found: " << matches.size() << endl;
else
    cout << "nothing found" << endl;

The output would be "nothing found" because regex_match tries to match the whole string. What you want is probably regex_search that is looking for substring. The code below could be a bit better for you:

#include <boost/regex.hpp>
boost::cmatch matches;
if (boost::regex_search("alpha beta", matches, boost::regex("([a-z])+")))
    cout << "found: " << matches.size() << endl;
else
    cout << "nothing found" << endl;

But will output only "2", i.e. matches[0] with "alpha" and matches[1] with "a" (the last letter of alpha - the last group matched)

To get the whole word in the group you have to change the pattern to ([a-z]+) and call the regex_search repeatedly as you did in your own answer.

Sorry to reply 2 years late, but if someone googles here as I did, then maybe it will be still useful for him...

This is what I've found so far:

text = "alpha beta";
string::const_iterator begin = text.begin();
string::const_iterator end = text.end();
boost::match_results<string::const_iterator> what;
while (regex_search(begin, end, what, boost::regex("([a-z]+)"))) {
    cout << string(what[1].first, what[2].second-1);
    begin = what[0].second;
}

And it works as expected. Maybe someone knows a better solution?

This works for me, maybe somebody will find it usefull..

std::string arg = "alpha beta";
boost::sregex_iterator it{arg.begin(), arg.end(), boost::regex("([a-z])+")};
boost::sregex_iterator end;
for (; it != end; ++it) {
  std::cout << *it << std::endl;
}

Prints:

alpha
beta