C++ 정규표현식좀 봐주세요.

#include <iostream>
#include <string>
#include <regex>
 
int main ()
{
  std::string s ("test subject");
  std::smatch m;
  std::regex e ("(sub)(.*)");
 
  std::regex_search ( s, m, e );
 
  cout<<m.size();
 
  return 0;
}