std::regex reg1("[^13579,]");
std::string str1="1,2,3,4,5,6,7,8,9,10,11,12";
std::sregex_iterator it1(str1.begin(),str1.end(),reg1);
std::sregex_iterator end1;
std::cout << "Character Stream: " << std::endl;
while (it1 != end1) std::cout << " " << *it1++;
std::cout << "\n\n";

std::regex reg2(",");  
std::string str2="1,2,3,4,5,6,7,8,9,10,11,12";
std::sregex_token_iterator it2(str2.begin(),str2.end(),reg2,-1);
std::sregex_token_iterator end2;
std::cout << "Token Stream: " << std::endl;
while (it2 != end2) std::cout << "  "  << *it2++;
std::cout << "\n";