#include <iostream>
#include <regex>
 
int main()
{
    std::regex pattern { "ab*" };
    std::cout << "'ab*' match with '': " << std::boolalpha << 
        std::regex_match("", pattern) << std::endl;
 
    std::cout << "'ab*' match with 'ab': " << std::boolalpha << 
        std::regex_match("ab", pattern) << std::endl;
 
    std::cout << "'ab*' match with 'abab': " << std::boolalpha << 
        std::regex_match("abab", pattern) << std::endl << std::endl;
 
    pattern = "(ab)*";
    std::cout << "'(ab)*' match with '': " << std::boolalpha << 
        std::regex_match("", pattern) << std::endl;
 
    std::cout << "'(ab)*' match with 'ab': " << std::boolalpha << 
        std::regex_match("ab", pattern) << std::endl;
 
    std::cout << "'(ab)*' match with 'abab': " << std::boolalpha << 
        std::regex_match("abab", pattern) << std::endl;
}