#include <iostream>
#include <regex>
 
int main()
{
    std::regex const pattern { "[123[:alpha:]]" };
    std::cout << "'[123[:alpha:]]' match with 'a': " << std::boolalpha << 
        std::regex_match("a", pattern) << std::endl;
        
    std::cout << "'[123[:alpha:]]' match with '1': " << std::boolalpha << 
        std::regex_match("1", pattern) << std::endl;
        
    std::cout << "'[123[:alpha:]]' match with '4': " << std::boolalpha << 
        std::regex_match("4", pattern) << std::endl;
        
    std::cout << "'[123[:alpha:]]' match with '&': " << std::boolalpha << 
        std::regex_match("&", pattern) << std::endl;
}