std::regex

main.cpp

#include <iostream>
#include <regex>
#include <string>

int main() {
	std::string str{ "The ip address 127.0.0.1:8080 had been blocked." };
	std::string pattern{ "(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})" };
	std::cout << "input str: " << str << std::endl;
	std::cout << "pattern str: " << pattern << std::endl;

	std::regex re(pattern, std::regex::icase);
	if (std::smatch ret; std::regex_search(str, ret, re)) {
		std::cout << "found the str: " << ret.str() << std::endl;
		std::cout << "has subgroup: " << ret.size() - 1 << std::endl;
        for (auto&& [i, subgroup] = std::make_pair(1, ret.begin()+1); subgroup != ret.cend(); ++subgroup, ++i) {
            const std::ptrdiff_t begin = ret.position(i);
            std::cout << "\t - [" << i << "] at (" << begin << ", " << begin + subgroup->length() << ") : " << subgroup->str() << std::endl;
		}
	}

    
	return 0;
}