generate_boost_date.cpp

#include <string>
#include <iostream>

#include <boost/regex.hpp>
#include <boost/date_time/gregorian/gregorian.hpp>

int main(int argc, char** argv) {
    boost::regex date(R"((\d{2})\.(\d{2})\.(\d{4}))");

    boost::smatch match;
    boost::gregorian::date d;
    std::ostringstream ss;

    std::string filename(" of 18.05.2017.txt");

    if (boost::regex_search(filename, match, date)) {
    	std::cout << match[0] << std::endl;
    	std::cout << match[1] << std::endl;
    	std::cout << match[2] << std::endl;
    	std::cout << match[3] << std::endl;

        d = boost::gregorian::date(std::stoi(match[3]), std::stoi(match[2]), std::stoi(match[1]));
        ss << d.day() << ' ' << d.month().as_number() << ' ' << d.year() << '\n';

        std::cout << ss.str();

    }

}