Question

I have a std::string such as 20040531, I want to format this as 2004.05.31.

Apart from the straight forward way of doing an std::insert at respective locations, is there a better way to do this using Boost?

PS. I cannot use other Boost calls to get date/time as this string is returned via a custom API. So this question is reduced to basic string formatting which may not sound exciting, but I am trying to learn Boost.

Answer 1

You could use boost::format…

#include <string> 
#include "boost/format.hpp"
#include <iostream>

int main()
{
    std::string a("20040531");
    std::cout << boost::format("%1%.%2%.%3%") 
                    % a.substr(0,4) % a.substr(4,2) % a.substr(6,2);
}

You specifically asked about doing this using Boost, but if you wanted to do this in C++ without introducing a dependency on Boost then you could just use a stream to achieve the same thing:

#include <sstream>
#include <string>
#include <iostream>

int main()
{
    std::stringstream s;
    std::string a("20040531");
    s << a.substr(0,4) << '.' << a.substr(4,2) << '.' << a.substr(6,2);
    std::cout << s.str();
}