How to format a datetime to string using boost?

Question

I want to format a date/time to a string using boost.

Starting with the current date/time:

ptime now = second_clock::universal_time();

Answer 1

// create your date
boost::gregorian::date d(2009, 1, 7); 

// create your formatting
boost::gregorian::date_facet *df = new boost::gregorian::date_facet("%Y%m%d_%H%M%S"); 

// set your formatting
ostringstream is;
is.imbue(std::locale(is.getloc(), df));
is << d << endl;

// get string
cout << "output :" << is.str() << endl;

Answer 2

For whatever it is worth, here is the function that I wrote to do this:

#include "boost/date_time/posix_time/posix_time.hpp"
#include <iostream>
#include <sstream>

std::wstring FormatTime(boost::posix_time::ptime now)
{
  using namespace boost::posix_time;
  static std::locale loc(std::wcout.getloc(),
                         new wtime_facet(L"%Y%m%d_%H%M%S"));

  std::basic_stringstream<wchar_t> wss;
  wss.imbue(loc);
  wss << now;
  return wss.str();
}

int main() {
  using namespace boost::posix_time;
  ptime now = second_clock::universal_time();

  std::wstring ws(FormatTime(now));
  std::wcout << ws << std::endl;
  sleep(2);
  now = second_clock::universal_time();
  ws = FormatTime(now);
  std::wcout << ws << std::endl;

}

The output of this program was:

20111130_142732
20111130_142734

I found these links useful:

• How to format date time object with format dd/mm/yyyy?
• http://www.boost.org/doc/libs/1_35_0/doc/html/date_time/date_time_io.html#date_time.time_facet
• http://www.cplusplus.com/reference/iostream/stringstream/str/