Microseconds get cut off in ISO string representation if all zero (posix_time::to_iso_string)

[Marcel Glacki <boost-trac@…>]

#include <iostream>
#include <string>
#include <boost/date_time/posix_time/posix_time.hpp>


int main()
{
    boost::posix_time::ptime timestamp = boost::posix_time::microsec_clock::local_time();
    std::string sTime( boost::posix_time::to_iso_string( timestamp ));
    std::cout << "Timestamp: " << sTime << std::endl;
    return 0;
}

This outputs for example: Timestamp: 20151121T141522.999982

Now, if microseconds are all zero the output I'd expected was
Timestamp: 20151121T141523.000000
but actually is
Timestamp: 20151121T141523

Now, when trying to cut off the microseconds fraction (for whatever reason) by doing

std::string sFraction = sTime.substr( 16, 21 );

you may end up with the following error:

Something unexpected happened: 'basic_string::substr: __pos (which is 16) > this->size() (which is 15)'

I saw this behavior in Boost 1.55.0, but when I checked the current sources online, I couldn't see any difference, so I think this would occur in the current version, too.