c++ - issue with creating boost date from string -

i have piece of code tries create boost::gregorian::date object string format end getting boost:gregorian::not_a_date_time though string seems fine. code looks this:

boost::gregorian::date getdatefromstring(std::string date_str, std::string format) const     {         const std::locale loc = std::locale(std::locale::classic(), new boost::gregorian::date_facet(format.c_str()));          std::istringstream is(date_str) ;          is.imbue(loc);         boost::gregorian::date d;          >> d;          return d;      } 

to test call

boost::gregorian::date d = getdatefromstring("20161101","%y%m%d") ;  

i not_a_date_time returned; instead if following:

boost::gregorian::date d2 = boost::gregorian::date_from_iso_string( "20161101"); 

i receive proper date object back. need generic function can take variety of date formats. doing wrong here?

you using date_facet instead of date_input_facet:

#include <boost/date_time.hpp> #include <boost/date_time/gregorian/gregorian_io.hpp>  boost::gregorian::date getdatefromstring(std::string date_str, std::string format) {     const std::locale loc = std::locale(std::locale(), new boost::gregorian::date_input_facet(format.c_str()));      std::istringstream is(date_str);      is.imbue(loc);     boost::gregorian::date d;      is.exceptions(~std::ios::iostate::_s_goodbit);     >> d;      return d;  }  int main() {     boost::gregorian::date d = getdatefromstring("20161101","%y%m%d");      std::cout << d; } 

note use of exceptions() see parser thinks wrong if fails parse. don't want enable unless handle exception.

live on coliru

prints

2016-nov-01