Commander Pirx wrote: ------------------------------------------ Would be interesting whats your format string looks like. Not all format flags work with all date_time classes. %z (Time zone) for instance works only with local_date_time. ------------------------------------------ It seems that no matter what formatting I try to use, it doesn't work. Example: TimeConverter sampleFile.txt %d:%m:%Y_%H:%M:%S %m:%d:%Y_%H:%M:%S sampleFile.txt: 05:01:2007_23:08:02 06:01:2007_23:09:04 expected output: (month and day positions switched) 2007-Jan-05 23:08:02 01:05:2007_23:08:02 2007-Jan-06 23:09:04 01:06:2007_23:09:04 output: 2007-Jan-05 23:08:02 2007-Jan-05 23:08:02 2007-Jan-06 23:09:04 2007-Jan-06 23:09:04 Code is below #include <fstream> #include <functional> #include <iostream> #include <sstream> #include "boost/date_time/gregorian/gregorian.hpp" #include "boost/date_time/posix_time/posix_time.hpp" #include "boost/date_time/local_time/local_time.hpp" using namespace std; int main(int argc, char** argv) { stringstream ss; ifstream in( argv[1] ); string inputFormat = argv[2]; string outputFormat = argv[3]; boost::local_time::local_time_facet* output_facet = new boost::local_time::local_time_facet(); boost::local_time::local_time_input_facet* input_facet = new boost::local_time::local_time_input_facet(); ss.imbue(locale(locale::classic(), output_facet)); ss.imbue(locale(ss.getloc(), input_facet)); output_facet->format( outputFormat.c_str() ); input_facet->format( inputFormat.c_str() ); while ( !in.eof() ) { string s; getline( in, s ); ss<>p; string s1 = boost::posix_time::to_simple_string(p); cout<