My test program was as follows: [Code] // fly.cpp : main project file. #include "stdafx.h" #include <string> #include <iostream> #include <vector> #include <fstream> #include <iterator> #include <algorithm> #include <boost/progress.hpp> #include <boost/flyweight.hpp> using namespace std; vector<boost::flyweight<string> > vec; //vector<string> vec; struct Insert { void operator()(string s) { vec.push_back(boost::flyweight<string>(s)); //vec.push_back(s); } }; void Test() { fstream f("d:\\bible12.txt", ios_base::in); // A large text file! { boost::progress_timer t; for_each(istream_iterator<string>(f), istream_iterator<string>(), Insert()); } } int main(int argc, char* argv[]) { Test(); cout << vec.size() << endl; getchar(); copy(vec.begin(), vec.begin() + 200, ostream_iterator<string, char>(cout, " ")); getchar(); return 0; } [/Code] Using the boost_1_35_0 svn library download and Visual C++ 2008 Express edition. Originally compiled as a CLR program. Recompiling using native Win32 still gives a crash during program termination - in atomic_count_win32.hpp in operator-- (BOOST_INTERLOCKED_DECREMENT) Unhandled exception at 0x010752b9 in fly2.exe: 0xC0000005: Access violation writing location 0x00779040. There is still the anomaly of release version being slower than debug. Compiled as release - the exception occurs in xmemory in _Destroy_range. I'll experiment using set_factory in Borland - although I have largely abandoned it's use, just can't compile enough of Boost to be useful now... Martin