Hi, With Visual C++, I can't seem to determine why if I simply include boost/threads/once.hpp, I need to enable language extensions for that translation unit. I'm going to dig into this further today but I would appreciate if someone has figured out a solution short of allowing language extensions. I can understand requiring it for building boost threads (as windows.h seems to have some extended syntax) but I'm not sure of the logic behind requiring client code to use it as well. Thanks for listening :) Sohail