chaps, I am using gcc to compile a old peaice of code. that has so many header file with #ifdef WIN_OS slls #elseif UNIX_OS abs #else #error missing os Now i am getting into this last statement time & again. I am not sure what to define of that header file try compile UNIX_OS. IS thier any standard macro that I need to define in my makefile so that OS can be specifed. Any help is much appriatied -- View this message in context: http://old.nabble.com/compiler-macro-that-define-operating-system-tp29723027p29723027.html Sent from the gcc - Help mailing list archive at Nabble.com.