I'll just throw my 2 shillings in here. ochkam is correct. Each C/C++ (and other) source code file is compiled into a .obj which is then used by the linker to assemble them into an executable (or library, dynamic link library (dll), plugin, etc). M$ has done everybody a disservice by using the extension as a determination of file type instead of the contents (MIME type or whatever). There are basically two types of file: text and binary. The contents should determine what the exact use and association of the file are and not the extension. That should only be a "clue" as to what the contents might be, but not the definition. This is why Windows is such an easy target for viruses, malicious scripts, and whatnot. BYS