The use of O_BINARY where available was in the very first back-of-the-envelope suggestion from Tom Christiansen in March 2000. I admit to not really thinking through the consequences but clearly Tom imagined that most temp files would be binary rather than text. There is a bit of a backwards compatibility issue with changing the default to text, so any option would have to be provided in addition to current usage. I would be open to a TEXTMODE patch that has been tested on windows. I've never really had a Windows box for testing things on and no user has ever offered patches to get it working properly on windows.
Couple of asides:
- tmpnam is not safe. By the time you get round to using it the file could have been taken by someone else.
- You should be teaching people the OO interface rather than the subroutine interface. It has the advantage that the file is deleted at the correct time. This is a real problem on windows where you can't delete an open file (at least not without using Win32 calls that I can't test). Using new() and newdir() methods give much better control and more predictable file deletion instead of relying on END blocks.