Time changes, localtime and file names

[blssu]

It's nice for users to name files using local time, but you have to watch out for time changes! Many locales have some sort of day light savings time which seasonally adjusts localtime() (but not time() -- that keeps marching forward).

For example, in the U.S. this fall, the time period from midnight to 2 am will occur twice in the same day. If you don't check your file names for collisions, you may destroy existing files.