On Saturday, January 17, 2015 13:47:37 via Digitalmars-d-learn wrote: > Is it currently possible to get the path to a safe temporary > file, i.e. one that is guaranteed to be freshly created and will > not override another existing file? > > There's `std.file.tempDir`, which doesn't create a unique file. > Then there's `std.stdio.tmpfile()`, which does, but it returns a > `File` object, and its `name` property is `null`. > > Did I miss something? IMO this is very import functionality. One > use case is passing these names as command line arguments to an > external program that doesn't support stdin/stdout.
The _only_ way to this write is to randomly generate a file name and then open the file with O_CREAT | O_EXCL (or more likely, O_RDWR | O_CREAT | O_EXCL), and then retry with a new name if the creation fails (good enough random name generation would likely require only two attempts at most). Simply randomly generating a file name is not enough, because it's still technically possible for the file to already exist (even if it's unlikely), and even checking for the file's existence prior to opening it isn't enough, because technically, the file could be created by another program in the small amount of time between when you checked for the file's existence and tried to create it. POSIX actually has mkstemp for doing this for you, but on some operating systems, it restricts the number of random files that it can generate to as little as 26 (at least, that's what I recall the number being). I don't think that any of the POSIX systems that we currently support have an implementation of mkstemp that's quite that bad, but all in all, I don't think that using mkstemp is a good idea. The problem is solved simply enough by randomly generating a file name (e.g. with rndGen()) and then using the correct flags with open. And I actually have code that does this that I was working on getting into Phobos, but the problem was getting access to the correct function on Windows (_wsopen_s, I believe). It wasn't available in druntime, and I didn't get around to fixing that (IIRC, because I started looking into the whole problem of how to deal with windows bindings in druntime in general and going down a rat hole that I didn't have time for). So, I never finished that pull request, and I really should get back to it. But I think that what we need is a function in std.stdio (e.g tempFile insteaf of tmpfile) which returns an open File with a randomly generated name and gives you access to its name rather than using C's tmpfile, which does not give you access to the name and deletes the file on you when it's closed. IMHO, tmpfile is pretty useless - especially when it comes to unit tests. - Jonathan M Davis
