On 10 Jun 2011, at 14:28, Jens Alfke wrote:
>
> On Jun 10, 2011, at 12:51 PM, Jerry Krinock wrote:
>
>> do {
>> newPath = [[[newPath stringByDeletingPathExtension]
>> stringByAppendingString:suffix]
>> stringByAppendingPathExtension:[self pathExtension]] ;
>> } while ([[NSFileManager defaultManager] fileExistsAtPath:newPath]) ;
>
> This will work most of the time, but it has a race condition: just because
> there was no file at that path when this method returns, is no guarantee that
> there’s still no such file when the caller attempts to create a file at the
> returned path. (This seems unlikely, but it can happen when two apps using
> the same code are trying to create a file at the same time. It’s also
> sometimes been exploited by malware to substitute a malicious file for the
> real one a system task thought it was creating.)
>
> This race condition is pretty well known, and it’s generally considered wrong
> to test for existence prior to operating on a file. Instead, do the operation
> without checking and handle the error. (Sometimes called “ask for
> forgiveness, not permission”.)
>
> So the correct code would look like:
>
> do
> compute a new filename to use on this iteration
> try to copy to that filename
> while the copy failed with a ‘duplicate filename’ error
I've built a nice helper for this:
http://www.mikeabdullah.net/incrementing-paths.html_______________________________________________
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