Thanks Guys, Yes I was not planning to use -[NSURL isEqual:]. Interestingly, Graham¹s suggestion was to use NSSet, I was thinking what if I want to keep this persistent? I would be writing this set to a file? I have used NSArray writeToFile before but I don¹t see that method for NSSet. Do I have to convert it to NSArray and store? Am I missing something?
I figured if I put resource identifier object into the NSMutableSet then will I be able to write this into a file? I know it is possible if I store it as NSString but might not allow id? Regards, Varun On 15/04/2014 12:01 pm, "Ken Thomases" <k...@codeweavers.com> wrote: >On Apr 14, 2014, at 7:02 PM, Varun Chandramohan wrote: > >> I have a question about efficiency when trying to compare NSURL. The >>requirement is quite simple. I try and iterate through a directory to >>all subdirectories and files. While doing this walk-through, I need to >>check against an array of NSURLs which are restricted files and folders. >> This means if I find a match of file I am trying to access in the array >>then I don't do any operations on that file and continue. > >You don't say how you're comparing URLs. Just in case, you should not >use -[NSURL isEqual:] or any method which relies on string comparison. >That can be confused by case differences, the presence of hard or >symbolic links, and extraneous path elements (e.g. "foo/./bar" vs. >"foo/bar"). > >You should obtain the resource identifier object of each URL using >-getResourceValue:forKey:error: with NSURLFileResourceIdentifierKey, then >compare those two objects using -isEqual:. > >If you take Graham's suggestion of using an NSSet or similar hash-based >collection to test, then put the resource identifiers of the restricted >files into the set and check a candidate URL's resource identifier >against that set. > >For what it's worth, comparing resource identifiers may be faster than >the string comparison otherwise inherent in -[NSURL isEqual:]. The >identifier is likely to be a number or pair of numbers internally and so >is quick to compare. That said, the improvement may be swamped by the >cost of obtaining the resource identifier object. > > >> Secondly, I plan to store array of NSURL for restricted files and >>folders. What is the best way to get partial compare? >> >> Eg: Entry in array : /XYZ/abc >> This means I should not iterate into the abc folder. So any files >>/XYZ/abc/1.c or /XYZ/abc/def/2.c should all be skipped. Whats the best >>way to do partial NSURL compare? Or is it better I store it as NSString >>instead of NSURL? > >Don't try to do substring compares. Since you're iterating a directory >hierarchy, you should simply not iterate a subdirectory if it matches. >When using NSDirectoryEnumerator, that's easy to do: just call >-skipDescendants. > >If you feel you must compare two URLs to see if one is contained in the >other, you'll probably have to successively obtain the parent directory >URL from the candidate URL using -getResourceValue:forKey:error: with >NSURLParentDirectoryURLKey until you've reached the top of the hierarchy >or you have matched one of your restricted file URLs. > >You _might_ want to optimize that by obtaining the >NSURLVolumeIdentifierKey of each URL and then determining that one >doesn't contain the other if the two URLs are for different volumes. >Whether that's appropriate or not depends on whether you care about >path-based containment or file-system-based containment. "/foo/bar/baz" >may be on a different volume than "/foo" and you have to decide whether >that means that it's not contained by "/foo". > >Regards, >Ken > _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
