Does DirectoryInfo.EnumerateDirectories sort items?

Question

I have an application that has to enumerate a few folders and process the files inside them.

It has to support resuming, meaning it has to start from the folder it was processing the last time.

I was thinking of using the DirectoryInfo.EnumerateDirectories method. I'd save the name of the last processed dir in a file, skip the enumeration until I meet that dir name and continue processing from there.

However, the documentation does not say anything about the order in which files are enumerated.

Is it safe to assume that using this method the program will always process the remaining directories? Or is it possible that the next time the program runs the directories will be enumerated in another order, thus making it possible to leave some unprocessed and process others two times?

If this method is not safe, what would be a good alternative?

Answer 1

Internally EnumerateDirectories() uses Win32 API FindNextFile() (source code). From MSDN:

"The order in which the search returns the files, such as alphabetical order, is not guaranteed, and is dependent on the file system."

Answer 2

DirectoryInfo.EnumerateDirectories() return IEnumerable<DirectoryInfo> in your msdn doc. I don't think it is already sorted and even if it is sorted, have question on sorted by which field or property of DirectoryInfo. You can do sorting by yourself on query.

// Create a DirectoryInfo of the Program Files directory.
DirectoryInfo dirPrograms = new DirectoryInfo(@"c:\program files");

DateTime StartOf2009 = new DateTime(2009, 01, 01);
// LINQ query for all directories created before 2009.
var dirs = (from dir in dirPrograms.EnumerateDirectories()
                where dir.CreationTimeUtc < StartOf2009
                order by dir.Name).ToList();